Terms Starting with "L"

738 terms

L data

L data life data: information about an individual gathered from his or her life record or life history. See also O data; Q data; T data.

L-alpha-acetyl-methadol

L-alpha-acetyl-methadol n. see LAAM.

L-dopa

L-dopa n. see levodopa.

L-methylfolate

L-methylfolate n. the active form of the B vitamin folate. It is available as a prescription medical food to treat people with folate deficiencies, depression (as an adjunct to antidepressants), or schizophrenia (as an adjunct to antipsychotics). U.S. trade name: Deplin.

la belle indifférence

la belle indifférence inappropriate lack of concern about the implications or seriousness of one’s physical symptoms, often seen in conversion disorder.

LAAM

LAAM L-alpha-acetyl-methadol: a long-acting opioid agonist that is a chemical analog of methadone. A strong agonist at the mu opioid receptor, it can be used in oral form in the management of opioid dependence because of its ability to suppress physical withdrawal symptoms and block the reinforcing effects of opioids. It has a longer half-life (about 72 hours) than methadone and therefore needs to be taken less frequently, a major advantage over methadone (which is taken daily). However, due to its possible adverse effects on heart rate and its interactions with other drugs, LAAM is no longer manufactured in the United States, Europe, and Canada.

labeled lines

labeled lines nerve inputs to the brain that one conceptualized as each reporting only one particular type of information.

labeled-line theory of taste coding

labeled-line theory of taste coding a theory postulating that each gustatory neuron type comprises a private circuit through which the presence of its associated primary taste quality is signaled. The taste is perceived exclusively as a product of activity in that labeled line; activity in neurons outside the labeled line contributes only noise. Compare pattern theory of taste coding.

labeling

labeling n. 1. in psychological assessment, classifying a patient according to a certain diagnostic category. Patient labeling may be incomplete or misleading, because not all cases conform to the sharply defined characteristics of standard diagnostic categories. 2. medication information provided on a drug container or package insert (also called direction circular or package circular) that specifies indications, side effects, dosages, mechanisms of action, and other information necessary for a physician to prescribe the medication correctly. Drug labeling in the United States is regulated by the U.S. Food and Drug Administration. Also called prescribing information (PI); professional labeling.

labeling theory

labeling theory the sociological hypothesis that describing an individual in terms of particular behavioral characteristics may have a significant effect on his or her behavior, as a form of self-fulfilling prophecy. For example, describing an individual as deviant and then treating him or her as such may result in mental disorder or delinquency. Also called societal-reaction theory. See also primary deviance.

labia

labia pl. n. (sing. labium) four lip-shaped folds of tissue forming part of the female external genitalia (see vulva). The labia—comprising a larger, outer pair, the labia majora (sing. labium majus), and a thinner, inner pair, the labia minora (sing. labium minus)—enclose the clitoris and the openings of the urethra and vagina.

labial

labial 1. adj. of or relating to the lips. 2. adj. denoting a speech sound made with the lips, for example, [b], [p], [m], [w], [f], or [v]. If the sound is made with both lips, it is described as bilabial; if the sound is made with the lower lip and the upper teeth, it is termed labiodental. 3. n. a labial speech sound.

labile

labile adj. 1. liable to change, as in labile affect. 2. describing the early stage of memory formation that can be easily disrupted by factors influencing brain activity. —lability n.

labile affect

labile affect highly variable, suddenly shifting emotional expression.

labio-

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labiodental

labiodental 1. adj. denoting a speech sound made with the lower lip touching or near the upper teeth, such as [f] or [v]. 2. n. a labiodental speech sound. Also called labial dental. See labial.

labor

labor n. the first stage of childbirth, from the dilation of the cervix until the infant’s head begins to enter the birth canal. See delivery.

Labor Management Relations Act

Labor Management Relations Act a series of amendments to the National Labor Relations Act that were passed in 1947 to adjust the power balance between unions and employers in the United States, the previous system being regarded as too restrictive of management. The act identified and prohibited certain unfair labor practices of both unions and employers, created the Federal Mediation and Conciliation Service to aid in resolution of disputes, and provided a mechanism for dealing with strikes that create a national emergency. Sponsored by U.S. lawyer and politician Robert Alphonso Taft (1889–1953) and U.S. politician Fred Allan Hartley Jr. (1902–1969), it is also known as the Taft–Hartley Act.

labor relations

labor relations 1. relations between employers and employees or between employers and unions, especially within the context of collective bargaining. 2. a multidisciplinary field of study devoted to understanding and managing employee–employer or union–employer relations. Also called industrial relations.

labor turnover

labor turnover see turnover.

labor union

labor union see union.

laboratory research

laboratory research scientific study conducted in a laboratory or other such workplace, where the investigator has some degree of direct control over the environment and can manipulate the independent variables. Although laboratory research generally has greater internal validity than field research does, it tends to be less generalizable to the real world (i.e., has less external validity). See experimental research.

laboratory-method model

laboratory-method model an approach to education in which the role of social interaction is emphasized. The development of personal awareness and interpersonal skills is a major area of concern.

labyrinth

labyrinth n. in anatomy, the complex system of cavities, ducts, and canals within the temporal bone of the skull that makes up the inner ear. The bony (or osseous) labyrinth is a system of bony cavities that houses the membranous labyrinth, a membrane-lined system of ducts containing the receptors for hearing and balance.

labyrinthine sense

labyrinthine sense see sense of equilibrium.

labyrinthitis

labyrinthitis n. infection or inflammation of the inner ear, which may result in dizziness, loss of balance, or partial or temporary loss of hearing.

laceration

laceration n. a jagged tear or cut: a wound with rough, irregular edges.

lack of fit

lack of fit the degree to which the values predicted by a model—typically, one developed in regression analysis, structural equation modeling, or confirmatory factor analysis—diverge from the corresponding empirical values. A large, significant value from a goodness-of-fit test indicates a poorly fitting model.

lacrimal gland (lachrymal gland)

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lacrimal reflex

lacrimal reflex the secretion of tears in response to a variety of stimuli, including those that irritate receptors in the nose.

lacrimation

lacrimation n. crying, especially excessive crying.

lactate dehydrogenase (LDH)

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lactation

lactation n. 1. the formation and release of milk by the mammary glands. It is a form of nursing that occurs only in female mammals and is divided into lactogenesis—the initiation of milk production—and galactopoiesis—the subsequent maintenance of milk production and secretion. The former is itself divided into Lactogenesis Stage I, which in humans generally lasts from mid-pregnancy through 2 days following childbirth, and Lactogenesis Stage II, which occurs within 3 to 8 days after birth. In Lactogenesis Stage I, the various mammary cells enlarge, reorganize into large clumps resembling grapes, and start producing a nutrient- and antibody-rich fluid known as colostrum that is eventually released during the initial days of nursing. In Lactogenesis Stage II, the enlarged mammary cells fill with copious amounts of mature milk once the maternal placenta is expelled and no longer introducing progesterone, which inhibits milk formation, into the bloodstream. In the subsequent galactopoiesis phase, beginning around 9 days after birth, the mammary cells continuously produce mature milk in response to its repeated removal by the suckling infant or by a breast pump. Lactation is regulated primarily by the hormones prolactin, which facilitates and sustains milk production, and oxytocin, which stimulates the milk letdown reflex to faciliate milk excretion. Lactation is an energy-intensive process that places significant metabolic demands on the female system, requiring not only increased caloric intake but also considerable amounts of calcium and other minerals. See also galactorrhea. 2. the period during which this process occurs.

lacto-

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lactogenesis

lactogenesis n. see lactation.

lactogenic hormone

lactogenic hormone see prolactin.

lactotroph

lactotroph n. see prolactin.

lactotropic hormone

lactotropic hormone see prolactin.

lactotropin

lactotropin n. see prolactin.

lacuna

lacuna n. (pl. lacunae) a gap or break, such as a gap in memory. —lacunar adj.

lacunar amnesia

lacunar amnesia see localized amnesia.

lacunar stroke

lacunar stroke a stroke caused by small infarctions resulting from obstruction of small arterioles branching directly off large vessels in the brain. Lacunar strokes account for about 20% of all strokes.

LAD

LAD abbreviation for language acquisition device.

Ladd-Franklin theory

Ladd-Franklin theory a formerly influential but now superseded theory of color vision. It is based on the notion that light of certain wavelengths causes substances to be released from a highly developed photosensitive molecule in the retina and that these substances stimulate the retina, causing the perception of red, green, or blue. [introduced in 1929 by Christine Ladd-Franklin]

laddering

laddering n. a knowledge elicitation technique used in interviews to impose a systematic framework upon questioning so as to reveal complex themes across answers. In laddering, a respondent replies to a series of “why?” probes, thus requiring him or her to expose and explain choices or preferences and justify behavior in terms of goals, values, and personal constructs. Laddering is concerned with establishing links between concepts elicited from the participant (e.g., attitudes and beliefs associated with a particular consumer product) and provides greater scope for probing salient issues while optimizing the often limited time available with respondents.

lag

lag n. 1. a delay between a stimulus and a response. 2. a delay between the time a receptor is stimulated and the conscious awareness of the sensation.

lag effect

lag effect a cognitive phenomenon in which long-term retention of to-be-learned information improves with increased separation (lag) between repeated presentations of the information within a single period of study. Such lag is obtained by interspersing the material of interest with additional material or by increasing the number of overall elements between item repetitions. For example, a student preparing for a Spanish vocabulary exam would remember more from a study session by reviewing one long list of words multiple times instead of dividing it into three smaller lists because there would be a longer lag between the repeated presentations of each word in the former method. Although some use the terms synonymously, the spacing effect is an instance of the lag effect, referring to the improvement in memory that occurs when repetitions of material are distributed over multiple study sessions rather than when the material is studied in a single session (massed practice). One explanation of the lag effect is the differential-organization theory, which proposes that people organize presented material into overlapping groups (e.g., of interassociated words); that as lag increases, the groups overlap less and less; and that the probability of recalling a given word thus increases as a function of the number of different groups of words with which it has been associated. See also primacy effect; recency effect. [identified in 1967 by Arthur W. Melton]

lagophthalmos (lagophthalmus)

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laissez-faire leader

laissez-faire leader the type of leader who provides little guidance for group activities, interacts only minimally with the group members, and provides input only when directly asked. Research suggests that groups with laissez-faire leaders are less effective than are groups with democratic leaders or with authoritarian leaders. [defined by Kurt Lewin and his colleagues in experimental studies of leadership styles]

lalling

lalling n. an infantile form of speech characterized by the omission or substitution of sounds, particularly the substitution of the [l] sound for other sounds that are more difficult for the speaker to produce, for example, saying “lellow” for yellow. Lalling is considered a speech disorder when it persists beyond the age at which accurate articulation should have been acquired. See also phonological disorder.

lalopathy

lalopathy n. any form of speech disorder.

Lamarckism

Lamarckism n. the theory that changes acquired by an organism during its lifetime—for example, through use, disuse, or injury of particular parts—can be inherited by its offspring. Extensive research over centuries failed to find proof of such inheritance of acquired characteristics; however, evidence now suggests that epigenetic modifications (i.e., natural or environmentally induced changes to DNA expression that occur during an organism’s lifetime) can result in acquired characteristics that may be inherited by offspring. Also called use-and-disuse theory. [Jean-Baptiste Lamarck (1744–1829), French natural historian] —Lamarckian adj.

Lamaze method

Lamaze method a variation of the method of natural childbirth in which the mother learns about childbirth anatomy and physiology and practices pain management through relaxation, massage, and breathing exercises. The mother is aware and active during labor, guided by her partner, who shares in the birth experience (e.g., as a supportive coach). The method neither encourages nor discourages the use of medication during labor and delivery. See also Leboyer technique. [Ferdinand Lamaze (1890–1957), French obstetrician]

lambda

lambda 1. (symbol: λ) see eigenvalue. 2. (symbol: Λ) see Wilks’s lambda.

lambda model (λ model)

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Lambert’s law

Lambert’s law the principle that the illuminance of a surface lit by light falling on it perpendicularly from a point source is inversely proportional to the square of the distance between the surface and the source. [Johann Heinrich Lambert (1728–1777), French-born Prussian mathematician]

lamellipodium

lamellipodium n. (pl. lamellipodia) a sheetlike extension of a cell, for example, of the growth cone of a neuron.

laminar organization

laminar organization the horizontal layering of cells found in some brain regions. See cortical layers.

lamotrigine

lamotrigine n. an anticonvulsant drug used as an adjunct in the treatment of adults with partial seizures and some generalized seizures and for maintenance treatment of bipolar disorder. Although ineffective in treating acute manic episodes, it has gained acceptance as a single-drug treatment for acute bipolar depression and rapid-cycling bipolar II disorder. Serious skin reactions, including Stevens–Johnson syndrome, have been reported at the start of therapy, particularly in children. U.S. trade name: Lamictal.

LAMP

LAMP abbreviation for Learning Abilities Measurement Program.

Land effect

Land effect a demonstration used to develop the retinex theory of color vision. To produce the effect, a multicolored scene is photographed with black and white film, once through a red filter and once through a blue–green filter. When the resulting images are projected simultaneously onto a screen through the opposite filter used to photograph the image, the original multicolored scene is perceived. [Edwin Herbert Land (1909–1991), U.S. inventor]

Land theory of color vision

Land theory of color vision see retinex theory. [Edwin Herbert Land (1909–1991), U.S. inventor]

Landau reflex

Landau reflex a normal reaction observed in infants between the ages of 3 and 12 months: When the child is supported horizontally in the prone position, the head rises and the back arches. Absence of the reflex is a sign of a neurological disorder, such as cerebral palsy or motor neuron disease.

Landau–Kleffner syndrome

Landau–Kleffner syndrome a rare childhood neurological disorder of unknown cause that is characterized by the sudden or gradual development of aphasia (inability to understand or express language) and an abnormal electroencephalogram (see electroencephalography). The syndrome usually occurs in children between the ages of 5 and 7 years who develop normally but then lose their language skills for no apparent reason. Many children with the disorder experience seizures, which generally disappear by adulthood. [first described in 1957 by William M. Landau and Frank R. Kleffner]

landmark

landmark n. an external reference point that is a major component of a cognitive map. The design and placement of landmarks can significantly affect way-finding behavior. See environmental cognition; legibility.

Landmark Forum

Landmark Forum see Erhard Seminar Training.

Landolt circles

Landolt circles a set of circles with gaps of varying size, used to test visual acuity. Also called Landolt Cs. [Edmund Landolt (1846–1926), French ophthalmologist]

landscaped office

landscaped office a modification of the open-office design in which emphasis is given to the interaction of people, such that the arrangement of work spaces is based on patterns of communication and facilitation of work flow. Landscaped offices typically place supervisors near workers and group people who communicate regularly with one another to perform their job duties in the same or adjacent spaces. Portable screens or partitions and other movable items, such as planters or cabinets, are used to separate areas and divide them into a variety of different yet easily accessible work spaces.

Langdon Down’s disease

Langdon Down’s disease see Down syndrome.

Langerhans cells

Langerhans cells dendritic cells found in the epidermis. [Paul Langerhans (1847–1888), German anatomist]

language

language n. 1. a system for expressing or communicating thoughts and feelings through speech sounds or written symbols. See natural language. 2. the specific communicative system used by a particular group of speakers, with its distinctive vocabulary, grammar, and phonological system. 3. any comparable nonverbal means of communication, such as sign language or the languages used in computer programming (see artificial language).

language acquisition

language acquisition the process by which children learn language. Although often used interchangeably with language development, this term is preferred by those who emphasize the active role of the child as a learner with considerable innate linguistic knowledge.

language acquisition device (LAD)

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language acquisition support system (LASS)

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language arts

language arts the part of a school curriculum that teaches the language skills of listening, speaking, reading, writing, spelling, and handwriting.

language center

language center any area of the cerebral cortex, such as Broca’s area or Wernicke’s area, that is involved in spoken or written language.

language contact

language contact the sociolinguistic situation in which two or more language communities come into contact for reasons of geographical proximity, commerce, or politics, leading to mutual influence in lexical or structural features. See also contact language.

language death

language death the extinction of a language. The usual cause is a gradual shift to the use of another language in the younger generations of a speech community, so that the original language dies out with the older generation. In the early 21st century, it has been estimated that languages are dying out at a rate of two or three every month. By other estimates, which put the number of languages currently spoken at more than 6,000, roughly half will disappear by the end of the century. See language shift.

language deficit

language deficit an absence, loss, or delay in the normal speech and language development of a child due to some neurological dysfunction.

language delay

language delay 1. the acquisition of spoken language significantly later than is typical. The delay may or may not be symptomatic of abnormal language development. 2. a synonym for specific language impairment.

language development

language development the process by which children learn to use language. Although this term is often used interchangeably with language acquisition, it is preferred by those who wish to emphasize the continuity of language development with cognitive and social development. See also prespeech development.

language disability

language disability any significant difficulty with or impairment of language development or function. When the difficulty or impairment is restricted to a specific aspect of language development or a specific language function, it is termed specific language disability. When the difficulty or impairment is more pervasive and not restricted to a particular aspect or function, the term general language disability is used.

language disorder

language disorder see speech and language disorder.

language learning disability (LLD)

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language localization

language localization the processing of various functions of spoken and written words in particular areas of the brain. Since 1861, when Paul Broca postulated that speech processing was localized near the third frontal convolution of the left hemisphere, research has identified numerous other cortical centers associated with visual and auditory language processing, as well as neural pathways linking these areas. See Broca’s area; Wernicke’s area.

language loyalty

language loyalty a strong preference for using a minority language demonstrated by a speech community or any of its members.

language maintenance

language maintenance the continued use of the ethnic language by an immigrant or minority community across successive generations.

language pathology

language pathology see speech and language pathology.

language planning

language planning a deliberate attempt by a government to change the way a language is used by a community. A policy of raising the status of a language (status planning) is often adopted in postcolonial situations, when the new government may take steps to promote the use of indigenous languages, rather than the colonial language, in government and education. This may be accompanied by corpus planning, which refers to attempts to “improve” a language, usually by standardizing its structures, expanding or “purifying” its vocabulary, and reforming (or, in some cases, creating) its writing system.

language retardation

language retardation delayed acquisition of language skills, manifested, for example, by single-word utterances or unintelligible sounds, due to neurological causes.

language shift

language shift a movement in the language preference of an immigrant or minority community from its ethnic language to the majority language, eventually resulting in monolingualism in the majority language. See language death.

language socialization

language socialization the process by which children are socialized into the language practices, such as particular discourse routines, of the family and community.

language therapy

language therapy see speech therapy.

language transfer

language transfer in second-language acquisition, the tendency to transfer the phonology, syntax, and semantics of the native language into the learning of the second language. Negative transfer (or interference) occurs when differences between the two languages’ structures lead to systematic errors in the learning of the second language or to fossilization. Positive transfer occurs when areas of similarity between the two languages facilitate learning. See contrastive analysis; interlanguage.

language universal

language universal 1. a linguistic feature that is common to all known human languages, such as words, sentences, or (more specifically) a set of pronouns or a set of color words. Such substantive universals can be formulated on the basis of observations across multiple languages, yielding an empirically testable hypothesis that “all languages have X.” 2. in the linguistics of Noam Chomsky, a fundamental formal property that is built into the rule structure of all or nearly all language systems. An example is the rule observed by U.S. linguist Joseph H. Greenberg (1915–2001) that “In declarative sentences with nominal subject and object, the predominant order is almost always one in which the subject precedes the object.” Unlike substantive universals, these formal universals cannot be explained by universal features of human life or the physical environment. In Chomsky’s view, they constitute a universal grammar that is innate to human beings and inseparable from the language faculty itself. Also called linguistic universal; universal.

language-experience approach

language-experience approach a method of reading instruction that uses the child’s spoken language to supply the words and stories for teaching reading. In this approach, the child is encouraged to describe personal experiences, which are recorded by the teacher. They then read these written stories together until the child can associate written and spoken forms of words and read independently. [introduced in the 1960s by Roach Van Allen (d. 1998)]

language-origin theory

language-origin theory speculation about the origin and early development of language in the human species. The numerous early theories on this subject tend to fall into three main categories: (a) those that see language developing from conscious imitation by early humans of nonhuman animal noises and other natural sounds; (b) those that see it emerging from the involuntary sounds produced to express rage, pleasure, hunger, and so on; and (c) nativistic theories that see the language faculty as innate to human beings and postulate an inherent relation between sound and meaning (see phonetic symbolism). Modern research tends to ask whether language is, in fact, a uniquely human capacity and, if so, whether it evolved in response to various selective adaptations. See also species specificity of language.

languishing

languishing n. the condition of absence of mental health, characterized by ennui, apathy, listlessness, and loss of interest in life. Compare flourishing. —languish vb.

Lanterman Developmental Disabilities Act

Lanterman Developmental Disabilities Act Californian legislation, introduced in 1969, that sets forth the rights of people with developmental disabilities and the structure of the system for planning, coordinating, and delivering services and supports to them. This act is noteworthy because, unlike similar statutes in most U.S. states, it has been interpreted judicially as establishing an entitlement to services. In 1990, a class action suit (William Coffelt v. California Department of Developmental Services) criticized and challenged California’s implementation of Lanterman; the settlement agreement in 1994 (the Coffelt decision) ordered a reduction in the use of institutional settings and movement of institutional residents to community settings, along with specific changes to processes for individual planning of services and supports. The reduction in institutionalization mandated by the Coffelt decision stalled, however, and in 2001 another suit was filed challenging its implementation. The case (Capitol People First v. California Department of Developmental Services) was settled in 2009, with the Department of Developmental Services agreeing to develop, support, fund sufficiently, and publicize the existence of services to help people move from institutions to community settings.

lapsus linguae

lapsus linguae see slip of the tongue.

large-sample method

large-sample method see asymptotic method.

Lariam

Lariam n. a trade name for mefloquine.

Larodopa

Larodopa n. a trade name for levodopa.

laryngeal framework surgery

laryngeal framework surgery see thyroplasty.

laryngeal neoplasm

laryngeal neoplasm a cancerous or noncancerous growth or tumor on the larynx or any of its parts, which may affect breathing, swallowing, or speech. See phonosurgery.

laryngeal paralysis

laryngeal paralysis loss of use or feeling of one or both of the vocal cords caused by disease or injury to the nerves of the larynx.

laryngeal reflex

laryngeal reflex the reaction to laryngeal irritation manifested by coughing.

laryngectomy

laryngectomy n. the surgical removal of all or a part of the larynx, commonly because of laryngeal cancer.

laryngopharynx

laryngopharynx n. the portion of the pharynx that lies below the hyoid bone (a small, U-shaped bone below and supporting the tongue). —laryngopharyngeal adj.

larynx

larynx n. (pl. larynges) the muscular and cartilaginous structure at the top of the trachea (windpipe) and below the tongue that contains the vocal cords. Movements of the cartilages in the walls of the larynx, controlled by the laryngeal muscles, alter the tension of the vocal cords and change the frequency of the sound (thus, the pitch) emitted by the cords when they vibrate. —laryngeal adj.

LASS

LASS acronym for language acquisition support system.

Lasthénie de Ferjol syndrome

Lasthénie de Ferjol syndrome a type of pathomimicry consisting of life-threatening hemorrhages caused by secretly self-inflicted wounds. It is linked with the pathology of mourning and introjection: Patients with this disorder have all experienced traumatic losses. [named in 1967 by French hematologist Jean Bernard and colleagues after the heroine in Une histoire sans nom, a novel by French writer Jules Barbey D’Aurevilly (1808–1889)]

LAT

LAT abbreviation for Lesch’s alcoholism typology.

latah (lattah)

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latchkey children

latchkey children children who return after school to a home that is without adult supervision because their parents or caregivers work. The name alludes to the idea that the children have their own key with which to let themselves into the empty home after school. Also called self-care children.

late bilingualism

late bilingualism see early bilingualism.

late luteal phase dysphoric disorder

late luteal phase dysphoric disorder see premenstrual dysphoric disorder.

late paraphrenia

late paraphrenia any delusional disorder with onset after age 60. Late paraphrenia is used as a diagnostic entity in Europe and Britain. Also called late-onset paraphrenia.

late-onset schizophrenia

late-onset schizophrenia a psychotic state that starts after middle age (typically after age 45). It is believed that those with late-onset schizophrenia experience more positive symptoms (particularly persecutory delusions and visual, tactile, and auditory hallucinations) and fewer negative symptoms than do those with early-onset schizophrenia.

late-selection theory

late-selection theory any theory of attention proposing that selection occurs after stimulus identification. According to late-selection theory, within sensory limits, all stimuli—both attended and unattended—are processed to the same deep level of analysis until stimulus identification occurs; subsequently, only the most important stimuli are selected for further processing. Compare early-selection theory.

latency stage

latency stage in classical psychoanalytic theory, the stage of psychosexual development in which overt sexual interest is sublimated and the child’s attention is focused on skills and peer activities with members of his or her own sex. This stage is posited to last from the resolution of the Oedipus complex, at about age 6, to the onset of puberty. Also called latency; latency period; latency phase; latent stage.

latent addition period

latent addition period a brief time span when a second stimulus can add to the persisting effects of a preceding stimulus. The period varies with the size of the nerve and synaptic factors but lasts approximately 0.5 ms.

latent class analysis (LCA)

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latent construct

latent construct see latent variable.

latent content

latent content 1. the hidden or disguised meanings, wishes, and ideas beneath the manifest content of any utterance or other form of communication. 2. in psychoanalytic theory, the unconscious wishes seeking expression in dreams or fantasies. This unconscious material is posited to encounter censorship (see censor) and to be distorted by the dream-work into symbolic representations to protect the ego. Through dream analysis, the latent content may be uncovered. See also dream censorship.

latent factor

latent factor see latent variable.

latent goal

latent goal an objective of a program or organization that is not publicly stated, although it may be known to the staff. The term is also applied to functions that result from the attempt to obtain manifest goals but are not apparent or planned in advance.

latent homosexuality

latent homosexuality gay or lesbian tendencies that have never been expressed overtly; they are usually unrecognized or actively denied (i.e., repressed) by the individual. Also called unconscious homosexuality.

latent inhibition

latent inhibition retardation of classical conditioning as a result of prior exposures to a conditioned stimulus before it is paired with an unconditioned stimulus. Also called conditioned stimulus preexposure effect. Compare unconditioned stimulus preexposure effect.

latent learning

latent learning learning that is acquired without conscious effort, awareness, intention, or reinforcement and is not manifested as a change in performance until a specific need for it arises. For example, a student writing an exam may be able to cite a quotation encountered earlier accurately without having made an effort previously to learn it. Among nonhuman animals, a rat allowed to explore a maze without reward will later learn to find the goal more rapidly than a rat without prior exposure to the maze does. See also incidental learning. [first described by Edward C. Tolman]

latent need

latent need a need that is assumed to be present in a person and determines behavior but is not in that person’s conscious awareness.

latent stage

latent stage see latency stage.

latent structure analysis

latent structure analysis any of various statistical procedures that attempt to explain relationships among observed variables in terms of underlying latent variables, whether continuous or categorical. Examples include factor analysis, latent class analysis, and structural equation modeling. Also called latent structure modeling.

latent trait theory

latent trait theory a general psychometric theory contending that observed traits, such as intelligence, are reflections of more basic unobservable traits (i.e., latent traits). Several quantitative models (e.g., item response theory, factor analysis) have been developed to allow for the identification and estimation of these latent traits from manifest observations.

latent variable

latent variable a theoretical entity or construct that is used to explain one or more manifest variables. Latent variables cannot be directly observed or measured but rather are approximated through various measures presumed to assess part of the given construct. For example, suppose a researcher is interested in student conscientiousness. Because conscientiousness is a concept that cannot be directly evaluated, the researcher might develop a survey containing items pertaining to behavior indicative of conscientiousness, such as consistently attending classes, turning in assignments on time, engaging in school-sponsored fundraising activities, and so forth. Participants’ responses could then be analyzed to identify patterns of interrelationships from which the values of the latent variable of conscientiousness are inferred. Also called latent construct; latent factor. See also factor analysis; structural equation modeling.

later life adjustment

later life adjustment adaptation to stress caused by events associated with life as an older adult, including chronic disease, familial loss, and lifestyle changes.

lateral

lateral adj. toward the side of the body or of an organ. Compare medial. —laterally adv.

lateral bundle

lateral bundle a bundle of nerve fibers in the dorsolateral spinal cord that carry impulses from pain- and temperature-sensory end organs.

lateral cervical nucleus

lateral cervical nucleus a part of the lemniscal system, appearing as a small mass of gray matter beneath the medulla oblongata. Axons from the lateral cervical nucleus project to the medial lemnisci.

lateral confusion

lateral confusion see mixed laterality.

lateral corticospinal tract

lateral corticospinal tract the larger of the two subdivisions of the corticospinal tract, the other being the anterior corticospinal tract. It originates on either side of the brain, in motor areas of the cerebral cortex, and its fibers cross the midline at the pyramid of the medulla oblongata to descend laterally in the white matter on the contralateral sides of the spinal cord. The tract has an important influence on spinal motor neurons, especially those controlling fine movements of distal muscles.

lateral difference

lateral difference the difference between the two cerebral hemispheres in controlling various behaviors or serving cognitive functions.

lateral dominance

lateral dominance see dominance; hemispheric lateralization.

lateral fissure

lateral fissure see lateral sulcus.

lateral geniculate nucleus (LGN)

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lateral gyrus

lateral gyrus a convolution in the surface of the brain located in the area of the cingulate cortex above the corpus callosum.

lateral hypothalamic syndrome

lateral hypothalamic syndrome a four-stage pattern of recovery from lesions of the lateral hypothalamus induced in nonhuman animals. The first stage is marked by inability to eat and drink (aphagia and adipsia), and without assistance (including forced feeding), the animal is likely to die. The second stage includes a period of continued inability to drink and poor appetite for food (adipsia-anorexia), when only wet, palatable foods are accepted. In the third stage, the animal will eat hydrated dry food but continues to avoid water intake and may suffer dehydration. Recovery is the fourth stage, in which new, altered feeding and drinking habits are established and the animal maintains a stable, albeit lower, body weight. Compare ventromedial hypothalamic syndrome.

lateral hypothalamus (LH)

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lateral inhibition

lateral inhibition in perception, a mechanism for detecting contrast in which a sensory neuron is excited by one particular receptor but inhibited by neighboring (lateral) receptors. In vision, for example, lateral inhibition is seen in neurons that respond to light at one position but are inhibited by light at surrounding positions.

lateral lemniscus

lateral lemniscus a bundle of nerve fibers running from auditory nuclei in the brainstem upward through the pons and terminating in the inferior colliculus and medial geniculate nucleus. It is part of the lemniscal system.

lateral lisp

lateral lisp see lisp.

lateral olfactory tract

lateral olfactory tract a bundle of axons of mitral cells that forms the primary communication between the olfactory system and portions of the brain. See also olfactory tract; tufted cell.

lateral posterior nucleus

lateral posterior nucleus a group of visually responsive neurons in the thalamus that are used for brightness discrimination. They project to several areas in the occipital and parietal lobes.

lateral preoptic area (lPOA)

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lateral rectus

lateral rectus an extrinsic eye muscle that rotates the eyeball laterally (i.e., outward, away from the midline). Also called external rectus.

lateral social comparison

lateral social comparison see social comparison theory.

lateral specialization

lateral specialization the development of specialized capabilities in either the right or the left cerebral hemisphere. Examples include the tendency for speaking, writing, or calculation to involve the left hemisphere and for nonverbal ideation and spatial construction to involve the right hemisphere.

lateral spinothalamic tract

lateral spinothalamic tract see spinothalamic tract.

lateral sulcus

lateral sulcus a prominent groove that runs along the lateral surface of each cerebral hemisphere, separating the temporal lobe from the frontal lobe and parietal lobe. Also called fissure of Sylvius; lateral fissure; Sylvian fissure.

lateral thalamic nucleus

lateral thalamic nucleus either of a pair of large masses of cell bodies, one on each side of the thalamus, that relay incoming sensory impulses. The lateral nuclei are the most recently evolved parts of the thalamus.

lateral thinking

lateral thinking creative thinking that deliberately attempts to reexamine basic assumptions and change perspective or direction to provide a fresh approach to solving a problem. This term is often used synonymously with divergent thinking. [defined by British psychologist Edward de Bono (1933– )]

lateral ventricle

lateral ventricle a chamber of complex shape that lies within each cerebral hemisphere in the brain and serves as a reservoir of cerebrospinal fluid (see ventricle). Each lateral ventricle communicates with the third ventricle at a point near the thalamus.

lateral-line system

lateral-line system a sensory system, found in many kinds of fish and some amphibians, that informs the animal of water motion in relation to the body surface.

laterality

laterality n. the preferential use of one side of the body for certain functions, such as eating, writing, and kicking. See also handedness; mixed laterality.

lateralization

lateralization n. 1. one-sided preferences, such as handedness, eye dominance, and footedness. Observed more frequently in humans than in other primates, lateralization is manifested in the way tasks are performed and can also be inferred from the effects of localized brain damage. Directional confusion and dyslexia may be diagnosed through lateralization tests. See also hemispheric lateralization; speech lateralization. 2. in audition, see auditory localization.

lateralized readiness potential (LRP)

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lateropulsion

lateropulsion n. a symptom of certain disorders of the central nervous system (e.g., parkinsonism) in which the individual makes involuntary sidewise movements.

lateroventral nucleus

lateroventral nucleus one of a group of relay nuclei in the thalamus that transmit impulses from the cerebellum to the motor cortex for coordination of muscular movements. Also called ventral lateral nucleus.

Latin square

Latin square a type of within-subjects design in which treatments, denoted by Latin letters, are administered in sequences that are systematically varied such that each treatment occurs equally often in each position of the sequence (first, second, third, etc.). The number of treatments administered must be the same as the number of groups or individual participants receiving them. For example, for an experimental design involving four treatments (A, B, C, and D) and four people, one person might receive Treatment A, then B, then C, and then D; a second person might receive them in sequence B, C, D, and A; a third person in sequence C, D, A, and B; and a fourth person in sequence D, A, B, and C. It is important to note that although Latin squares control for order effects they do not control for carryover effects or practice effects. See also balanced Latin square; Graeco-Latin square.

latitude of acceptance

latitude of acceptance in social judgment theory, a range of attitudinal positions that includes a person’s preferred position and the range of positions that he or she considers acceptable. See also latitude of noncommitment; latitude of rejection.

latitude of noncommitment

latitude of noncommitment in social judgment theory, a range of attitudinal positions that a person considers to be neither acceptable nor objectionable. See also latitude of acceptance; latitude of rejection.

latitude of rejection

latitude of rejection in social judgment theory, a range of attitudinal positions that a person rejects. See also latitude of acceptance; latitude of noncommitment.

lattah

lattah n. see latah.

Latuda

Latuda n. a trade name for lurasidone.

laudanum

laudanum n. a mixture of alcohol and opium once commonly used as an analgesic and anesthetic. The mixture was introduced around 1530 by German alchemist and physician Paracelsus (1493–1541) and was widely consumed in 18th-century England.

laughing gas

laughing gas see nitrous oxide.

laughter

laughter n. vocal expression of amusement, enjoyment, or derision, characterized by inspiratory and expiratory movements occurring in rapid succession. Laughter is pleasurable because it serves to release tension built up when people listen to an amusing story or watch an amusing event (see release theory of humor). Laughter may also result when states of threat occur in a safe context (see arousal jag) or from an abrupt resolution of a cognitive incongruity. In psychoanalytic theory, laughter may be viewed as a defense against crying or embarrassment. Unrestrained or paroxysmal laughing spells have been found to precipitate cataplectic attacks, to be a common manifestation in manias, and to be an occasional symptom of psychomotor seizures among children. Spasmodic laughter, or gelasmus, is also found in schizophrenia, hysteria, and organic (especially bulbar and pseudobulbar) diseases of the brain, as well as in choreomania. See also humor. —laugh vb.

Launois–le Cleret syndrome

Launois–le Cleret syndrome see Fröhlich’s syndrome.

Laurence–Moon–Bardet–Biedl syndrome

Laurence–Moon–Bardet–Biedl syndrome an autosomal recessive disorder first described in 1866 by British ophthalmologist John Zachariah Laurence (1830–1870) and his colleague, British-born U.S. ophthalmologist Robert C. Moon (1844–1914), in four siblings with progressive visual impairment, obesity, paralysis, and cognitive impairment. In 1920 and 1922, respectively, French physician George Bardet (1885–1970) and Romanian-born Austrian physician Artur Biedl (1869–1933) independently described patients sharing only some of the symptoms seen in the original siblings, plus additional symptoms that they did not exhibit (e.g., polydactyly, impaired speech, hypogonadism). The syndrome was thus divided into two related disorders, Laurence–Moon syndrome and Bardet–Biedl syndrome (BBS). However, because of overlapping phenotypes, it is thought to be one syndrome, with BBS being the term now commonly used to cover both syndromes. Also called Laurence–Moon–Biedl–Bardet syndrome.

law

law n. 1. a formal statement describing a regularity (e.g., of nature) to which no exceptions are known or anticipated. See causal law; natural law. 2. in science, mathematics, philosophy, and the social sciences, a theory that is widely accepted as correct and that has no significant rivals in accounting for the facts within its domain. 3. a formally established rule regulating the conduct of people within a particular jurisdiction that must be obeyed to avoid legal sanctions.

law of advantage

law of advantage the principle that one of two or more incompatible or inconsistent responses has the advantage of being more beneficial or attractive and therefore occurs more frequently than the others.

law of assimilation

law of assimilation 1. the principle that organisms respond to new situations in a manner similar to their reactions to familiar situations. See generalization. 2. see assimilation.

law of closure

law of closure see closure.

law of combination

law of combination the principle that (a) two or more stimuli occurring simultaneously or in proximity may produce a combined response and (b) that two responses may occur together when a stimulus eliciting either of them is presented.

law of common fate

law of common fate see common fate.

law of common region

law of common region see common region.

law of constancy

law of constancy 1. the principle that visual stimuli retain a constant appearance despite alterations in stimulus conditions, such as the level of illumination (brightness constancy) or the angle subtended on the retina (size constancy). 2. in psychoanalytic theory, see principle of constancy.

law of contiguity

law of contiguity a principle of association stating that forming connections between ideas, events (e.g., stimuli and responses), or other items depends on their proximity in space or time. It has been supplemented by the principle of contingency; that is, the degree of association between events increases when the probability of one event occurring is increased by the occurrence of the other. The combination of contiguity and contingency is now viewed as essential to forming associations and is a keystone of most contemporary theories of learning, memory, and knowledge.

law of continuity

law of continuity see good continuation.

law of contrast

law of contrast a principle of association stating that opposites are reminders of one another: encountering or thinking about one (e.g., a snow-covered field) tends to bring to mind the other (e.g., a sunny beach). Initially proposed as a distinct, essential concept in associationism, the law of contrast later came to be viewed as a special case of the law of contiguity.

law of disuse

law of disuse see law of use.

law of effect

law of effect broadly, the principle that consequences of behavior act to modify the future probability of occurrence of that behavior. As originally postulated by Edward L. Thorndike, the law of effect stated that if a response R produces a satisfying state of affairs (or a positive reinforcer), then an association is formed between R and the stimuli S present at the time R was made. As a result of this S–R association, R occurs whenever the organism encounters S. This part of the law of effect was the foundation of S–R theories of learning. Originally, Thorndike also proposed that the presentation of an aversive or annoying consequence serves to weaken S–R associations, with the consequence that responding becomes suppressed. He later revised the law to include only the response-strengthening effect of reinforcement; the original version of the law was called the strong law of effect, and the revised version was known as the weak law of effect.

law of equality

law of equality a gestalt principle that parts of a figure perceived as equal tend to form a whole.

law of equipotentiality

law of equipotentiality see equipotentiality.

law of exercise

law of exercise the principle that repetition of some act makes that act more probable in the future. The law of exercise was first suggested and then discarded by Edward L. Thorndike.

law of filial regression

law of filial regression the principle that inherited traits tend to revert toward the mean for the species; for example, very tall fathers tend to have sons shorter than themselves but taller than the population mean, and very short fathers tend to have sons taller than themselves but shorter than the population mean.

law of forward conduction

law of forward conduction the rule that, under natural conditions, nerve impulses always travel in the same direction, from the axon hillock, where the axon originates at the cell body, to the terminal button of the axon. Also called forward-conduction law. Compare antidromic conduction.

law of frequency

law of frequency a principle of association stating that the more often ideas, events (e.g., stimuli and responses), or other items co-occur, the stronger the connections between them. The law of frequency is a concept of associationism.

law of good continuation

law of good continuation see good continuation.

law of good figure

law of good figure the principle of Prägnanz as applied to vision. It states that any pattern is perceived so that the resulting figure is as simple as possible.

law of good shape

law of good shape see good shape.

law of inclusiveness

law of inclusiveness see inclusiveness.

law of initial values

law of initial values the principle that the initial level of a physiological response is a major determinant of a later response in that system. Thus, if an individual’s pulse rate is high, his or her cardiovascular response to an emotion-provoking stimulus will be weaker than if the initial pulse rate had been low. Also called initial value dependency; initial values law; rate dependence effect. See rate dependency. [proposed in 1931 by U.S. neuropsychiatrist Joseph Wilder (1895–1976)]

law of large numbers

law of large numbers a mathematical principle indicating that as the sample size increases, the theoretical expectations of its statistical properties will be more and more closely realized. For example, as the number of replications of an experiment increases, the average (mean) of the observed results will approach the true average (theoretical probability in the population) with increasing accuracy. According to the strong law of large numbers, the average of the results obtained from a large number of trials will converge upon the theoretically expected value, becoming closer as more trials are performed. In distinction, the weak law of large numbers states that the average is likely to converge upon the expected value as more trials are conducted. Thus, the essential difference between the two laws is that the former insists on convergence whereas the latter expects convergence.

law of least action

law of least action see principle of least effort.

law of mass action

law of mass action see mass action.

law of neurobiotaxis

law of neurobiotaxis the principle that dendrites of developing neurons grow in the direction of the axons of nearby active neurons. See neurobiotaxis.

law of parsimony

law of parsimony the principle that the simplest explanation of an event or observation is the preferred explanation. Simplicity is understood in various ways, including the requirement that an explanation should (a) make the smallest number of unsupported assumptions, (b) postulate the existence of the fewest entities, and (c) invoke the fewest unobservable constructs. Also called economy principle; principle of economy; principle of parsimony. See elegant solution; Occam’s razor.

law of Prägnanz

law of Prägnanz see Prägnanz.

law of precision

law of precision in Gestalt psychology, the principle that all percepts tend to become organized into regular, symmetrical forms with precise contours. The term is used occasionally as a synonym for the principle of Prägnanz.

law of primacy

law of primacy see primacy effect.

law of prior entry

law of prior entry the principle that when two stimuli are presented simultaneously, one attended to and the other not, the attended stimulus will be perceived as having occurred before the other. See complication experiment.

law of proximity

law of proximity see proximity.

law of recency

law of recency see recency effect.

law of similarity

law of similarity 1. a principle of association stating that like produces like: Encountering or thinking about something (e.g., one’s birthday month) tends to bring to mind other similar things (e.g., other people one knows with the same birthday month). The law of similarity is fundamental to associationism. 2. see similarity.

law of specific nerve energies

law of specific nerve energies see specific-energy doctrine.

law of sufficient reason

law of sufficient reason the proposition, introduced by Gottfried Wilhelm Leibniz, that if something exists, it is necessarily the case that there is sufficient reason for its existence. The principle implies an inherent rationale for the universe. It is complemented by Leibniz’s law of insufficient reason, which states that if there is not sufficient reason for the existence of something, it will not exist.

law of symmetry

law of symmetry see symmetry.

law of use

law of use the principle that the more an association is used, the stronger it becomes. The complementary law of disuse states that the less an association is used, the weaker it becomes. Both laws were first suggested and then discarded by Edward L. Thorndike.

law-and-order orientation

law-and-order orientation see conventional level.

laws of grouping

laws of grouping see gestalt principles of organization.

laws of learning

laws of learning statements describing the circumstances under which learning generally occurs. Over the centuries, such laws have been hypothesized and studied by philosophers such as Aristotle, John Locke, and John Stuart Mill and physiologist Ivan Pavlov, among others: The modern laws of learning were formalized in 1911 by Edward L. Thorndike and have been modified numerous times since. Among the currently accepted laws of learning are the law of effect, the law of contiguity, the law of frequency, the primacy effect, and the recency effect.

laws of thought

laws of thought certain principles of logic, such as the identity principle, that are deemed to be so essential to rational thought as to assume the character of law. Indeed, such principles define the very idea of logical thought. Which logical principles should be included in a set of such laws is, however, a matter of debate.

laxative addiction

laxative addiction a dependence on the use of laxatives to induce bowel movements. The addiction is a vicious cycle, in which the use of laxatives gradually reduces bowel activity so that further use becomes the only way to avoid constipation. Laxative addiction is often associated with eating disorders in which laxatives are routinely used for purging. See also enema addiction; klismaphilia.

lay analysis

lay analysis historically, psychoanalytic therapy performed by a person who had been trained in psychoanalytic theory and practice but was not a physician (i.e., a layperson). Beginning in the 1950s, psychoanalytic training institutions began training licensed mental health practitioners besides psychiatrists, including psychologists and social workers, thus rendering the term obsolete.

lay psychology

lay psychology see naive analysis of action.

layperson personality theories

layperson personality theories see naive personality theories.

lazy eye

lazy eye see amblyopia.

LBW

LBW abbreviation for low birth weight.

LCA

LCA abbreviation for latent class analysis.

LCU

LCU abbreviation for life-change unit.

LD

LD 1. abbreviation for learning disability. 2. abbreviation for learning disorder. 3. abbreviation for lethal dose.

LDH

LDH abbreviation for lactate dehydrogenase.

LE

LE abbreviation for lupus erythematosus.

lead-pipe rigidity

lead-pipe rigidity muscular rigidity that produces a smooth, steady resistance to passive movement of the limbs of people with parkinsonism or cerebral palsy. Compare cogwheel rigidity.

leader

leader n. 1. an individual who guides others in their pursuits, often by organizing, directing, coordinating, and motivating their efforts. 2. an individual of authority in a social group or organization, such as the head of a university department or a military commander. 3. one who is thought to possess the qualities or characteristics associated with individuals who rise to positions of authority in groups and organizations. See also leadership.

leader categorization theory

leader categorization theory an information-processing model that assumes that perceivers automatically and spontaneously appraise the extent to which people, including themselves, can be classified as leaders. Such judgments are determined by implicit leadership theories that organize perceivers’ general beliefs about the characteristics that most leaders possess. See also attribution theory of leadership; leader prototype.

leader match

leader match an approach to leadership training based on the contingency theory of leadership of Fred Fiedler. It proposes (a) that effective leadership is dependent on a match between the individual’s leadership style and the particular group situation and (b) that individuals usually find it difficult to alter their established style of leadership but (c) that leaders can be trained to diagnose a situation and alter it to fit their own style.

leader prototype

leader prototype a cognitive representation of an actual or abstract leader who is thought to possess features shared by most or all individuals considered to be leaders and so to exemplify that construct. See also attribution theory of leadership; leader categorization theory.

leader–member exchange theory (LMX theory)

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leaderless group discussion

leaderless group discussion an exchange of opinions, ideas, and information on some topic by the members of a group with no identified leader. Such discussions are used in studies of group productivity and leadership emergence to evaluate specific interpersonal and leadership skills; in training and educational settings to provide participants with insights into their own and others’ behaviors in open, unstructured group situations; and in screening candidates for positions in business, social work, teaching, and the military.

leaderless group therapy

leaderless group therapy a form of group therapy in which leaderless meetings are held either (a) on an occasional or regularly scheduled basis as an adjunct to the traditional therapist-led process or (b) on an entirely self-directed basis in which a group always meets without a designated leader.

leadership

leadership n. 1. the processes involved in leading others, including organizing, directing, coordinating, and motivating their efforts toward achieving certain group or organizational goals. Leadership tends to be reciprocal (leaders influence followers, and followers influence leaders), transactional (leaders and followers exchange their time, energies, and skills to increase their joint rewards), transformational (leaders inspire and motivate followers), and cooperative rather than coercive (followers voluntarily accept the leader’s suggestions). See transactional leadership; transformational leadership. 2. the traits or behaviors characteristic of an effective leader. See leadership theories.

leadership emergence

leadership emergence the process by which an individual is recognized (formally or informally, perceptually or behaviorally, implicitly or explicitly) as the leader of a formerly leaderless group. See emergent leader.

leadership labyrinth

leadership labyrinth a metaphor for the series of detours, dead ends, and unusual paths that women and members of minority groups encounter in many organizations and that serve as obstacles to reaching the highest positions of authority. For women, these obstacles include not only sex discrimination but also domestic responsibilities (see mommy track) and sometimes women’s own doubts and failure to believe in themselves. Compare glass ceiling. [proposed in 2007 by U.S. social psychologists Alice H. Eagly (1938– ) and Linda L. Carli]

leadership role

leadership role 1. structurally, the position occupied by the person who is responsible for guiding others in their pursuits. 2. behaviorally, a relatively coherent set of task and relationship behaviors expected of the individual who is formally or informally identified as a group’s leader.

leadership style

leadership style 1. the stable behavioral tendencies and methods displayed by a particular leader when guiding a group. Common styles include those of autocratic leaders (see authoritarian leader), bureaucratic leaders, charismatic leaders, democratic leaders, and laissez-faire leaders. 2. in style and contingency leadership theories, the extent to which the leader’s approach can be characterized as task motivated and relationship motivated. Most such theories argue that effective leaders balance these two basic orientations in the groups they lead. See also Least Preferred Coworker Scale.

leadership substitute

leadership substitute any aspect of the social setting, including the nature of the work task, the characteristics of the group members, or the qualities of the group or organization itself, that reduces or eliminates the need for a specific individual who performs such typical leadership behaviors as organizing, directing, coordinating, supporting, and motivating the group members.

leadership theories

leadership theories theories advanced to explain the effectiveness or ineffectiveness of leaders. The main types include trait theories of leadership, which focus on such characteristics as supervisory ability, intelligence, self-assurance, and decisiveness; behavioral theories of leadership, which focus on the task-based and relationship-based activities of the leader; contingency theories of leadership, which attempt to describe what type of leadership style is most effective in different situations; and cognitive theories of leadership, such as leader categorization theory or the attribution theory of leadership, which describe the way subordinates’ perceptions of their leaders influence leadership effectiveness. See also implicit leadership theories.

leaf node

leaf node see graph; tree.

leaf switch

leaf switch a nonrigid, flexible lever switch that is activated by a slight bending, enabling it to be operated by a user with a disability.

leakage

leakage n. the unintended revelation that a person has a feeling or motive different from the one intended to be communicated to others. It may be manifested, for example, by frequent speech pauses when a person describes an event untruthfully. See verbal leakage. See also deception clue.

lean medium

lean medium see media richness.

learned helplessness

learned helplessness a phenomenon in which repeated exposure to uncontrollable stressors results in individuals failing to use any control options that may later become available. Essentially, individuals are said to learn that they lack behavioral control over environmental events, which, in turn, undermines the motivation to make changes or attempt to alter situations. The phenomenon was first described in 1967 by U.S. psychologists J. Bruce Overmier (1938– ) and Martin E. P. Seligman (1942– ) after experiments in which nonhuman animals exposed to a series of unavoidable electric shocks later failed to learn to escape these shocks when tested in a different apparatus, whereas animals exposed to shocks that could be terminated by a response did not show interference with escape learning in another apparatus. A syndrome with three features developed: (a) a motivational deficit characterized by a failure to respond when challenged with further aversive events, (b) an associative deficit characterized by impairment of learning from successful coping, and (c) an emotional deficit characterized by apparent underreactivity to painful events—although later research revealed by assaying corticoid levels that the animals were very stressed. In the 1970s, Seligman extended the concept from nonhuman animal research to clinical depression in humans and proposed a learned helplessness theory to explain the development of or vulnerability to depression. According to this theory, people repeatedly exposed to stressful situations beyond their control develop an inability to make decisions or engage effectively in purposeful behavior. Subsequent researchers have noted a robust fit between the concept and posttraumatic stress disorder.

learned optimism

learned optimism an explanatory style that attributes causes for negative events to factors that are external, unstable, and specific: That is, problems are believed to be caused by other people or situational factors, the causes are seen as fleeting in nature, and they are localized to one or a few situations in one’s life. According to learned helplessness theory, the manner in which individuals routinely explain the events in their lives can drain or enhance motivation, reduce or increase persistence, and enhance vulnerability to depression or protect against it, making learned optimism a putative mechanism by which therapy ameliorates depression.

learned response

learned response see acquired response.

learned taste aversion

learned taste aversion see conditioned taste aversion.

learned treatise exception

learned treatise exception an exception to the hearsay rule (which states that evidence from statements by individuals other than the testifying individual is inadmissible in court) that allows expert witnesses to speak for others if they are reporting an opinion shared by the experts in their field. Therefore, an expert may report findings contained in journal articles or similar published treatises for the purpose of informing the court of the general expert opinion concerning the matter in question. See also opinion testimony.

learning

learning n. the acquisition of novel information, behaviors, or abilities after practice, observation, or other experiences, as evidenced by change in behavior, knowledge, or brain function. Learning involves consciously or nonconsciously attending to relevant aspects of incoming information, mentally organizing the information into a coherent cognitive representation, and integrating it with relevant existing knowledge activated from long-term memory.

Learning Abilities Measurement Program (LAMP)

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learning by doing

learning by doing see progressive education.

learning center

learning center 1. an educational technique in which skill-specific sets of activities are developed for students to work on independently at their own pace for a particular length of classroom time during each school day. For example, a kindergarten teacher may create a center for counting, where students color shapes numbered 1 through 10 and then glue them in sequence onto a piece of construction paper; a center for vocabulary, where students illustrate their own personal dictionaries with pictures that correspond to the words; and a center for fine motor skills, where students trace an animal from a pattern and then cut out and decorate it. During learning center time, students are divided into small groups that each have a different task to complete, with the tasks periodically rotating among the groups. Commonly seen in the elementary-school grades, such self-directed learning is intended to demonstrate or strengthen skills with which students already are familiar rather than to facilitate the acquisition of new skills. 2. more generally, any educational establishment or program that facilitates students’ acquisition of knowledge or understanding of topics by providing additional support and personalized instruction outside of regular school hours. Learning centers may be government funded or privately funded, and they may be offered within existing community or educational facilities, in stand-alone facilities, or online. They serve a range of ages and populations, such as gifted children; adolescents with learning disabilities, emotional difficulties, or behavioral problems; and adult professionals seeking further training. The specific tools and materials available vary by facility or program but generally include enrichment and recreational activities, tutoring, computer and Internet practice, counseling, and other services. Also called learning support center.

learning curve

learning curve a graphic representation of the course of learning of an individual or a group. A measure of performance (e.g., gains, errors) is plotted along the vertical axis; the horizontal axis plots trials or time. Also called acquisition curve. See negative acceleration; positive acceleration.

learning difficulties

learning difficulties in the United Kingdom, intellectual disability or learning disability.

learning disabilities specialist

learning disabilities specialist an individual, usually working within an interdisciplinary team of school professionals, who is trained to identify and assist students with problems associated with learning disabilities.

learning disability (LD)

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learning disorder (LD)

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learning goal

learning goal in the analysis of personality and goal-directed motivation of U.S. personality psychologist Carol S. Dweck (1946– ), a goal to acquire mastery of a task or subject matter. Also called mastery goal.

learning model

learning model a general perspective on human development in which children are viewed as passively absorbing the relevant features of the environment in a continuous line of development. This emphasis on environmental conditions is less influential within developmental psychology than previously, rapidly being eclipsed by the lifespan perspective and other approaches.

learning paradigm

learning paradigm an experimental design used to research incidental learning. Groups of participants are shown the same stimuli (e.g., a list of 20 words) but asked to perform different tasks with them (e.g., picture associated words, determine the average number of letters in each word). Afterward, the participants unexpectedly are asked to recall as many of the presented items as possible.

Learning Potential Assessment Device (LPAD)

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learning set

learning set a phenomenon observed when a participant is given a succession of discrimination problems to learn, such as learning that one object contains a food reward and a different object does not. After a large number of such problems, the participant acquires a rule or mental set for solving them, and successive discriminations are learned faster. See learning to learn. [introduced in 1949 by Harry Harlow]

learning skills

learning skills the abilities involved in gathering knowledge and increasing understanding, especially those abilities demonstrated in educational settings and developed through study, classroom instruction, and the like.

learning strategy

learning strategy a mental or behavioral approach or method used to facilitate learning, such as forming a mental image, organizing items, searching for existing associations, or practicing retrieval.

learning style

learning style see cognitive style.

learning support center

learning support center see learning center.

learning technologies

learning technologies electronic tools or advanced machines used to facilitate learning, such as film, television, computers, and the Internet. Web-based instruction plays a growing role in modern distance learning.

learning theory

learning theory a body of concepts and principles that seek to explain the learning process. Learning theory actually encompasses a number of specific theories whose common interest is the description of the basic laws of learning, usually derived from studies of classical and instrumental conditioning and verbal learning. These include Hull’s mathematico-deductive theory of learning, the purposive behaviorism of Edward C. Tolman, the Rescorla–Wagner theory, and the comparator hypothesis, among others.

learning to learn

learning to learn 1. repeated practice with one kind of task but learning different material each time, which facilitates the ability to learn new material. Harry Harlow demonstrated learning to learn by teaching monkeys to discriminate between pairs of objects. The animals eventually became skilled at rapidly learning new discriminations, sometimes in a single trial. See learning set; transfer of training. 2. acquiring effective learning strategies such as planning; goal-setting; scheduling; using mnemonics, outlines, and flashcards; and monitoring progress.

learning trial

learning trial a single presentation of the information to be learned in a learning experiment. Examples of learning trials are a single pairing of the conditioned stimulus and the unconditioned stimulus in classical conditioning and a single presentation of a word to be remembered in a memory experiment. The amount of learning is typically expressed as a function of the number of learning trials given, as in a learning curve. Also called acquisition trial.

learning types

learning types individual differences in people’s preferred ways of organizing and processing information (see cognitive style). For example, some people may prefer to remember auditory information and develop strategies to recall verbal information; others may prefer visual and imaginal coding of material.

learning without awareness

learning without awareness a phenomenon said to occur when an individual’s behavior has been affected without that individual being aware of the conditions affecting the behavior, of the relationship between those conditions and the behavior, or of the fact that the behavior has changed. The existence of such learning is controversial but evidence has been found in classical conditioning, procedural learning, implicit learning, and subliminal learning. However, the critical data for assessing awareness depend on experimental participants’ verbal reports that they are unable to describe the learning experience to which they were exposed.

least effort principle

least effort principle see principle of least effort.

least perceptible duration

least perceptible duration see just noticeable duration.

Least Preferred Coworker Scale (LPC Scale)

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least restrictive alternative

least restrictive alternative the U.S. legal directive that less treatment rather than more (e.g., community care vs. hospitalization) is the most desirable objective in treating people with a chronic mental disorder. The principal consideration is combining safety concerns with the minimum level of restrictions on personal liberty. This position was emphasized in two decisions of U.S. Court of Appeals Judge David L. Bazelon (1910–1993) in 1966: Rouse v. Cameron and Lake v. Cameron.

least restrictive environment (LRE)

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least significant difference (LSD)

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least squares criterion

least squares criterion in regression analysis and similar statistical procedures, the principle that one should estimate the values of parameters in a way that will minimize the squared error of predictions from the model. That is, one should strive to build models that minimize the squared differences between actual scores (observed data) and expected scores (those predicted by the model). Also called least squares principle.

least squares regression

least squares regression a type of regression analysis in which the researcher strives to develop a least-squared-errors solution or least squares solution to describe the relationship between an outcome or dependent variable and one or more predictors or independent variables. That is, one develops a model that is the best fit for the data because it yields the smallest squared differences between the actual observations and their values as predicted by the model. Also called least squares estimation; ordinary least squares (OLS) regression. See least squares criterion.

leaving the field

leaving the field the act of removing oneself from a situation when confronted with seemingly insurmountable obstacles, insoluble conflicts, or intensely frustrating problems. It may involve physical withdrawal, escape into psychogenic illness, or some other behavior, such as distraction or changing the subject during a conversation.

Leber’s disease

Leber’s disease a hereditary visual disorder characterized by slowly progressive optic atrophy with normal peripheral vision but blind areas of the retina toward the center. The genetic defect is transmitted by females, but males are most often affected, with symptoms beginning around the third decade of life. Also called Leber’s optic atrophy. See also amaurosis. [Theodor Leber (1840–1917), German ophthalmologist]

Leboyer technique

Leboyer technique an approach to childbirth that focuses on the feelings and sensations of the baby. It advocates quiet, dim lights, delay in severing the umbilical cord; body contact between newborn and parents, and an immediate warm bath that approximates the conditions within the womb. See also Lamaze method. [Frédéric Leboyer (1918– ), French obstetrician]

lecanomancy

lecanomancy n. a system of divination in which a sensitive or clairvoyant looks into a basin, bowl, or vase of water, often after rocks have been dropped in or oil has been added, and sees alleged visions of the future or interprets the observed patterns or ripples. —lecanomancer n.

Lectopam

Lectopam n. a trade name for bromazepam.

lecture method

lecture method the formal, verbal presentation of information or other material by an instructor to a group of students or other learners. The lecture method is used mainly when groups are large or time is limited (e.g., in personnel training). It can also be used to introduce other instructional methods, such as audiovisual presentations or role play, or to summarize material developed by other means.

Lee–Boot effect

Lee–Boot effect a prolonged diestrus phase, induced by pheromones, that occurs when a female animal is housed with other females. [first reported in 1955 by S. van der Lee and L. M. Boot, Dutch biologists]

left brain

left brain the left cerebral hemisphere of the brain. The term is sometimes used to describe functions or cognitive style supposedly mediated by the left (rather than by the right) hemisphere, such as analytical thinking. Compare right brain. See also hemispheric lateralization.

left censoring

left censoring the situation in which a researcher cannot determine the precise time at which a target event occurred for some individuals within a sample because those participants experienced the event prior to the observation period. For example, left censoring might arise in a study of alcohol initiation among high school students because a subset of the sample is likely to have initiated use prior to high school entry. See also right censoring.

left hemisphere

left hemisphere the left half of the cerebrum, the part of the brain concerned with sensation and perception, motor control, and higher level cognitive processes. The two cerebral hemispheres differ somewhat in function; for example, in most people, the left hemisphere has greater responsibility for speech. See hemispheric encoding–retrieval asymmetry; hemispheric lateralization. Compare right hemisphere.

left-handedness

left-handedness n. the preferential use of the left hand for major activities, such as eating, writing, and throwing. See also laterality; sinistrality. Compare right-handedness.

left-hemisphere consciousness

left-hemisphere consciousness the claim by U.S. cognitive neuropsychologist Michael S. Gazzaniga (1939– ) that the “speaking hemisphere” of the brain (the left hemisphere in most people) is the seat of consciousness. Others, including Roger Sperry, have proposed that the right hemisphere may also have its own form of consciousness. See right-hemisphere consciousness.

legal blindness

legal blindness see blindness.

legal capacity

legal capacity the ability to acquire the knowledge and understanding necessary to make a rational choice regarding any issue that has legal implications (e.g., entering into contracts, making a will, standing trial). See also competency to stand trial.

legal psychiatry

legal psychiatry see forensic psychiatry.

legal psychology

legal psychology see forensic psychology.

legal testimony

legal testimony evidence given by an individual in court under oath or affirmation, either orally or in a written affidavit. Written evidence that was obtained during a deposition (an official pretrial questioning of an individual) may also be presented as testimony.

legasthenia

legasthenia n. a controversial syndrome in which the primary symptom is difficulty in synthesizing letters into words and analyzing words by breaking them down into their component letters, despite adequate intellectual and perceptual ability.

legend

legend n. 1. a traditional story that has been passed down from an earlier period and may or may not contain elements of historical truth. Legends usually grow by a process of chain reproduction. See also mythology. 2. a caption or key that explains illustrations or symbols on a graph, map, or chart. —legendary adj.

legibility

legibility n. 1. capability of being read or deciphered. 2. the ease with which an environment can be cognitively represented, which determines one’s ability to navigate or find one’s way within an environment or setting. Landmarks, the overall shape or configuration of street grids, and building layout can significantly influence legibility. See also cognitive map; environmental cognition. —legible adj.

legitimate authority

legitimate authority see authority.

legitimate power

legitimate power a capacity to influence others that is based on the influencer’s position or role in the group and members’ recognition that an individual in such a position has the right to require and demand compliance with his or her directives.

leisure lifestyle

leisure lifestyle a way of life in which leisure and free time play a prominent role. Leisure activities (e.g., hobbies, recreation, self-selected activities) largely or entirely replace obligatory activities (e.g., work for pay), as is the case for people who have retired from full-time paid employment.

Lejeune syndrome

Lejeune syndrome see cri du chat syndrome.

lek mating

lek mating a mating system in which several males congregate at one location during the mating season, forming small individual territories and competing with each other for mates by giving complex, elaborate visual and vocal displays. Females are attracted by these displays and move among the males to choose their mate. Typically, the males provide no parental care to resulting offspring.

lemma

lemma n. 1. in logic, a subsidiary proposition used as a part of the proof of a subsequent proposition. The proof of the lemma may or may not be included in the argument. 2. in linguistics, a word considered to be the word in its basic dictionary form together with all of its inflected forms. For example, the lemma be consists of be plus am, are, is, was, were, being, and been.

lemniscal system

lemniscal system a major somatosensory system consisting of long, ascending neural pathways projecting to the thalamus. It includes the medial lemniscus, lateral lemniscus, and secondary trigeminal projections.

length of stay (LOS)

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leniency error

leniency error a type of rating mistake in which the ratings are consistently overly positive, particularly regarding the performance or ability of the participants. It is caused by the rater’s tendency to be too positive or tolerant of shortcomings and to give undeservedly high evaluations. Also called leniency bias. Compare severity error.

lens

lens n. 1. in vision, a transparent, biconvex structure in the anterior portion of the eyeball (just behind the iris) that provides the fine, adjustable focus of the optical system. It is composed of tiny hexagonal prism-shaped cells, called lens fibers, fitted together in concentric layers. 2. an artificial enhancer to the eyes’ natural structure, made of glass or plastic, that serves to focus vision (e.g., eyeglasses or contact lenses).See accommodation.

lens model

lens model a metaphorical model intended to characterize the fact that organisms do not perceive the environment directly and objectively but instead use available cues to make inferences, judgments, or interpretations of the environment. A variety of cues are available, and the organism selects those it will use and then assigns each a relative weight or importance in the interpretive process. [proposed by Egon Brunswik]

lenticular nucleus

lenticular nucleus see basal ganglia.

Leonardo’s paradox

Leonardo’s paradox the apparent curvature of straight elements at the margins of a wide-angle scene containing linear perspective. [Leonardo da Vinci (1452–1519), Italian artist and scientist]

leptin

leptin n. a protein, manufactured and secreted by fat cells, that may communicate to the brain the amount of body fat stored and may help to regulate food intake. Leptin receptors have been found in the hypothalamus, and, when they are stimulated, food intake is reduced.

leptokurtic

leptokurtic adj. describing a frequency distribution that is more peaked than the normal distribution, having more scores in the center and fewer at the two extremes. See also mesokurtic; platykurtic.

leptomorph

leptomorph n. see body-build index.

leptosome type

leptosome type see asthenic type.

LEQ

LEQ abbreviation for Lifetime of Experiences Questionnaire.

LES

LES abbreviation for local excitatory state.

lesbian feminism

lesbian feminism a type of feminism that emphasizes the sociopolitical meaning of lesbianism. Beyond the implications that lesbianism may have for women’s right to control their own sexuality, it is suggested that lesbianism is the ultimate rejection of patriarchy. See also lesbian separatism.

lesbian separatism

lesbian separatism a radical form of lesbian feminism arguing that feminist women should reject heterosexuality to effect a complete separation from patriarchal society and its institutions.

lesbianism

lesbianism n. female–female sexual orientation or behavior. The name is derived from Lesbos, an Aegean island where the poet Sappho (c. 600 bce) wrote glowing accounts of erotic activities between women. Formerly called Sapphism. See also homosexuality. —lesbian adj., n.

Lesch–Nyhan syndrome

Lesch–Nyhan syndrome an X-linked recessive disorder associated with deficiency of the enzyme hypoxanthine–guanine phosphoribosyltransferase, which leads to overproduction of uric acid. Affected individuals have severe kidney problems; moderate cognitive disabilities; and a compulsive, self-mutilating tendency to bite their lips and fingers. Motor development deteriorates after the first 6 to 8 months of life, marked by spasticity, chorea (involuntary jerky movements), and athetosis (sinuous involuntary movements). Also called hereditary choreoathetosis; hereditary hyperuricemia. [described in 1964 by Michael Lesch (1939–2008) and William L. Nyhan (1926– ), U.S. pediatricians]

Lesch’s alcoholism typology (LAT)

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lesion

lesion n. any disruption of or damage to the normal structure or function of an organ or part of an organ due to injury, disease, or a surgical procedure. A lesion may be a wound, ulcer, tumor, cataract, or any other pathological change in tissue. See also temporary lesion.

less-is-more hypothesis

less-is-more hypothesis the proposition that the cognitive limitations of infants and young children may serve to simplify the body of language they process, thus making it easier for them to learn the complicated syntactical system of any human language. The name is derived from the famous design dictum of German-born U.S. architect Ludwig Mies van der Rohe (1886–1969). [proposed by 21st-century U.S. psychologist Elissa L. Newport]

lethal catatonia

lethal catatonia a form of acute maniacal excitement that in some cases leads to unexplained death. Also called Bell’s mania; deadly catatonia; exhaustion death. See also hypermania. [first described in 1849 by U.S. physician Luther Vose Bell (1806–1862)]

lethal dose (LD)

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lethality

lethality n. the degree of dangerousness or likelihood of death associated with a particular course of action. The word is often used when comparing methods of committing suicide. —lethal adj.

lethality scale

lethality scale a set of criteria used to predict the probability of a suicide or attempted suicide occurring. A variety of such scales exist, most including gender, prior suicide attempts, and psychiatric diagnosis and history.

lethargy

lethargy n. low energy level and lack of motivated behavior, often occurring in depression and a number of other conditions. —lethargic adj.

letter cancellation test

letter cancellation test any of a variety of tests that measure attentional skills, visuomotor abilities, and other functions by requiring the participant to cross out a specific letter repeatedly interspersed among long lines of random letters.

letter-by-letter reading

letter-by-letter reading the process in which individuals identify a word by building up its constituent letters in sequence rather than by recognizing the whole word. It is characteristic of pure alexia.

Letter–Number Sequencing

Letter–Number Sequencing an attentional subtest on more recent versions of the Wechsler Adult Intelligence Scale and the Wechsler Intelligence Scale for Children in which the participant must sequence a random order of numbers and letters. Specifically, the participant must first say the numbers in ascending order and then the letters in alphabetical order. It is generally considered to be a test of verbal working memory.

letting go

letting go discontinuing the struggle for life after a strenuous period of effort and suffering during the dying process. See also acceptance stage.

leuco- (leuc-; leuko-; leuk-)

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leukocyte (leucocyte)

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leukotomy (leucotomy)

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leuprolide

leuprolide n. an analog of gonadotropin-releasing hormone that opposes the action of androgens and estrogens through inhibition of gonadotropin secretion. It is used for the treatment of uterine tumors, some forms of precocious puberty, and advanced prostate cancer. Because of its potent antiandrogen effects, it has been used controversially to perform chemical castration in repeat sex offenders. U.S. trade name (among others): Lupron.

level

level n. in an experimental design, the quantity, magnitude, or category of the independent variable (or variables) being studied. For example, if a researcher is assessing the effect of alcohol on cognition, each specific amount of alcohol included in the study is a level (e.g., 0.0 oz, 0.5 oz, 1.0 oz, 1.5 oz).

Level I–Level II theory

Level I–Level II theory the theory that cognitive abilities can be viewed as being arranged hierarchically at two different levels. The first level is of associative processing (exemplified by rote learning and short-term memory), the second of more conceptual processing (exemplified by categorization, abstraction, and reasoning). [developed by Arthur R. Jensen]

level of analysis

level of analysis the level chosen when examining a multilevel phenomenon, such as the individual (micro-) level, the group or organizational (meso-) level, or the societal (macro-) level.

level of measurement

level of measurement see measurement level.

level of significance

level of significance see significance level.

level-of-aspiration theory

level-of-aspiration theory a conceptual approach to group and individual performance that assumes that one’s initial goals and ambitions influence both particular performances and their emotional, motivational, and behavioral consequences.

levels of consciousness

levels of consciousness 1. varying degrees of alertness, arousal, or vigilance, ranging from the degree experienced in normal wakefulness, to that experienced in unfocused wakefulness, drowsiness, light sleep, or slow-wave (deep) sleep, to that experienced minimally or not at all, as in a minimally conscious state, vegetative state, and coma. Levels of consciousness are defined both behaviorally and by electroencephaolography and other kinds of brain imaging. 2. in certain mystical philosophies, states of pure consciousness that may involve changes in perception, feeling, and thought and that may occur either spontaneously or as a result of practices such as yoga, meditation, breathing techniques, and fasting.

levels of intelligence

levels of intelligence in theories proposing that intelligence can be envisaged as a series of levels, general ability comes at the top of the hierarchy and successively narrower abilities come at lower levels. In one variant, the top level comprises general ability, the second level major group factors, the third level minor group factors, and the fourth level specific factors. Major group factors are those that are measured by many (but not all) intelligence tests, whereas minor group factors are ones that are measured by a smaller number of tests. Specific factors are measured only by single tests.

levels-of-processing model of memory

levels-of-processing model of memory the theory that encoding into memory and therefore subsequent retention depend on the depth of cognitive elaboration that the information receives and that deeper encoding improves memory. In early critical experiments, depth was achieved by processing the meaning of to-be-remembered words rather than focusing on shallower dimensions, such as the sound of the words. [formulated in 1972 by Canadian psychologist Fergus I. M. Craik (1935– ) and Robert S. Lockhart]

Levene test for equality of variance

Levene test for equality of variance a method for evaluating whether the variance in a set of scores is equivalent across two or more groups being studied. Equality of variance is required in analysis of variance and other statistical techniques to obtain valid results. See homogeneity of variance. [Howard Levene (1914–2003), U.S. statistician and geneticist]

lever switch

lever switch a switch mounted on a device at one end with the opposite end free to move within fixed or variable limits. The lever may be any length or shape, requires the use of pressure on the end, and enables individuals with limited fine motor control to operate electrical devices. See also leaf switch.

Levinson’s adult development theory

Levinson’s adult development theory a model of human development in which adulthood is divided into early, middle, and late segments, each period consisting of (a) transitional, or entry, stages (e.g., age-30 transition, age-40 transition), which are often times of uncertainty, self-examination, exploration, and modification of the quality and significance of life commitments, and (b) intervening periods of relative stability, when individuals consolidate new interpretations, structures, and goals and move forward. The adaptations associated with transitional periods may be relatively smooth and uneventful or may be experienced as psychologically difficult and painful (e.g., as a midlife crisis). [proposed by Daniel Levinson (1920–1994), U.S. psychologist]

levitation

levitation n. an allegedly paranormal phenomenon in which a person or thing appears to ascend into the air and hover there without physical cause. Levitation is mainly associated with psychokinesis and poltergeist activity. A sensation of levitating is also common in dreams. —levitate vb.

Levo-Dromoran

Levo-Dromoran n. a trade name for levorphanol.

levodopa (L-dopa)

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levomepromazine

levomepromazine n. see methotrimeprazine.

Levoprome

Levoprome n. a trade name for methotrimeprazine.

levorphanol

levorphanol n. an opioid analgesic produced by manipulation of the morphine molecule. Levorphanol is approximately four to six times more potent as an analgesic than morphine and possesses similar risks of dependence and respiratory depression. U.S. trade name: Levo-Dromoran.

Lewy body dementia

Lewy body dementia a specific type of dementia associated with the presence of abnormal proteins called Lewy bodies in the brain. It is characterized by hallucinations and delusions occurring early in the disease process, marked day-to-day fluctuations in cognition, and spontaneous parkinsonism. [Friedrich Heinrich Lewy (1885–1950), German neurologist]

lexical access

lexical access in psycholinguistics, the process by which an individual produces a specific word from his or her mental lexicon or recognizes it when used by others. See productive vocabulary; receptive vocabulary.

lexical agraphia

lexical agraphia a disorder characterized by an impaired ability to spell irregular words (e.g., yacht) or ambiguous words. The ability to spell other words or nonwords is not affected. Also called surface agraphia.

lexical ambiguity

lexical ambiguity the property of a word that has more than one possible meaning. See ambiguity.

lexical decision

lexical decision a task in which the participant is presented with strings of letters, such as HOUSE or HOUPE, and is required to determine whether each string spells a word. The reaction time required to make the decision is usually measured.

lexical hypothesis

lexical hypothesis the supposition that any significant individual difference, such as a central personality trait, will be encoded into the natural-language lexicon; that is, there will be a term to describe it in any or all of the languages of the world. Also called fundamental lexical hypothesis. [first proposed in 1884 by Francis Galton]

lexical memory

lexical memory see mental lexicon.

lexical word

lexical word see content word.

lexical-selection rules

lexical-selection rules in linguistics, rules governing which lexical items may appear in which sentence structures. For example, intransitive verbs, such as smile or lie, do not allow direct objects and are therefore incompatible with certain syntactic structures. The relationship between lexical selection and sentence structure is of major interest in generative grammar.

lexical–gustatory synesthesia

lexical–gustatory synesthesia see synesthesia.

lexicology

lexicology n. the study of the meanings of words and the relationships between them. Applied lexicology is called lexicography, the science and art of compiling dictionaries.

lexicon

lexicon n. the vocabulary of a language and, in psychology, the lexical knowledge of an individual. See mental lexicon. See also productive vocabulary; receptive vocabulary.

LFA

LFA see low-functioning autism.

LGBTQ

LGBTQ abbreviation for lesbian, gay, bisexual, transgender, and questioning or queer: an inclusive term used to refer to the homosexual population in all of its diverse forms, to those with both homosexual and heterosexual preferences, and to those whose gender identity differs from the culturally determined gender roles for their birth sex.

LGN

LGN abbreviation for lateral geniculate nucleus.

LH

LH 1. abbreviation for lateral hypothalamus. 2. abbreviation for luteinizing hormone.

liability

liability n. 1. in a civil lawsuit, the defendant’s legal responsibility to pay monetary damages for injury or other harm that a court has deemed he or she has caused the plaintiff through, for example, professional malpractice. 2. see multifactorial model.

liberalism

liberalism n. 1. an attitude characterized by acceptance of alternative, even noncompliant, forms of thinking or acting and sometimes (but not necessarily or wholly) by advocacy of change to the status quo and tradition. 2. historically, a broad political philosophy emphasizing individual freedom, constitutional government, and social progress through open debate and the pragmatic reform of existing institutions and laws. —liberal adj.

liberation psychology

liberation psychology a movement that emerged in South America with the intention of making psychology a force in the emancipation of peoples from poverty and injustice rather than a force for maintaining the status quo. The movement was so named by analogy with the liberation theology that arose in Latin American churches in the late 1960s and early 1970s.

libidinal development

libidinal development see psychosexual development.

libidinal stage

libidinal stage in classical psychoanalytic theory, any of the various defined stages of psychosexual development.

libidinal transference

libidinal transference in classical psychoanalysis, the transference of the patient’s libido, or feelings of love, from his or her parents or other loved object onto his or her therapist.

libidinal types

libidinal types in classical psychoanalytic theory, a personality classification based on the distribution of libido, or sexual energy, in the psyche. In the erotic type, the libido remains largely in the id and the main interest is in loving and being loved. In the obsessional type, the libido is largely invested in the superego and the individual is dominated by conscience. In the narcissistic type, the libido is primarily invested in the ego and the main interest is in self-preservation, with little concern for others or for the dictates of the superego. [devised by Sigmund Freud]

libidinization

libidinization n. see erotization.

libido

libido n. 1. in psychoanalytic theory, either the psychic energy of the life instinct in general or the energy of the sexual instinct in particular. In his first formulation, Sigmund Freud conceived of this energy as narrowly sexual, but subsequently he broadened the concept to include all expressions of love, pleasure, and self-preservation. See also Eros. 2. in the analytic psychology of Carl Jung, the general life force that provides energy for all types of activities: biological, sexual, social, cultural, and creative. 3. more generally, sexual energy or desire. —libidinal adj. —libidinize vb. —libidinous adj.

libido-binding activity

libido-binding activity an activity in which members of a therapy group concentrate libidinal energies on a specific interest or occupation rather than on activities that stimulate the libido. [introduced by Russian-born U.S. psychotherapist Samuel Richard Slavson (1890–1981)]

Librium

Librium n. a trade name for chlordiazepoxide.

license

license n. permission granted by a government agency for an individual or organization to engage in a given occupation or business on the basis of examination, proof of education, or both rather than on measures of performance. See professional licensing. —licensed adj. —licensure n.

licensed practical nurse (LPN)

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licking behavior

licking behavior the licking by an animal of itself or another animal, particularly an offspring. Licking behavior appears to be part of the maternal behavior of many mammals; the pregnant female licks itself before giving birth, then licks the offspring, thereby establishing a means of identifying its own young. Licking of the offspring’s urine may serve to maintain the female in fluid homeostasis during lactation.

lickometer

lickometer n. see drinkometer.

lid apraxia

lid apraxia see oculomotor apraxia.

lie

lie n. a false statement or a false presentation, known to be untrue, that is made with the intention to deceive. Despite the moral and legal proscription against lies, they are a cognitive signal that the liar understands enough of what others are thinking to be motivated to lie to them. In children, acquiring an understanding of this sort represents a cognitive milestone usually reached around age 3 (see theory of mind). At that age, a child’s initial lies tend to be indiscriminate; he or she is not yet aware of the moral qualms associated with them. By age 4, children can reliably tell the difference between harmful lies and white lies, and they stop lying indiscriminately. As they grow older, their lying becomes more sophisticated (i.e., plausible), a social skill that is influenced by their particular culture, which plays a pivotal role in determining how they lie and when they feel it is appropriate to lie. See also fabrication; pathological lying. Compare confabulation; fabulation. —liar n. —lie, lying vb.

lie detector

lie detector see polygraph.

lie scale

lie scale a set of items within a psychological instrument (particularly a personality assessment) used to indicate whether a respondent has been truthful in answering. For example, an honest participant would respond similarly to the items “I never regret the life decisions I have made” and “I’ve never done anything I later wished I could take back,” which are different ways of presenting the same concept. Conversely, a respondent trying to present himself or herself as positively as possible might answer such related questions inconsistently.

Liebmann effect

Liebmann effect the perceived merger of different visual stimuli that occurs when the border between them is defined only by hue. [Susanne E. Liebmann (1897–1990), German psychologist]

life coaching

life coaching a form of teaching and encouragement (one-to-one or coach-to-group) designed to help individuals identify and meet goals of importance to them in their personal and work lives.

life crisis

life crisis a period of distress and major adjustment associated with a significant life experience, such as divorce or death of a family member. In studies relating health to life crises, individuals experiencing recent major stress-producing experiences are more likely than others to show significant alterations in mental and physical health status.

life cycle

life cycle 1. the sequence of developmental stages through which an organism passes between a specified stage of one generation (e.g., fertilization, birth) and the same stage in the next generation. 2. the series of stages that characterizes the lifespan of a group, institution, culture, or product.

life events

life events important occasions throughout the lifespan that are either age-related and thus expected (e.g., marriage, retirement) or unrelated to age and unexpected (e.g., accidents, relocation). Contextual theories of personality often assume that personality is shaped by reactions to stress produced by critical life events. See also off-time life events; on-time life events.

Life Events Rating Scale

Life Events Rating Scale an instrument used to measure the relative impact of diverse stress-producing life experiences, changes, and crises. The derived score is expressed in life-change units. The scale is more formally known as the Social Readjustment Rating Scale. [developed in 1967 by U.S. psychiatrists Thomas H. Holmes and Richard H. Rahe]

life expectancy

life expectancy the number of years that a person can, on average, expect to live. Life expectancy is based on statistical probabilities and increases with improvements in medical care and hygiene.

life force

life force see élan vital.

life goal

life goal in the individual psychology of Alfred Adler, the individual’s concept of what he or she could attain in life, seen as a means of compensating for real or imagined inferiority. See also life plan.

life history

life history in therapy and counseling, a systematic account of the client’s development from birth to the present, including the meaningful aspects of the client’s emotional, social, and intellectual development. The account is taken by the therapist or counselor directly from the client and may additionally be derived from autobiographical material.

life instinct

life instinct in psychoanalytic theory, the drive comprising the self-preservation instinct, which is aimed at individual survival, and the sexual instinct, which is aimed at the survival of the species. In the dual instinct theory of Sigmund Freud, the life instinct, or Eros, stands opposed to the death instinct, or Thanatos. Also called erotic instinct.

life lie

life lie 1. the false conviction held by some individuals that their life plan is bound to fail due to other people or to circumstances beyond their control. This was postulated as a method of freeing oneself from personal responsibility. [defined by Alfred Adler] 2. any false belief around which an individual’s life is built.

life plan

life plan in the individual psychology of Alfred Adler, an individual’s style of life and guiding fiction as he or she strives to reach his or her life goal.

life review

life review the process whereby individuals, especially older adults, reflect upon and analyze past life experiences. Life review, or analytical reminiscence, is often made use of in counseling older adults with symptoms of mild depression or people of any age with terminal illness, sometimes as an adjunct to psychotherapy. [defined in 1961 by U.S. gerontologist and psychiatrist Robert N. Butler (1927–2010)]

life rhythm

life rhythm see biological rhythm.

life satisfaction

life satisfaction the extent to which a person finds life rich, meaningful, full, or of high quality. Numerous standardized measures have been developed to provide an index of a person’s life satisfaction in comparison to various normative groups (e.g., Satisfaction With Life Scale). Improved life satisfaction is often a goal of treatment, especially with older people. See also quality of life.

life space

life space in the field theory of Kurt Lewin, the “totality of possible events” for one person at a particular time; a person’s possible options together with the environment that contains them. The life space is a representation of the environmental, biological, social, and psychological influences that define one person’s unique reality at a given moment in time. Contained within the life space are positive and negative valences, that is, forces or pressures on the individual to approach a goal or move away from a perceived danger.

life stress

life stress severe strain produced by critical life events or similar experiences, such as failure at work, marital separation, or loss of a loved one.

life-change unit (LCU)

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life-history method

life-history method a structured interview that attempts to summarize historical data about events that are relevant to evaluating a person’s current functioning.

life-space interview

life-space interview a form of crisis intervention in which children in day and residential treatment are interviewed by staff members during moments of crisis or stress, for example, immediately after receiving an upsetting letter or after being attacked by another child. Efforts are made to convert these events into therapeutic experiences by such means as restoring the children’s belief in themselves and strengthening their ego. [originated by Austrian-born U.S. psychologist Fritz Redl (1902–1988)]

lifeline

lifeline n. a therapeutic technique used in group or individual therapy in which each individual draws lines representing his or her life, marking past and future expected events with angles indicating even, upward, or downward progression of functioning, as well as specific dates and the affect surrounding these events. Discussion of this diagram with the therapist can enhance awareness and understanding of the individual’s life patterns.

lifespan

lifespan n. 1. the maximum age that can be obtained by any given individual within a particular species. 2. the precise length of an individual’s life.

lifespan contextualism

lifespan contextualism a perspective on human development that views people as both products and producers of their own development, interacting throughout life with family, peers, and other social groups and institutions.

lifespan developmental psychology

lifespan developmental psychology the study of psychological and behavioral change across and within individuals from birth through death using a lifespan perspective. Such an approach assumes that human developmental processes are complex, interactive, and fully understood only in the context of influencing events. It also assumes that there is no end state of maturity and that not all developmental change is related to chronological age.

lifespan perspective

lifespan perspective a general perspective emphasizing (a) that human development is a lifelong process of change from conception to death; (b) that developmental change is multidimensional and multidirectional, involving both growth and decline in one’s performance (e.g., of cognitive tasks); and (c) that there is plasticity in human behavior throughout the entire lifespan.

lifestyle

lifestyle n. 1. the typical way of life or manner of living that is characteristic of an individual or group, as expressed by behaviors, attitudes, interests, and other factors. 2. in the individual psychology of Alfred Adler, an individual’s characteristic way of overcoming or compensating for feelings of inadequacy. According to Adler, a lifestyle is first adopted in childhood, when the key factors informing it will be genetic endowment, upbringing, and interpersonal relations within the family.

Lifetime of Experiences Questionnaire (LEQ)

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lifetime personality

lifetime personality the pattern of behavior that dominates a person’s life between birth and death. [from the personality theory of Henry Alexander Murray]

lifetime risk

lifetime risk the odds that one will be diagnosed with a disease or condition during one’s lifetime (usually stated in terms of 70 to 85 years). It is often important for individuals undergoing genetic counseling to differentiate lifetime risk from the risk of being diagnosed with the disease in the next 5 or 10 years.

ligand

ligand n. a molecule that binds to a specific site on another molecule, for example, a hormone binding to its receptor molecule at the surface of a cell.

ligand-gated ion channel

ligand-gated ion channel an ion channel that opens or closes in response to the binding of a molecule (the ligand) to a receptor. An example is the ionotropic receptor. Compare voltage-gated ion channel.

light adaptation

light adaptation the process by which the eye adjusts to conditions of high illumination, as occurs when a person exits a dark theater into a sunny parking lot. It takes less than 10 minutes and involves constriction of the pupil and a shift in the sensitivity of the retina so that the retinal cones become active in place of the retinal rods. Compare dark adaptation.

light cell

light cell see Type II cell.

light induction

light induction the production or alteration of sensation in one part of the visual field by stimulation in an adjacent part of the field (e.g., induced color).

light pointer

light pointer a form of headstick fitted with a light that can activate an assistive technology device.

light reflex

light reflex see pupillary reflex.

light sensitivity

light sensitivity see photophobia.

light therapy

light therapy see phototherapy.

light trance

light trance see trance.

light–dark cycle

light–dark cycle the schedule according to which the lights are turned on and off in rooms housing research animals. A 12-hour light–dark cycle, in which the lights are on for 12 consecutive hours and then off for 12 consecutive hours, is commonly used.

lightness constancy

lightness constancy see brightness constancy.

lightness contrast

lightness contrast see brightness contrast.

lightning calculator

lightning calculator an individual capable of extremely rapid mental calculations. Although some of these individuals have a high IQ, most of them are people with a very well developed specific ability but not a particularly high IQ.

likelihood

likelihood n. in statistics, the probability of obtaining a particular set of results given a set of assumptions about the distribution of the phenomena in the population and the parameters of that distribution.

likelihood function

likelihood function a formula that yields the probability of obtaining a particular distribution of values in a sample for each known value of an associated population parameter. In other words, it indicates how likely a particular population is to produce the observed sample data under certain conditions.

likelihood principle

likelihood principle 1. the generality originally proposed in 1867 by Hermann von Helmholtz that an observer will tend to perceive the most likely interpretation of a visual stimulus (i.e., the one with the highest probability of being correct). This is in contrast to the simplicity principle, elaborated in 1953 by U.S. psychologist Julian E. Hochberg (1923– ) with Edward McAlister, which states that an observer will tend to perceive the simplest interpretation (i.e., the one with the shortest description). 2. a foundational tenet of statistical inference stating that where there is an unknown population parameter, θ, and an observed sample distribution, x, all relevant information about the population distribution is contained in the likelihood function for x.

likelihood ratio (LR)

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Likert scale

Likert scale a type of direct attitude measure that consists of statements reflecting strong positive or negative evaluations of an object. Five-point scales are common and a neutral middle point may or may not be included. For example, an assessment item using a Likert scale response format (i.e., a Likert-type question or Likert-type item) might include the following statement choices: strongly disagree, disagree, neither disagree nor agree, agree, and strongly agree. The respondent chooses the option most representative of his or her view (e.g., on whether same-sex marriages should be permitted) and these ratings are summed to provide a total attitude score for a topic of interest. Also called Likert summated rating procedure. [Rensis Likert (1903–1981), U.S. psychologist]

liking scale

liking scale a measure of a person’s degree of attraction to another individual, usually involving a willingness to be in the other’s company as well as a positive evaluation of the other’s personality characteristics. One such scale was published by U.S. social psychologist Zick Rubin (1944– ) in 1970. Although Rubin distinguished between this measure and his love scale, studies have shown that the two indices are usually positively correlated.

Lilliputian hallucination

Lilliputian hallucination a visual hallucination of objects, animals, or people greatly reduced in size, which may result from a number of conditions, such as delirium tremens, typhoid, or brain tumors in the temporal lobe. The name is derived from Jonathan Swift’s Gulliver’s Travels (1726), in which Gulliver journeys to the imaginary land of Lilliput, populated by tiny people. Also called diminutive visual hallucination; microptic hallucination. See also micropsia.

limb kinetic apraxia

limb kinetic apraxia see apraxia.

limbic cortex

limbic cortex the portions of the cerebral cortex, especially the cingulate cortex, that are associated with the limbic system.

limbic epilepsy

limbic epilepsy a type of neurological disorder in which recurrent seizures spontaneously arise in areas of the limbic system. Recent research suggests that altered connectivities between hippocampal granule cells and pyramidal cells—as mediated by neurotrophins and their receptors—play a crucial role in the development of limbic epilepsy by potentially changing the balance of excitation and inhibition in the hippocampus and amygdala, which are essential to memory and emotion. Acetylcholine and other amino acid neurotransmitters have also been implicated in the etiology of limbic epilepsy, as have early life stressors, such as maternal separation. Additionally, febrile seizures may contribute to the generation of subsequent limbic epilepsy by increasing hippocampal excitability. Also called medial temporal lobe epilepsy; mesial temporal lobe epilepsy.

limbic lobe

limbic lobe a fifth subdivision of each cerebral hemisphere that is often distinguished in addition to the four main lobes (see cerebrum). It comprises the cingulate cortex, parahippocampal gyrus, and hippocampal formation.

limbic system

limbic system a loosely defined, widespread group of brain nuclei that innervate each other to form a network that is involved in autonomic and visceral processes and mechanisms of emotion, memory, and learning. It includes portions of the cerebral cortex (see limbic lobe), thalamus, and certain cortical and subcortical structures, such as the hippocampus, amygdala, and septal area.

Limbitrol

Limbitrol n. a trade name for a combination of the tricyclic antidepressant amitriptyline and the benzodiazepine chlordiazepoxide, appropriate for the treatment of concurrent anxiety and depression but not now commonly used.

limen

limen n. see threshold.

limerence

limerence n. an intense sexual desire and a strong concern for the other person in a romantic relationship, accompanied by great sensitivity to how that other person is reacting to oneself. Limerence typically diminishes in intensity a month or two after the relationship is formed. See also passionate love; romantic love. [first described in 1979 by U.S. psychologist Dorothy Tennov (1928–2007)]

liminal

liminal adj. relating to the threshold of a sensation.

limited competency

limited competency a determination by a court that a person has the capacity to manage some but not all of his or her activities. A limited guardian is appointed to assist the individual in exercising certain legal rights, such as the right to enter into contracts, get married, provide consent (e.g., for medical treatment), or vote.

limited guardianship

limited guardianship a form of legal guardianship of a child or adult with a disability (e.g., intellectual disability) in which a guardian has authority with respect to some areas of activity (e.g., legal, financial, health-related) in which the ward is not capable. In some jurisdictions, the term is used interchangeably with conservatorship.

limited hold

limited hold a feature that can be added to a schedule of reinforcement in which the opportunity for reinforcement is limited to a fixed period. For example, if a fixed-interval schedule in which reinforcement is given after 1 minute had a 2-second limited hold, then only responses occurring within 2 seconds of the end of the 1-minute interval would be reinforced.

limited responsibility

limited responsibility see diminished responsibility.

limited-capacity system

limited-capacity system a conceptualization of working memory in which resource constraints restrict the processing of information. When new information is encountered, older information is either relegated to long-term memory or eliminated, providing the resources to retain the newer data. Attention and consciousness are often similarly conceived of as limited-capacity systems. See also chunking.

limophthisis

limophthisis n. the physical and mental signs of emaciation caused by severe undernourishment.

Limulidae

Limulidae n. see horseshoe crab.

line graph

line graph a graph in which data points representing a series of individual measurements are shown connected by straight line segments. Line graphs often are used to show trends over time, such as population growth. Also called line chart.

line management

line management a system of management in which individuals have authority over those immediately below them in the chain of command and are accountable to those immediately above. See unity of command.

line of beauty

line of beauty an S-shaped curve said by the British painter William Hogarth (1697–1764) to possess maximal beauty.

line of fixation

line of fixation a straight line between the object of visual focus and the fovea centralis.

line of regard

line of regard a straight line between an object being viewed and the center of rotation of the eye.

line spectrum

line spectrum see sound spectrum.

linear

linear adj. describing any relationship between two variables (x and y) that can be expressed in the form y = a + bx, where a and b are numerical constants. No coefficient can be raised to a power greater than 1 or be the denominator of a fraction. When depicted graphically, the relationship is a straight line. Compare nonlinear.

linear causation

linear causation the simplest type of causal relationship between events, usually involving a single cause that produces a single effect or a straightforward causal chain. Linear causation is often contrasted with more complex models of causation involving multiple causes and effects (see causal ambiguity; causal texture), feedback loops, and indirect or remote causes.

linear correlation

linear correlation a measure of the degree of association between two variables that are assumed to have a linear relationship, that is, to be related in such a manner that their values form a straight line when plotted on a graph. It provides an index of the degree of constant change in the value of one variable (y) for each unit change in the value of another variable (x).

linear model

linear model any model for empirical data that attempts to relate the values of an outcome or dependent variable to the explanatory or independent variables through a linear function, this is, one that simply sums terms and includes no exponents greater than 1. Most commonly used statistical techniques (analysis of variance, regression analysis, etc.) can be represented as linear models. Compare nonlinear model.

linear perspective

linear perspective one of the monocular depth cues, arising from the principle that the size of an object’s visual image is a function of its distance from the eye. Thus, two objects appear closer together as the distance from them increases, as seen in the tracks of a railroad that appear to converge on the horizon.

linear program

linear program a form of programmed instruction in which the learner independently studies information presented (e.g., via a booklet) in small, discrete, step-by-step frames that usually become progressively more complex. Correct answers to review questions are given after each frame so as to provide immediate feedback and continuous reinforcement.

linear regression

linear regression a regression analysis in which the predictor or independent variables (xs) are assumed to be related to the criterion or dependent variable (y) in such a manner that increases in an x variable result in consistent increases in the y variable. In other words, the direction and rate of change of one variable is constant with respect to changes in the other variable. The analysis yields a regression equation that includes an intercept and regression coefficients for the predictors. Compare nonlinear regression.

linear relationship

linear relationship an association between two variables that when subjected to regression analysis and plotted on a graph forms a straight line. In linear relationships, the direction and rate of change in one variable are constant with respect to changes in the other variable. Compare nonlinear relationship.

linear system

linear system a system in which the response to a complex input is the sum of the responses to the separate components of the input (this is the principle of superposition). In addition, another condition (homogeneity) is necessary: If an input is increased by a certain factor, the output must increase by the same factor.

linear transformation

linear transformation the transformation of a set of raw data using an equation that involves addition, subtraction, multiplication, or division with a constant. An example is the transformation of x to y by means of the equation y = a + bx, where a and b are numerical constants. A plot of such transformed data would form a straight line. Data are often subjected to linearizing to determine whether a linear model provides a better fitting or more parsimonious explanation of the variables. Compare nonlinear transformation.

linear type

linear type a body type characterized by a slender, narrow-chested, long-necked, long-nosed physique, sometimes equated with the asthenic type in Kretschmer typology.

linearizing

linearizing n. see linear transformation.

lineup

lineup n. an identification procedure in which several individuals are presented to an eyewitness of a crime at the same time or in a sequence. The witness is asked to indicate if he or she recognizes one of the lineup members as the perpetrator of the crime.

lingering trajectory

lingering trajectory see trajectories of dying.

lingua franca

lingua franca a common language used by people of different mother tongues for purposes of communication. Such a language may, but need not, be a hybrid of the mother tongues. Compare creole; pidgin.

lingual

lingual adj. of or relating to the tongue or to speech and languages.

lingual frenulum

lingual frenulum see frenulum.

lingual gland

lingual gland any of the glands on the surface of the tongue whose seromucous secretions are thought to circulate tastants among the taste cells.

lingual gyrus

lingual gyrus a relatively short convolution of the inferior (lower) brain surface extending from the occipital to temporal lobes and that is medial to the fusiform gyrus. It is important in recognizing faces and landmarks and has been implicated in the generation and recall of dreams.

lingual nerve

lingual nerve a branch of the trigeminal nerve that supplies fibers to the mucous membranes of the mouth and the anterior (front) two thirds of the tongue, including the taste-bud papillae. Also called gustatory nerve.

lingual papilla

lingual papilla see papilla.

linguist

linguist n. a scholar who specializes in the study of linguistics or any of its branches. A linguist may focus on the characteristics of a specific language or group of languages or on certain features of human language in general. He or she will not necessarily have a command of multiple languages, the more precise term for such a person being a polyglot.

linguistic approach

linguistic approach a method of reading instruction that applies what the child already knows about language from having learned to speak it. Letters and sound equivalents are taught by being embedded in meaningful words with regular spelling patterns to maximize the similarities between the familiar spoken language and the unfamiliar written language.

linguistic awareness

linguistic awareness see metalinguistic awareness.

linguistic determinism

linguistic determinism the hypothesis, most commonly associated with the U.S. linguists Edward Sapir (1884–1939) and Benjamin Lee Whorf (1897–1941), that the semantic structure of a particular language determines the structure of mental categories among its speakers. Because languages differ in how they refer to basic categories and dimensions, such as time, space, and duration, native speakers of these languages are assumed to show corresponding differences in their ways of thinking. Also called Sapir–Whorf hypothesis; Whorfian hypothesis. Compare linguistic relativity. See also anthropological linguistics; contrastive rhetoric.

linguistic intergroup bias

linguistic intergroup bias the tendency to describe and evaluate positive behaviors by ingroup members and negative behaviors by outgroup members more abstractly than negative ingroup and positive outgroup behaviors. See also ingroup bias.

linguistic minority

linguistic minority the group of individuals in a polity who are native speakers of a minority language.

linguistic relativity

linguistic relativity the observation that languages differ in the ways in which semantic space is identified and categorized. For example, the Native American language Hopi uses one word for water in a natural setting and another word for water in a vessel but has only one word for flying objects, which is applied to birds, insects, airplanes, and the like. Linguistic relativity is not to be equated with linguistic determinism, which is a theoretical commitment to the idea that these differences have cognitive consequences. See anthropological linguistics.

linguistic typology

linguistic typology the classification of languages with respect to their structural characteristics rather than their historical relationships (genetic linguistics) or geographical distribution (areal linguistics).

linguistic universal

linguistic universal see language universal.

linguistic–kinesic method

linguistic–kinesic method the objective study of disordered behavior in terms of language and movement involved in interactions between individuals.

linguistics

linguistics n. the scientific study of the physical, structural, functional, psychological, and social characteristics of human language. See also psycholinguistics; sociolinguistics.

link analysis

link analysis in ergonomics, the analysis of operational sequences and the movements of workers or objects that these entail to determine the design of tools, equipment, jobs, and facilities that will best serve worker efficiency and safety.

linking verb

linking verb see copula.

Lioresal

Lioresal n. a trade name for baclofen.

liothyronine

liothyronine n. a pharmaceutical preparation of L-triiodothyronine, a naturally occurring thyroid hormone, used to treat conditions associated with thyroid deficiency. It is also used as an adjunct to standard antidepressant therapy in the management of depression that has not responded to standard therapy alone. U.S. trade name (among others): Cytomel.

lip biting

lip biting habitual biting of the lips, which may be a nervous habit, a stereotyped behavior (see stereotypy), or a symptom of a disorder, such as Lesch–Nyhan syndrome. Also called morsicatio labiorum.

lip eroticism

lip eroticism the use of the lips to obtain sexual arousal or satisfaction.

lip pursing

lip pursing a facial contortion in which the lips protrude in a manner that resembles pouting or a snout. First described (as Schnauzkrampf) by German psychiatrist Karl Ludwig Kahlbaum (1828–1899), it is most commonly associated with catatonic schizophrenia.

lipid-metabolism disorders

lipid-metabolism disorders a group of metabolic anomalies characterized by abnormal levels of fatty substances in the blood or other tissues resulting from genetic, endocrine, or external factors or organ failure. Lipid-metabolism disorders include Niemann–Pick disease and Tay–Sachs disease.

lipodystrophy

lipodystrophy n. any disorder of lipid metabolism. Kinds of lipodystrophy include intestinal lipodystrophy, in which a malabsorption of fats from the digestive tract may be associated with lesions in the central nervous system (as in Whipple’s disease), and progressive lipodystrophy, marked by a symmetrical loss of subcutaneous fat deposits and abnormal deposits of fat around the kidney, heart, and abdominal cavity. No consistent neurological abnormalities are associated with the latter form of lipodystrophy, but nearly 20% of the patients in one study showed signs of intellectual disability. The cause of progressive lipodystrophy is unknown. Lipodystrophy is also associated with diabetes mellitus in a form marked by loss of subcutaneous fat in areas injected with insulin; this is known as lipotrophic diabetes mellitus or insulin lipodystrophy. Manifestations of lipodystrophy are also often found in people with HIV. See also partial lipodystrophy; total lipodystrophy.

lipostatic hypothesis

lipostatic hypothesis a hypothesis stating that the long-term regulation of food intake is governed by the concentration in the blood of free fatty acids, which result from the metabolism of fat. High concentrations indicate the breakdown of fat, and food consumption increases accordingly; low concentrations are associated with reduction in consumption. Also called lipostatic theory. See also glucostatic theory. [originally proposed in 1953 by Gordon C. Kennedy]

lipotrophic diabetes mellitus

lipotrophic diabetes mellitus see lipodystrophy.

Lipps illusion theory

Lipps illusion theory a theory that explains the perception of a variety of visual illusions as visual distortions induced by the emotional state of the observer. [Theodor Lipps (1851–1914), German philosopher and psychologist]

lipreading

lipreading n. a method used by some people with hearing loss to understand spoken words in which the listener interprets the speaker’s lip movements. Some authorities claim that only about one third of speech sounds can be accurately read in this way and that attention to facial expression and general body language, with the additional use of sign language, assist significantly in comprehension. Also called speechreading.

liquid

liquid 1. adj. in phonetics, denoting a frictionless speech sound produced when the soft palate is raised and the airstream is only partially obstructed, such as [l] or [r]. 2. n. a liquid speech sound.

liquidation of attachment

liquidation of attachment the process of freeing a patient from a painful situation by unraveling the attachments by which he or she is bound. [defined by Pierre Janet]

lisdexamfetamine

lisdexamfetamine n. a prodrug of dextroamphetamine used in the treatment of attention-deficit/hyperactivity disorder. Potentially serious side effects include slowed growth in children, cardiovascular risks (e.g., myocardial infarction, hypertension), and psychotic or manic symptoms. U.S. trade name: Vyvanse.

lisp

lisp 1. n. incorrect production of sibilant sounds caused by faulty tongue placement or abnormalities of the articulatory mechanism. Speech and language pathologists have described various types of lisps, including four primary forms: the interdental (or frontal) lisp, in which the tongue protrudes between the front teeth and airflow is directed forward and only partially obstructed; the dental lisp, in which the airflow is partially impeded by contact with the tongue as it rests on or pushes against the front teeth or alveolar ridge; the lateral lisp, in which airflow and saliva are pushed forward over the sides of the broadly extended tongue, creating a wet sound; and the palatal lisp, in which the airflow is partially disrupted by the middle area of the tongue touching the rear portion of the soft palate. See also sigmatism. 2. vb. to speak using a lisp. —lisping n. LISP n. LIS(t) P(rocessing): the second oldest high-level computer programming language still in use. It was the primary language for writing artificial intelligence programs from the 1960s through the 1980s. The list is the primary data structure, and the basic unit of the language, the s-expression (symbolic expression), is defined recursively (i.e., if X is an s-expression, then so is the list of X). [created by U.S. computer scientist John McCarthy (1927–2011)]

LISP

lissencephaly

lissencephaly n. severe malformation of the convolutions (gyri) in the cerebral cortex due to abnormal neuronal migration during development. It is an umbrella term encompassing several conditions: agyria, the complete absence of convolutions; pachygyria (or macrogyria), unusually thick convolutions; and polymicrogyria (or micropolygyria), unusually small but numerous convolutions. Lissencephaly results in severe developmental delay, severe to profound intellectual disability, motor impairment, and epilepsy.

listening

listening n. an essential activity in therapy and counseling that involves attending to the words and actions of the client as well as to the intentions conveyed by the words. See also active listening.

listening attitude

listening attitude 1. in a therapeutic setting, a therapist’s openness to a client’s personal experience, or a client’s openness to his or her own personal experience. 2. a behavior set in which a person expects and prepares to receive a message. Italian-born U.S. psychiatrist Silvano Arieti (1914–1982) claimed that a person with schizophrenia who is habitually prepared to experience a hallucination may learn to avoid it when made aware of this attitude.

listening strategy

listening strategy the tendency for listeners to pay more attention at the beginning and end of a talk than in the middle.

listwise deletion

listwise deletion a strategy for dealing with the problem of missing data in which an entire case record is excluded from statistical analysis if values are found to be missing for any variable of interest. For example, consider a researcher examining the relationships among grade point averages in high school, scores on college admissions tests, and grade point averages in college. If, for whatever reason, a value has not been recorded for one of those variables for certain participants, all of the information for those individuals is removed from the data set and analyses are performed only on the remaining (complete) records. Also called casewise deletion; complete-case analysis. Compare pairwise deletion.

literacy

literacy n. 1. the ability to read and write in a language. See also biliteracy. 2. the quality of being educated as well as knowledgeable. 3. the quality of having a clear understanding of traditional and contemporary literature. —literate adj.

literacy test

literacy test any test that examines the ability to read and write or an individual’s understanding of literature.

literal alexia

literal alexia a form of alexia in which a person cannot recognize individual letters or numerals and confuses such letters as d and b. Also called literal dyslexia.

literal paraphasia

literal paraphasia a type of speech disturbance in which phonemes are substituted, exchanged, deleted, or added in speech, making it difficult to comprehend what the individual is trying to say. For example, tar may be used for car. Also called phonological paraphasia. See paraphasia.

literal replication

literal replication see replication.

literalism

literalism n. 1. adherence to observable facts, as exhibited in Jean Piaget’s construct of objective responsibility. 2. verbal or nonverbal answers of “yes” or “no,” without cognitive elaboration, to questions during hypnosis, asserted by some but strongly refuted by others to be a marker of hypnotic trance. 3. adherence to the explicit meaning of a text or doctrine, as in biblical literalism.

lithium

lithium n. an element of the alkali metal group whose salts are used in psychopharmacotherapy as mood stabilizers. Lithium salts were first used for the treatment of mania in the 1940s, but widespread use was limited by their toxicity. However, after further investigations into their role in treating bipolar depression and better appreciation of the appropriate dosage, lithium salts entered broader clinical practice in the 1970s. Although its primary indication is in managing bipolar disorder, lithium has some efficacy in managing acute manic phases and in reducing relapse. Its mechanism of action remains unclear; it may work via inhibition of the recycling of inositol from the inositol phosphates, which are second messengers in cellular signaling. Toxic doses are no more than two to three times the therapeutic dose, and serum monitoring is required. Symptoms of acute toxicity include tremors, diarrhea, vomiting, and incoordination; at higher doses, disturbances of heart rhythm and neurological function leading to coma and death may occur. Long-term lithium use can cause thyroid and renal dysfunction in a small percentage of patients. Lithium has been associated with fetal cardiac malformation (Ebstein’s anomaly), and its use during pregnancy is not recommended. U.S. trade names (among others): Eskalith; Lithobid.

litigious paranoia

litigious paranoia a type of paranoid disorder characterized by constant quarreling, claims of persecution, and insistence that one’s rights have been breached. The individual usually threatens to go to court—and frequently does so—to seek redress for exaggerated or imagined wrongs. Also called paranoia querulans; paranoid litigious state.

Little Albert

Little Albert the name of a boy used by John B. Watson and his graduate student Rosalie Rayner (1899–1935) to demonstrate classical (or Pavlovian) fear conditioning in humans.

Little Hans

Little Hans a landmark case of Sigmund Freud’s, illustrating the Oedipus complex. Freud traced a child’s phobia for horses to castration anxiety stemming from masturbation, to repressed death wishes toward the father, and to fear of retaliation owing to rivalry with the mother, with displacement of these emotions onto horses. Freud never actually met the boy but analyzed him through written communication with the father. The case was reported in “Analysis of a Phobia in a Five-Year-Old Boy” (1909).

living will

living will see advance directive.

LLD

LLD abbreviation for language learning disability. See specific language impairment.

Lloyd Morgan’s canon

Lloyd Morgan’s canon the principle that the behavior of a nonhuman animal should not be interpreted in complex psychological terms if it can instead be interpreted with simpler concepts. Lloyd Morgan’s canon, proposed in 1894, helped eliminate the older concept of anthropomorphism, or the endowment of animals with human traits, although some recent authors have argued that its application oversimplifies the abilities of animals. Also called Morgan’s canon; Morgan’s principle. [Conwy Lloyd Morgan]

LLR

LLR abbreviation for log-likelihood ratio.

LMX theory

LMX theory abbreviation for leader–member exchange theory.

LNNB

LNNB abbreviation for Luria–Nebraska Neuropsychological Battery.

lobe

lobe n. a subdivision of an organ, such as the brain or the lungs, particularly when rounded and surrounded by distinct structural boundaries, such as fissures. The four main lobes of each cerebral hemisphere of the brain are the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. There are also subdivisions of each of these lobes; for example, the temporal lobe comprises the inferior, middle, and superior temporal lobes. —lobar adj. —lobate adj.

lobectomy

lobectomy n. complete or partial surgical removal of a lobe, particularly in the brain. The most frequently performed lobectomy is done for seizure control and involves the anterior temporal lobe (see temporal lobectomy).

lobotomy

lobotomy n. incision into various nerve tracts in the frontal lobe of the brain. The original surgical procedure, called prefrontal (or frontal) lobotomy, was introduced in 1936 by Portuguese neurologist Antonio Egas Moniz (1874–1955): Connections between the frontal lobe and other brain structures—notably the thalamus—were severed by manipulating a narrow blade known as a leukotome inserted into brain tissue through several small holes drilled in the skull. A second procedure, called transorbital lobotomy, was devised in 1945 and involved the manipulation of a pointed instrument resembling an ice pick driven with a mallet through the thin bony wall of the eye socket and into the prefrontal brain. Both procedures were widely used to relieve the symptoms of severe mental disorder (including depression and schizophrenia) until the advent of antipsychotic drugs in the 1950s. These operations did, on occasion, result in improved function for some patients, but others either died as a consequence of the surgery or suffered major personality changes, becoming apathetic and prone to inappropriate social behavior; some also developed a seizure disorder. Such procedures have since been replaced by more sophisticated, stereotactic forms of neurosurgery that are less invasive and whose effects are more certain and less damaging. Also called leukotomy.

LOC

LOC abbreviation for loss of consciousness.

local circuit

local circuit see neural circuit.

local circuit neuron

local circuit neuron a neuron with short processes that do not extend far from the cell body. Also called Golgi Type II neuron. Compare projection neuron.

local enhancement

local enhancement a form of social learning in which one or more individuals engaging in some behavior with an object in a particular location draw the attention of another to that location, which facilitates the acquisition of similar behavior by that observer. The attraction of attention to a particular place in the environment, not any specific social interactions among the demonstrators and observer, is what leads to learning. For example, ducks in a pen may ignore an escape hole unless they are near another duck who escapes through the hole, thus drawing their attention to it.

local excitatory state (LES)

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local independence

local independence in factor analysis and other models involving latent variables, the basic assumption that individual observations have no direct influence on one another and that any relationship between them is to be explained by the latent variable underlying them.

local potential

local potential the phase of a graded potential that precedes the action potential if the localized stimulation is above threshold level. Also called local response.

local regression (loess; lowess)

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local–global distinction

local–global distinction the difference between perceiving a whole form and perceiving the subunits that make up that form. For example, if a large letter S is formed from an arrangement of small letter ps, perception is at the local level if it focuses on the ps and at the global level if it focuses on the S.

localization

localization n. the ability to determine the physical position or spatial location of a stimulus in any sensory modality.

localization of function

localization of function the concept that specific parts of the cerebral cortex are relatively specialized for particular types of cognitive and behavioral processes. Also called cortical localization.

localized amnesia

localized amnesia a memory loss restricted to specific or isolated experiences. Also called circumscribed amnesia; lacunar amnesia.

location constancy

location constancy the tendency for a resting object and its setting to appear to have the same position even if the relationship between setting and observer is altered as the observer shifts position. See also object constancy.

location-invariant neuron

location-invariant neuron any of various neurons located in extrastriate visual areas, particularly those in the inferotemporal cortex, that respond regardless of the location of a stimulus in the receptive field. Because the receptive fields in these areas are so large, a stimulus may be located almost anywhere in the visual field. Many of these cells are also size-invariant neurons, which respond when presented with a particular object, regardless of its size.

loci

loci pl. n. see locus.

loci method

loci method see method of loci.

lock-and-key theory

lock-and-key theory 1. generally, any theory that posits a specific fit between two or more of its components, in a manner analogous to the fit of a key in a lock. 2. in olfaction, see stereochemical smell theory.

Locke’s theory of goal setting

Locke’s theory of goal setting a theory suggesting that (a) specific goals direct activity more effectively than do vague or general goals, (b) difficult or challenging goals produce better performance than do moderate or easy goals, and (c) short-term goals can be used to attain long-range goals. At least four mechanisms explain why goal setting improves performance: (a) It focuses and directs activities, (b) it regulates expenditure of energy, (c) it enhances persistence because the effort is continued until the goal or subgoal is reached, and (d) it can promote the development of new strategies for improving performance. Goal setting only works if there is timely feedback showing performance or progress in relation to the goal. Goals must be accepted to be effective, and their attainment is facilitated by a plan of action or strategy. Competition can be viewed as a form of goal setting. [Edwin A. Locke (1938– ), U.S. industrial psychologist]

locked ward

locked ward a secured hospital unit in which patients with severe mental disorders reside. The present trend is toward elimination of locked wards. Factors leading to their less frequent use are improvements in psychological interventions, the use of psychoactive drugs, and the concepts of the open hospital and therapeutic community.

locked-in syndrome

locked-in syndrome a condition in which a person cannot speak or move but is fully cognizant and aware of his or her surroundings. The individual has normal metabolic functions and sleep–wake cycles but is able to communicate only with eye movements (e.g., blinking, looking up or down). Electrical activity of the brain (including event-related potentials) generally is normal as well, as demonstrated through electroencephalography, single photon emission computed tomography, and other imaging techniques. Locked-in syndrome is poorly understood and frequently misdiagnosed as coma or a vegetative state; research suggests that physicians fail to recognize signs of consciousness in more than half of cases. It is associated with disruption of motor neurons in the brainstem—typically the pons—from hemorrhage, occlusion or infarction, traumatic brain injury, tumor, encephalitis, neuromuscular disorders (e.g., amyotrophic lateral sclerosis, Guillain-Barré syndrome), and other causes. Life expectancy of an individual with locked-in syndrome may be several decades with appropriate medical care, but the probability of significant motor recovery is small. See also brain–computer interface. [term coined in 1966 by U.S. neurologists Fred Plum (1924–2010) and Jerome B. Posner]

Lockhart v. McCree

Lockhart v. McCree a case resulting in a 1986 U.S. Supreme Court decision that upheld the constitutionality of the death qualification process (see death-qualified jury) despite social science research indicating that this process produces a jury more likely to vote for conviction.

lockout

lockout n. a tactic used by an employer when negotiating a contract with a union in which employees are barred from entering the workplace and performing their jobs until they agree to the employer’s terms.

loco plant

loco plant any of certain plants belonging to the genera Astragalus or Oxytropis that grow wild in western North America, particularly in the Rocky Mountains, and that if ingested damage nerve tissue. The substances responsible include miserotoxin, swainsonine, and selenium. Symptoms of poisoning include muscular trembling or incoordination, staggering gait, and impairment of depth and other sensory perception (loco is the Spanish word for “crazy”). In sufficient doses, these toxins produce irreversible changes in the central nervous system, including brain lesions and eventual paralysis, and may cause coma or death. Also called loco weed.

locomotion

locomotion n. movement of an organism from one place to another. Different species may have different typical modes of locomotion, such as crawling, swimming, flying, bipedal walking, and quadrupedal walking. —locomotor adj.

locomotor arrest

locomotor arrest the inhibition of movement, which can be produced by volition, drugs, or electrical stimulation of the hippocampus.

locomotor ataxia

locomotor ataxia severe incoordination in walking, producing an unsteady gait. It involves degeneration of the dorsal columns of the spinal cord and is seen in individuals with neurosyphilis. See general paresis. Also called tabes dorsalis.

locomotor play

locomotor play play that involves exaggerated, repetitious movement and is physically vigorous, such as chasing, climbing, and wrestling. There are three distinctive forms: rhythmic stereotypy, exercise play, and rough-and-tumble play. Locomotor play is one of three traditionally identified basic types of play, the others being object play and social play.

locura

locura n. a culture-bound syndrome found among Latino groups in the United States and Latin America and attributed to hereditary vulnerability, the consequences of stressful and difficult life events, or a combination of the two. Symptoms include incoherence, agitation, auditory and visual hallucinations, social dysfunction, erratic behavior, and possibly violence.

locus

locus n. (pl. loci) 1. the place or position of an anatomical or pathological entity (e.g., a hemorrhage in the brain, a butterfly rash on the skin). 2. the position of a gene on a chromosome.

locus ceruleus (locus coeruleus; locus caeruleus)

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locus of causality

locus of causality attribution of the causes of an event to sources internal or external to the self, which may influence subsequent behavior in relation to that event. For example, a student who fails an exam may attribute his or her poor performance to an inherent lack of ability—an internal cause—and decide not to study at all for the next exam because “it won’t do any good,” whereas another student may attribute the same poor performance to distractions from a neighbor’s loud party during a review session the night before—an external cause—and hence study twice as long in a quiet setting for the next exam. Research suggests that consistent performance tends to be attributed to internal factors whereas highly variable performance tends to be attributed to external factors. [described in 1979 by U.S. social psychologist Bernard Weiner (1935– )]

locus of control

locus of control a construct that is used to categorize people’s basic motivational orientations and perceptions of how much control they have over the conditions of their lives. People with an external locus of control tend to behave in response to external circumstances and to perceive their life outcomes as arising from factors out of their control. People with an internal locus of control tend to behave in response to internal states and intentions and to perceive their life outcomes as arising from the exercise of their own agency and abilities. [introduced into psychology by Julian Rotter]

locus of stability

locus of stability attribution of the causes of an event sources that are constant and unlikely to change over time or to sources that are dynamic and subject to variability over time, which may influence a person’s subsequent behavior in relation to that event. For example, a supervisor who believes that an employee unexpectedly absent from a recent meeting will also miss future meetings may reprimand the person, whereas a supervisor who believes the absence is not likely to be habitual may overlook the indiscretion. [proposed in 1979 by U.S. social psychologist Bernard Weiner (1935– )]

locutionary act

locutionary act see illocutionary act.

LOD score

LOD score log of the odds score: an estimate of whether data indicate that two gene loci are linked, that is, are likely to lie near each other on a chromosome and therefore are likely to be inherited together. A LOD score of 3 or more generally indicates that the two loci are close.

loess

loess n. see local regression.

log likelihood

log likelihood the logarithm of a probability value or estimate.

log odds

log odds see logit.

log-

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log-likelihood ratio (LLR)

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log-linear analysis

log-linear analysis a method of examining relationships between two or more categorical variables that involves an analysis of the natural logarithms of frequency counts within a contingency table. Log-linear analyses do not distinguish between independent variables and dependent variables but rather attempt to model all significant associations among all variables, including interactions between any combination of the variables, using sets of odds and odds ratios for different category outcomes. Also called log-linear modeling.

log-normal distribution

log-normal distribution a theoretical distribution in which the logarithms of values on a variable follow the bell-shaped normal distribution.

logarithm (log)

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logarithmic transformation

logarithmic transformation the conversion of raw data values into another form via the use of logarithms. In turning multiplicative relationships into additive ones and eliminating exponential trends, logarithmic transformations allow researchers to analyze data using linear models. Additionally, such transformations may be used to convert raw data into a form that more closely matches the assumptions required in particular statistical analyses, particularly that of normality.

logic

logic n. 1. the branch of epistemology that is concerned with the forms of argument by which a valid conclusion may be drawn from accepted premises. As such, it is also concerned with distinguishing correct from fallacious reasoning (see fallacy). See also deductive reasoning; inference. 2. a particular rule-governed form of symbolic expression used to analyze the relations between propositions. See symbolic logic. —logical adj.

logical inference

logical inference see inference.

logical necessity

logical necessity a necessarily valid conclusion that follows from the operations of a system of formal logic on a set of premises or initial conditions.

logical paradox

logical paradox see paradox.

logical positivism

logical positivism a philosophical perspective that is committed to the principle of verification, which holds that the meaning and truth of all nontautological statements are dependent on empirical observation. In the early 20th century, the positivists of the Vienna Circle sought to establish the essential unity of logic, philosophy, and science and to distinguish these disciplines from others such as metaphysics, ethics, and religion, which were dismissed for their speculative character. The positivist view of science was influential during the period in which psychology emerged as a science and has had a recognizable influence on the discipline. This is most pronounced in behaviorism and in psychology’s commitment to empirical scientific methods. See positivism. See also physicalism; postpositivism; reductionism.

logical thinking

logical thinking thinking that is consistent with formal principles of logic. See also deductive reasoning.

logical-mathematical intelligence

logical-mathematical intelligence in the multiple-intelligences theory, the set of skills used in reasoning, abstraction, and numerical analysis and computation. These abilities are alleged to be relatively independent of the abilities involved in other types of intelligences.

logicogrammatical disorder

logicogrammatical disorder a manifestation of semantic aphasia that affects individuals with lesions of the dominant parietal lobe. An individual uses the correct words but in a sequence that gives a different meaning; for example, the words plate and table may be transposed in the sentence The plate is on the table to produce The table is on the plate.

logistic function

logistic function a basic function of the form y = c/(1 + a exp[–bx]), where y and x are variables, a, b, and c are constants, and exp is the exponential function. When graphed, values derived from a logistic function form an S shape called the logistic curve. The logistic function is used to describe longitudinal data and growth rates in particular, in which an initial stage of growth is approximately exponential and then, as saturation begins, slows and ultimately ceases altogether.

logistic regression (LR)

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logistic transformation

logistic transformation a transformation in which measurements on a linear scale are converted into probabilities between 0 and 1. It is given by the formula y = ex/(1 + ex), where x is the scale value and e is the Eulerian number. The inverse of logits, logistic transformations are used in such statistical procedures as logistic regression.

logit

logit n. a nonlinear probability function. It is given by the formula logit(p) = log(p/[1 – p]), where p is the probability of an event. In other words, a logit is the logarithm (log) of the odds of the occurrence of an event. Logits are the inverse of logistic transformations.

Logo

Logo n. a computer programming language designed at the Massachusetts Institute of Technology’s Artificial Intelligence Research Laboratory in conjunction with the research firm Bolt, Beranek and Newman to encourage the development of problem-solving skills. A dialect of LISP, Logo was directed primarily at children and is based on Jean Piaget’s research in the development of thinking. [designed by U.S. computer scientist Wally Feurzseig and South African-born U.S. mathematician Seymour Papert (1928– )]

logo- (log-)

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logogen

logogen n. a theoretical memory unit corresponding to a word, letter, or digit, which, when excited, results in the output (recognition) of the unit and recall of characteristics and information associated with that unit. For example, the logogen for table is activated by hearing the component sounds or seeing the typographical features of the word, bringing to mind such knowledge as the typical structure and shape of a table and its general function. [proposed by British psychologist John Morton (1933– )]

logographic

logographic adj. denoting or referring to writing systems that use a separate symbol (logogram or logograph) to represent each word or morpheme.

logopathy

logopathy n. a speech disorder of any kind.

logopedics

logopedics n. primarily in Britain, the study and treatment of speech disorders. See speech and language pathology.

logorrhea

logorrhea n. rapid, uncontrollable, and incoherent speech, sometimes occurring as part of a manic episode.

logotherapy

logotherapy n. an approach to psychotherapy that focuses on the “human predicament,” helping the client to overcome crises in meaning. The therapeutic process typically consists of examining three types of values: (a) creative (e.g., work, achievement), (b) experiential (e.g., art, science, philosophy, understanding, loving), and (c) attitudinal (e.g., facing pain and suffering). Each client is encouraged to arrive at his or her own solution, which should incorporate social responsibility and constructive relationships. Also called meaning-centered therapy. See also existential psychotherapy; existentialism. [developed in the 1950s and 1960s by Viktor E. Frankl]

Lokian personality

Lokian personality a personality pattern characterized by the desire to cause distress to others, manipulative behavior, and deceit. The name is derived from Loki, the Norse god of mischief.

Lolita complex

Lolita complex see nympholepsy.

London syndrome

London syndrome explicit and constant resistance and refusal by hostages to do what captors expect during a hostage situation, first identified in 1981 after a hostage-taking incident in London. It may result in serious injury and death to the resistors.

loneliness

loneliness n. affective and cognitive discomfort or uneasiness from being or perceiving oneself to be alone or otherwise solitary. Psychological theory and research offer multiple perspectives: Social psychology emphasizes the emotional distress that results when inherent needs for intimacy and companionship are not met; cognitive psychology emphasizes the unpleasant and unsettling experience that results from a perceived discrepancy (i.e., deficiency in quantity or quality) between an individual’s desired and actual social relationships. Psychologists from the existential or humanistic perspectives may see loneliness as an inevitable, painful aspect of the human condition that nevertheless may contribute to increased self-awareness and renewal. See UCLA Loneliness Scale.

long axis

long axis see axis.

long-delay conditioning

long-delay conditioning in delay conditioning, the period during which the conditioned stimulus is presented long enough to produce inhibition of delay.

long-term care

long-term care provision of health, mental health, or other services over a prolonged or extended period to someone with a chronic illness, mental illness, or disability. Care can be provided in an institutional setting or the community (e.g., at home) by health care professionals, family, or friends.

long-term care facility

long-term care facility an extended care institution, such as a nursing home, that provides medical and personal services for patients who are unable to live independently but do not require the inpatient services of a hospital.

long-term depression (LTD)

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long-term memory (LTM)

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long-term potentiation (LTP)

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long-term therapy

long-term therapy psychotherapy over a period of many months or years. Classic psychoanalysis, which may last 2–5 years or longer, is a primary example.

long-wavelength pigment

long-wavelength pigment the photopigment, present in one of the three populations of retinal cones, that has maximum sensitivity to a light wavelength of 558 nm. The absence of the gene for the long-wavelength pigment causes protanopia (red color blindness). See also medium-wavelength pigment; short-wavelength pigment.

longevity

longevity n. 1. long life. 2. the actual length of an individual’s life. See also life expectancy.

longilineal

longilineal adj. denoting a constitutional type of body that is long rather than broad and roughly equivalent to the asthenic type in Kretschmer typology.

longitudinal

longitudinal adj. 1. in anatomy, referring to the long axis of the body. 2. in research, referring to the time dimension—that is, running over an extended period.

longitudinal data

longitudinal data information obtained through multiple measurements of the same individuals over a period of time. For example, a researcher investigating the use of coping strategies in college students may evaluate stress levels at the beginning, middle, and end of the fall and spring semesters.

longitudinal design

longitudinal design the study of a variable or group of variables in the same cases or participants over a period of time, sometimes several years. An example of a longitudinal design is a multiyear comparative study of the same children in an urban and a suburban school to record their cognitive development in depth. A longitudinal study that evaluates a group of randomly chosen individuals is referred to as a panel study, whereas a longitudinal study that evaluates a group of individuals possessing some common characteristic (usually age) is referred to as a cohort study. Also called longitudinal research; longitudinal study. Compare cross-sectional design.

longitudinal fissure

longitudinal fissure a deep groove that marks the division between the left and right cerebral hemispheres of the brain. At the bottom of the groove, the hemispheres are connected by the corpus callosum. Also called interhemispheric fissure; sagittal fissure.

longitudinal stability

longitudinal stability the degree to which an individual’s possession or expression of a psychological characteristic is consistent over a period, as compared with other people.

look angle

look angle in ergonomics, the direction in which the operator looks during task performance. The goal is to design equipment and workstations in such a way that the viewing angle is central or forward rather than requiring head movements or eye glances to the left or right. See also head-up display.

look-say

look-say n. see whole-word method.

looking-glass self

looking-glass self a self-concept formed by incorporating other people’s views of oneself into one’s own self-views. The term suggests a self-concept that is, in part, a reflection of other people’s impressions, reactions, and opinions. See reflected appraisals; symbolic interactionism. [introduced by U.S. social thinker Charles Horton Cooley (1864–1929)]

looming

looming n. a type of space perception in which the retinal image of an object is magnified as the object approaches the observer. Reactions to looming vary: Chicks run away, kittens avert their heads, monkeys leap backward while making alarm cries, and human infants attempt to withdraw their heads at 2 weeks and blink at 3 weeks.

loose culture

loose culture a heterogeneous social group whose diverse members tend to value originality, risk taking, and a flexible adherence to the collective norms of their culture or group. Compare tight culture. [coined by Greek-born U.S. psychologist Harry C. Triandis (1926– )]

loosening of associations

loosening of associations a thought disturbance demonstrated by speech that is disconnected and fragmented, with the individual jumping from one idea to another unrelated or indirectly related idea. It is essentially equivalent to derailment.

loperamide

loperamide n. an opioid that slows gastrointestinal motility and is used for the treatment of diarrhea. Because it is not effectively transported across the blood–brain barrier, it has few (if any) psychotropic effects and its abuse potential is low. U.S. trade name: Imodium.

lorazepam

lorazepam n. a highly potent benzodiazepine approved for the treatment of anxiety and as premedication in surgical anesthesia. Unlike many other benzodiazepines, it has no active metabolic products and therefore requires minimal processing in the liver. This, together with its predictable duration of action, make it a favored drug in the management of alcohol withdrawal in patients with liver impairment. U.S. trade name (among others): Ativan.

Lord’s paradox

Lord’s paradox an effect in which the relationship between a continuous outcome variable and a categorical independent variable (e.g., treatment or control) is reversed when an additional covariate is introduced to the analysis. For example, suppose that a researcher is studying change in knowledge about a topic following an intervention and obtains results indicating that those who received the treatment had a better outcome (i.e., had learned more) than those in the control group. If, however, the researcher decides to use an analysis of covariance to adjust the treatment effect according to general educational level, the pattern of findings could be reversed: If participants receiving the treatment had a substantially higher level of education than those in the control group, it might now appear that they did not gain from the intervention. [Frederick M. Lord]

lordosis

lordosis n. 1. an abnormal inward curvature of the spine in the lumbar and cervical regions. In extreme cases, the condition is known as hyperlordosis. See also kyphosis; scoliosis. 2. in many rodents, a similar but normal posture that is assumed by females during periods of sexual receptivity and serves to facilitate copulation with a male. In the absence of lordosis, males are physically unable to mate with the female. See presenting.

Lorenzini ampullae

Lorenzini ampullae see electric sense.

LOS

LOS abbreviation for length of stay.

loser effect

loser effect in many species, the reduced likelihood that an individual will win future contests over resources after repeated experiences of losing in such contests. Physiological changes, such as increased glucocorticoids (e.g., cortisone, cortisol) or decreased testosterone, often occur with the loser effect. Compare winner effect.

loss aversion

loss aversion see behavioral economics.

loss of affect

loss of affect loss of the ability to respond emotionally, which results in flat affect.

loss of consciousness (LOC)

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lost letter procedure

lost letter procedure an indirect attitude measure used at an aggregate group level. Two sets of stamped envelopes are created, one addressed to a group likely to adopt a particular attitudinal position on the target issue and the other addressed to a group likely to adopt the opposite position. Equal numbers of each version of the envelope are randomly distributed in a particular community. The procedure is based on the logic that a person finding a letter that has apparently been inadvertently dropped is more likely to place the letter in a mailbox if it is addressed to a group that shares his or her position. The percentage of people in that community supporting the two positions is then inferred from the number of envelopes that are ultimately mailed to each address. Also called lost letter technique. [originally developed by Stanley Milgram]

lot acceptance sampling

lot acceptance sampling see acceptance sampling.

Lou Gehrig’s disease

Lou Gehrig’s disease see amyotrophic lateral sclerosis. [Henry (Lou) Gehrig (1903–1941), U.S. baseball player who died of the disease]

loudness

loudness n. the subjective magnitude of sound. It is determined primarily by intensity but is also affected by other physical properties, such as frequency, spectral configuration, and duration. The unit proposed for loudness is the sone: One sone is defined as the subjective magnitude of a 1 kHz tone presented at 40 dB SPL (decibels sound-pressure level), based on loudness judgments by listeners. Loudness approximately doubles for each 10 dB increase in intensity. The loudness level is the level in decibels SPL of a 1 kHz tone that is judged to be equally as loud as the test sound. The unit is the phon: A sound whose loudness level is 40 phons has a loudness equal to that of a 1 kHz tone presented at 40 dB SPL.

loudness summation

loudness summation a situation in which the loudness of different sounds presented together is the sum of their individual loudnesses. For example, if Sound A at 40 dB SPL (decibels sound-pressure level) has a loudness of 1 sone and Sound B at 50 dB SPL has a loudness of 2 sones, then loudness summation is said to occur if the loudness of A and B presented together is 3 sones. Loudness summation depends on the frequency composition of the sounds. See also critical band.

Louis-Bar syndrome

Louis-Bar syndrome see ataxia telangiectasia. [Denise Louis-Bar (1914– ), Belgian neuropathologist]

love

love n. a complex emotion involving strong feelings of affection and tenderness for the love object, pleasurable sensations in his or her presence, devotion to his or her well-being, and sensitivity to his or her reactions to oneself. Although love takes many forms, including concern for one’s fellow humans (brotherly love), parental love, erotic love, self-love, and identification with the totality of being (love of God), the triangular theory of love proposes three essential components: passion, intimacy, and commitment. Social psychological research in this area has focused largely on passionate love, in which sexual desire and excitement predominate, and companionate love, in which passion is relatively weak and commitment is strong.

love need

love need in Maslow’s motivational hierarchy, the third level of the hierarchy of needs, characterized by the striving for affiliation and acceptance. Also called social need.

love object

love object 1. the person toward whom an individual directs affection, devotion, and (usually) sexual interest. 2. in psychoanalytic theory, the person who is loved by the individual’s ego, as opposed to the object that satisfies an instinct.

love scale

love scale a measure of the strength of one person’s feeling of love for another. Because love is a complex state occurring in many different forms, the various scales that have been devised do not always recognize the same components of this multifaceted emotion. As examples, the measure assessing passionate love developed by U.S. social psychologist Elaine Hatfield (1937– ) concentrates on items dealing with sexual desires as well as other, more cognitively oriented items, reflecting a preoccupation with the love object and idealization of this person, whereas the romantic love scale devised by U.S. social psychologist Zick Rubin (1944– ) involves elements of both passionate and companionate love and includes items dealing with willingness to confide in the loved person and the desire to be with him or her. See also liking scale.

love withdrawal

love withdrawal a form of discipline in which parents threaten to withdraw their love and affection from children if they misbehave.

lovemap

lovemap n. a person’s mental image of the ideal lover, the ideal love relationship, and ideal sexual activity with the partner, expressed in fantasy and in actual sexual behavior. It incorporates issues of sexual orientation and also of desire for deviant behaviors (see paraphilia). [proposed by John Money]

low birth weight (LBW)

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low normal

low normal see below average.

low threshold

low threshold see high threshold.

low vision

low vision reduction of visual capacity (especially visual acuity and visual field), regardless of the underlying cause, that cannot be corrected to the normal range with glasses, contact lenses, or medical or surgical treatment. Low vision causes problems with various aspects of visual performance (e.g., mobility, reading) and is often associated with a decline in quality of life, an increased risk of depression, and decreased functional status. Low vision services provided to those with this condition include assessment of an individual’s residual vision and instruction in the use of high-powered optical devices (see vision rehabilitation). Also called partial sight. See also blindness; visual impairment.

low-ball technique

low-ball technique a procedure for enhancing compliance by first obtaining agreement to a request and then revealing the hidden costs of this request. Compliance to the target request is greater than would have been the case if these costs had been made clear at the time of the initial request. See also door-in-the-face technique; foot-in-the-door technique; that’s-not-all technique.

low-functioning autism (LFA)

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low-pass filter

low-pass filter see filter.

low-technology assistive device

low-technology assistive device a device using inexpensive, widely available technology to increase, maintain, or improve the functional capabilities of individuals with disabilities. An example is an eating utensil with a built-up handle. See assistive technology.

Lowe syndrome

Lowe syndrome see oculocerebrorenal syndrome.

lower hinge

lower hinge the point in a distribution of values below which lie one fourth of the data. It is equivalent to the first quartile and lies midway between the median and the minimum point of the distribution. Compare upper hinge.

lower motor neuron

lower motor neuron see motor neuron.

lower quartile

lower quartile see quartile.

lower real limit

lower real limit see real limit.

lowess

lowess n. see local regression.

loxapine

loxapine n. an antipsychotic introduced into the U.S. market in the early 1970s. Loxapine differs from the conventional antipsychotics in that it binds strongly to serotonergic as well as dopaminergic receptors. Although its chemical structure (see dibenzoxazepine) is similar to that of the atypical antipsychotic clozapine, loxapine has the same antipsychotic, antiemetic, sedative, and extrapyramidal properties as the conventional antipsychotic agents. U.S. trade name: Loxitane.

loyalty

loyalty n. faithfulness and allegiance to individuals or social groups. —loyal adj.

LPAD

LPAD abbreviation for Learning Potential Assessment Device.

LPC Scale

LPC Scale abbreviation for Least Preferred Coworker Scale.

LPN

LPN abbreviation for licensed practical nurse.

lPOA

lPOA abbreviation for lateral preoptic area.

LR

LR n. abbreviation for likelihood ratio. LR abbreviation for logistic regression.

LRE

LRE abbreviation for least restrictive environment.

LRP

LRP abbreviation for lateralized readiness potential.

LSD

LSD 1. lysergic acid diethylamide: a highly potent hallucinogen that structurally resembles the neurotransmitter serotonin and presumably exerts its psychoactive effects by acting as a partial agonist at the 5-HT2A serotonin receptor. It was originally synthesized from the ergot alkaloid lysergic acid in 1938 by Swiss chemist Albert Hoffman, who then discovered its hallucinogenic effects on accidental ingestion in 1943. At very low doses, it is capable of producing visual distortions (sharpened sense of color) or frank hallucinations, together with feelings of euphoria or arousal; it became a widely used and controversial recreational drug during the mid-1960s and early 1970s. The effects of LSD were the subject of research during the 1950s as a possible model for psychosis, and various attempts were made during the 1950s and 1960s to use LSD as an aid to psychotherapy (see psychedelic therapy), although they did not prove effective. The drug is usually taken orally. 2. abbreviation for least significant difference. See Fisher least significant difference test.

LTD

LTD abbreviation for long-term depression.

LTH

LTH abbreviation for luteotropic hormone. See prolactin.

LTM

LTM abbreviation for long-term memory.

LTP

LTP abbreviation for long-term potentiation.

lucid dream

lucid dream a dream in which the sleeper is aware that he or she is dreaming and may be able to influence the progress of the dream narrative.

lucid interval

lucid interval a period of mental clarity following a period of delirium, disorganization, or confusion brought on by a mental condition, such as a psychotic state.

lucidity

lucidity n. a mental state in which a person may not have the complete ability to reason or comprehend complex matters but has adequate mental powers to be legally responsible for his or her actions. —lucid adj.

Lucifer effect

Lucifer effect the tendency for iniquitous social contexts to negatively influence and transform human behavior, in some cases to an extreme degree (see power of the situation). According to this conceptualization, even individuals who are inherently moral in character and upbringing can, in a corruptive social setting, be induced to act dishonorably and unethically. This phenomenon takes its name from the Christian story of the angel Lucifer, who defied God’s authority and ultimately became the Devil. See also Stanford prison study. [coined by U.S. psychologist Philip G. Zimbardo (1933– ) in his 2008 book The Lucifer Effect: Understanding How Good People Turn Evil]

lude

lude n. slang for methaqualone.

Ludiomil

Ludiomil n. a trade name for maprotiline.

lues

lues n. syphilis. The name may be combined with an anatomical or other term, for example, lues nervosa for syphilis of the nervous system. —luetic adj.

lumbar

lumbar adj. referring to the lower part of the back or spinal cord.

lumbar nerve

lumbar nerve see spinal nerve.

lumbar puncture

lumbar puncture a procedure used to obtain a sample of cerebrospinal fluid for diagnostic purposes by inserting a needle into the subarachnoid space of the spinal cord at a point between two lumbar vertebrae. Also called spinal tap.

lumbosacral plexus

lumbosacral plexus a network of nerve fibers derived from the spinal roots of the fourth and fifth lumbar nerves and first through fourth sacral nerves (see spinal nerve). It supplies the muscles of the leg and foot. The largest derivative of the lumbosacral plexus is the sciatic nerve. Also called lumbrosacral plexus.

lumen

lumen (symbol: lm) n. the unit of luminous flux equal to the flux emitted by a uniform point source of 1 candela in a solid angle of 1 steradian.

Luminal

Luminal n. a trade name for phenobarbital.

luminance

luminance n. the amount of light reflected or emitted from an object as measured in candelas per square meter.

luminosity

luminosity n. the visual sensation of the brightness of a light source. It depends on the power emitted by the source and on the sensitivity of the eye to different wavelengths of light. Other factors can also influence the luminosity; for example, a light of a given luminous intensity will appear brighter in a room with white walls than in a room with dark walls.

luminosity coefficient

luminosity coefficient see coefficient of visibility.

luminosity curve

luminosity curve a graph of visual sensitivity (perceived luminosity) as a function of the wavelength of light.

luminous flux

luminous flux (symbol: Φv) the rate at which light is emitted from a source or reflected from a surface. It is measured in lumens by reference to a standard source.

luminous intensity

luminous intensity (symbol: Iv) the luminous flux emitted per unit solid angle by a point source in a given direction, measured in candelas.

lunacy

lunacy n. 1. an obsolete name for any mental illness. 2. in legal use, an obsolete name for mental incompetence or legal insanity. 3. the theory that some forms of mental illness correspond with the phases of the moon. See also moon-phase studies. —lunatic adj., n.

lunatic asylum

lunatic asylum see insane asylum.

Lunesta

Lunesta n. a trade name for eszopiclone.

Lupron

Lupron n. a trade name for leuprolide.

lupus erythematosus (LE)

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lurasidone

lurasidone n. an atypical antipsychotic of the benzoisothiazol derivative class that is thought possibly to exert its effect by acting as a serotonin 5-HT2A and dopamine D2 receptor antagonist. It is used in the treatment of schizophrenia. U.S. trade name: Latuda.

lure

lure n. an incorrect item presented among correct items in testing memory, to serve as a distractor.

Luria–Nebraska Neuropsychological Battery (LNNB)

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lurking variable

lurking variable see hidden variable.

lust murder

lust murder an extreme form of sexual sadism in which an individual experiences sexual arousal from the murder of a partner during the sexual act, often including elaborate staging of the act and mutilation of the victim’s body. Also called erotophonophilia. See also homicidophilia.

luteal phase

luteal phase see menstrual cycle.

luteinizing hormone (LH)

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luteotropic hormone

luteotropic hormone see prolactin.

luteotropin

luteotropin n. see prolactin.

Luvox

Luvox n. a trade name for fluvoxamine.

lux

lux n. the standard unit of illuminance, equal to the illumination produced by a luminous flux of 1 lm (lumen) per square meter.

LVN

LVN abbreviation for licensed vocational nurse. See licensed practical nurse.

LVP

LVP abbreviation for lysine vasopressin.

lycanthropy

lycanthropy n. 1. the supposed transformation of a human being into a wolf or other animal (from Greek lykos, “wolf”). Belief in lycanthropy reached epidemic proportions in Europe during the 16th century, when 600 supposed lycanthropes were sentenced to death for having committed violent crimes in animal form. Also called lycomania; zoanthropy. 2. a condition in which a person has delusions that he or she is or can become a wolf or other animal.

lygophilia

lygophilia n. an abnormal desire to be in dark or gloomy places.

Lyme disease

Lyme disease a multisystemic illness caused by spirochete bacteria transmitted through the bite of an infected deer tick. Initial effects are a red rash around the site of the bite as well as flulike symptoms of fever, fatigue, headache, and body aches. If left untreated, the disease can result in arthritis; neurological symptoms (e.g., severe headache, temporary paralysis); mood changes; and problems with memory loss, concentration, and sleep. Its manifestation of physical, cognitive, and psychiatric symptoms makes it difficult to diagnose. The disease was first recognized in 1975 after a large number of children in Lyme, Connecticut, were initially diagnosed with rheumatoid arthritis.

lymphocyte

lymphocyte n. a type of blood cell (see leukocyte) that plays a key role in specific immune responses. There are two main classes. B lymphocytes (or B cells), which develop and mature in the bone marrow, are responsible for humoral immunity: They produce circulating antibodies when they bind to an appropriate antigen and are costimulated by certain T cells. T lymphocytes (or T cells), which mature in the thymus, are responsible for cell-mediated immunity: They are characterized by the presence of particular cell-surface molecules and are capable of antigen recognition. There are two main subclasses: cytotoxic T cells, which release proteins that destroy invading cells, and helper T cells, which assist in this or other aspects of the immune response. See also natural killer cell. —lymphocytic adj.

lymphokine

lymphokine n. any of a group of proteins, secreted by lymphocytes, that have a role in cell-mediated immunity by inducing other cells of the immune system to divide. See cytokine.

lynching

lynching n. an instance of a group or mob of vigilantes killing a person, especially by hanging. The lynch mob often justifies its actions by claiming that the victim is guilty of some crime and the group is administering an appropriate punishment. Most lynchings in the United States were racially motivated acts of violence perpetrated by White Americans against African Americans. The first documented U.S. lynching occurred in 1882; by 1950, lynch mobs had killed more than 3,000 people. —lynch vb.

lysergic acid diethylamide

lysergic acid diethylamide see LSD.

lysine

lysine n. an essential amino acid that cannot be synthesized by the body and must be supplied in the diet. It is often added to human or nonhuman animal foods to improve their nutritive value.

lysine vasopressin (LVP)

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lysinuric protein intolerance

lysinuric protein intolerance an autosomal recessive metabolic disorder caused by mutations in the SLC7A7 gene and characterized by the body’s inability to digest and use the amino acids lysine, arginine, and ornithine. Symptoms usually develop after infants begin to eat solid foods. Early signs include nausea and vomiting after ingestion of protein-rich foods. Enlarged liver and spleen, short stature, muscle weakness, osteoporosis, and a life-threatening lung disorder are also associated with this condition.

lysis

lysis n. the gradual subsidence of the symptoms of a disease or disorder. Compare crisis.

lysosome

lysosome n. see phagocytosis.

Psychology Terms Starting With 'L'