1. a putative process or entity in the mind or the nervous system whose operations are invoked to explain some aspect of human behavior or experience. The problem with such theories is that the behavior or experience of the homunculus usually requires explanation in exactly the same way as that of the person as a whole. As a result, homunculus theories tend to end in circular reasoning. For example, to explain its theory that certain ideas are kept from conscious awareness because they are threatening to the person, psychoanalysis must posit some specialized part of the person that is aware of the ideas and knows that they are threatening. Similarly, some information-processing theories invoke a “decision-making process” to explain the making of decisions. Both theories invoke a sophisticated level of inner awareness or processing in an attempt to explain another outward level of awareness or processing. For this reason, critics would say that they require homunculi, or that they commit the homunculus fallacy.

2. in neuroanatomy, a figurative representation, in distorted human form, of the relative sizes of motor and sensory areas in the brain that correspond to particular parts of the body. For example, the brain area devoted to the tongue is much larger than the area for the forearm, so the homunculus has a correspondingly larger tongue. See motor homunculus; sensory homunculus.

3. a completely formed minute human figure (Latin, “little man”) thought by some 16th- and 17th-century theorists to exist in the spermatozoon and simply to expand in size during the transition from zygote to embryo to infant to adult. This idea is an example of preformism and is contrary to the epigenetic principle of cumulative development and successive differentiation. —homuncular adj.