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methylxanthine

n. any of a group of methylated derivatives of xanthines (stimulant plant alkaloids) with similar pharmacological actions. The most common are caffeine (1,3,7-trimethylxanthine), the active ingredient in coffee; theobromine (3,7-dimethylxanthine), the active ingredient in cocoa; and theophylline (1,3-dimethylxanthine), the active ingredient in tea. At low doses, methylxanthines cause CNS stimulation and arousal; at high doses, anxiety, agitation, and coma may result. Methylxanthines also relax bronchial muscles: Some (e.g., theophylline) have been used in the medical management of reactive airway disease, although they have now largely been supplanted by newer agents.

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Psychology term of the day

February 22nd 2025

emergent feature

emergent feature

an entity produced by the interaction of small or simple elements (e.g., short line segments) in the visual system, such an entity (e.g., a polygon) being more salient to human perception than are the elements themselves. In ergonomics, object displays are usually designed to make use of emergent features; the display configurations yield an overall image (e.g., a rectangle or pentagon) that can be perceived holistically by the operator of a machine system and therefore rapidly analyzed to assess the state of the system. When a component of the system is not in the appropriate or normal state, the image will be distorted, alerting the operator to potential problems.