Müller-Lyer illusion

a geometric illusion in which a difference is perceived in the length of a line depending on whether arrowheads at either end are pointing toward each other or away from each other. Also called arrowhead illusion. [first described in 1889 by Franz Müller-Lyer (1857–1916), German psychiatrist and sociologist]

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Psychology term of the day

February 1st 2025

A fiber

a myelinated nerve fiber (axon) of the somatosensory system. A fibers are subdivided by diameter, ranging from largest to smallest: A-alpha fibers are 13 to 20 μm in diameter and transmit information from proprioceptors of skeletal muscles, A-beta fibers are 6 to 12 μm and transmit information from mechanoreceptors of the skin, and A-delta fibers are 1 to 5 μm and transmit temperature and sharp pain information. See also B fiber; C fiber.