Index A Abney effect, 167 absorption spectra, 109, 241 acetylcholine, 41, 57 muscle fibers' sensitivity to, 44-45 achromatic, 241 action potential, 5, 7, 241 activity, effect on nervous system, 42-45 acuity, 241 adaptation, 241 Adelson, Ted, 123 Adler, Julius, 32 afferent neuron, 241 Andersen, Per, 43 Andrews, Tim, 100, 103 angiogenesis, 20 angles, geometry perception, 191-197 aperture problem, 242 apertures defined, 242 occluding apertures, 204, 208-215 artificial intelligence, 242 artificial neural networks, 242. See also neural networks association areas, response to faces, 119 association cortex, 242