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Abstract:
Adaptation to a steady background has a profound effect on both colour appearance and discriminability. We determined the temporal characteristics of adaptation for appearance and discrimination, and for changes along different colour directions. Subjects were adapted to a large uniform background made up of a CRT screen and a 60 deg × 60 deg wall illuminated by computer-controlled lamps. After an instant change in background colour along the red - green or blue - yellow cardinal colour axes, we measured thresholds for the detection of increments or decrements along the same axes at fixed times between 16 and 120 s. Analogously, colour appearance was determined by means of observer production of achromatic appearance. We found a slow exponential time-course of adaptation with a half-life of 20 - 30 s that was common to appearance and discrimination. Also, a 50 - 100 ms component could be identified, which was probably due to photoreceptor adaptation. There was an extremely fast mechanism with a half-life faster than 10 ms, but only for colour appearance. There were no differences for adaptational changes along the different colour axes. We conclude that the fast adaptation mechanism for colour appearance is of higher order and is situated after the mechanisms mediating slower adaptational changes in colour discrimination and appearance.
