The Colors Produced by Equilibrium Photopic Adaptation.

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Abstract
Reports experiments on Hering's theory that equilibrium adaptation of the retina to any stimulus produces a sensation of neutral gray. Studies on achromatic stimuli indicated that the initial dazzling brightness rapidly decreased to around one twentieth its original intensity, and remained at this intensity throughout the remainder of the period of exposure. Any nearer approach to a neutral grey could not be observed. Similar experiments with colors revealed no permanent disappearance of the original hue, although there was marked decrease in saturation and brightness. Similar results were obtained with chromatic stimuli of exceedingly high intensity. These results suggest that the equilibrium sensation is not neutral grey, but that it varies widely with the conditions under which adaptation is established.Hering's theory explains that spot stimuli fluctuate under adaptation due to eye-movement and consequent differential recovery of the retina. However, in the case of large angle stimuli, where recovery by eye-movement is impossible, the explanation may be the size and activity of the pupil, which is capable of varying from 7.5 mm. to 1.5 mm.In experiments to determine the role played by the pupil, pupillary contractions coincided with the disappearance signals in every series of observations. In an experiment with an artificial pupil, the number of fluctuative disappearances in several thousand observations was negligible. This suggests that variations in the size of the natural pupil are responsible for fluctuations of sensations of supraliminal sensory equilibrium.Stimuli of low intensity may disappear below the threshold by adaptation, but supraliminal equilibrium sensations do not adapt out permanently to neutral grey. From Psych Bulletin 19:03:00181. (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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