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Abstract

Chromatic adaptation and induction are usually described by two-process models (Ware Cowan, 1982). At the initial stage of these models, the sensitivities of the three cone
types are adjusted (von Kries, 1905). According to a more recent investigation, adaptation
may be explained by just these gain changes (Chichilnisky Wandell, 1995). The
second stage of these models consists of mutually inhibitory interactions within the chromatic
mechanisms.
By use of heterochromatic flicker photometry and detection experiments a special color
metric is developed: stimuli of equal brightness with an amplitude at 5-fold detection
threshold to the white point in the center of cone contrast space are specified by one parameter,
their azimuth. At detection threshold, the three cone contrasts and also the excitations
of the chromatic mechanisms are sinusoidal functions of this azimuth. The three
cone contrast functions yield zero-crossings at different angles and so do the chromatic
mechanisms. Using an infield-surround stimulus this phase information allows to distinguish
between gain changes at the receptors and opponent interactions within the chromatic
mechanisms.
S-cones are found to influence brightness and red-green detection. Binocular presentation
of the infield-surround stimulus reveals that chromatic induction is mediated by interactions
within the opponent chromatic mechanisms. No adaptational components are required
to explain the binocular results. Dichoptic presentation reveals global gain controls
at the receptor level in addition to the local opponent interactions obtained in the
binocular experiments.