Abstract

The Pi-4 color mechanism was isolated in three observers with a 500-nm, 200-msec, 1-deg foveal test flash. Stiles’s field displacement law was tested with increment thresholds upon monochromatic adapting fields of several wavelengths. The data of all three observers reject the displacement law. Data that use a 10-msec-duration test flash likewise reject the displacement law. We conclude that the Pi-4 branch represents light adaptation controlled by more than one class of cone. A model of the Pi-4 detection pathway is proposed that quantitatively describes the increment-threshold data.

© 1982 Optical Society of America

Stiles’s Π₅ color mechanism: Tests of field displacement and field additivity properties

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