Abstract

When a purely chromatic stimulus (foveal 1° test on uniform field) is accompanied by a spatially coincident luminance change, the threshold for chromatic detection is about half of what it is without the luminance pedestal. Here we report experiments in which the test and pedestal are varied in duration and separated in time. With a 30-ms pedestal and a 200-ms test, the pedestal must precede the test by <100-ms SOA or facilitation does not occur. Maximum facilitation is reached at or slightly after test onset, and when the pedestal is presented near the end of the test flash, masking occurs rather than facilitation. The masking indicates a powerful rebound or chromatic contrast effect induced by the offset of these very weak chromatic test lights. The perception of test and pedestal presentations as a single event is necessary but not sufficient for facilitation to occur. These results may be used to constrain theories of how luminance contours can improve chromatic discrimination.

© 1987 Optical Society of America