Abstract

The effect of background orientation, as well as stimulus alignment, background spatial frequency, and background contrast on simultaneous contrast effects, was observed in achromatic displays of plus-sign-shaped test stimuli against square-wave gratings. Results indicated that the axis along which lightness information most influences contrast induction varies depending on background orientation and spatial frequency. When background spatial frequency was higher than that of the test pattern, contrast induction was influenced most by neighboring elements on the axis perpendicular to the background orientation. When spatial frequency was equivalent to that of the test stimulus and test stimulus arms were aligned with similar-luminance background stripes, induction was influenced more by information along the same axis as the background orientation. When test stimulus arms were aligned with most-dissimilar background stripes, judgments were again most influenced along the axis perpendicular to the background orientation. Bias of judgment in each direction increased as the background contrast approached that of the test stimulus arms. Traditional explanations of simultaneous contrast based on lateral inhibition at the retina are found to be incomplete. Accounts for the observed effects based on local surrounding luminance and on the nature of orientation-specific cell connections are outlined.

© 1988 Optical Society of America