Contrast additivity: An alternative approach

Abstract

Several investigators have demonstrated luminance additivity when subjects are required to detect the presence of abrupt luminance discontinuities (“edges”) in chromatically mixed fields. Experiment I shows that this result occurs for stimuli other than edges. Low and high frequency and contrast sine wave gratings approximate additivity more than homogeneous fields. Experiment II shows that additivity of contrast detection is destroyed when the B-W system is fatigued by a black and white grating. This non-additive result is explained within an opponent process model assuming that contrast detectors pool information from chromatic and B-W systems. The model can also explain additive results during conditions in which the B-W system is not fatigued.