Numerous studies have shown that sensitivity to binocular targets is higher than to its monocular components, a phenomenon known as binocular summation. Binocular summation has been demonstrated with luminance contrast targets that are not only interocularly in-phase, that is, identical in both eyes, but also interocularly anti-phase, that is, of opposite polarity in the two eyes. Here we show that for the detection of anti-phase targets defined along the red–cyan and violet–lime axes of cardinal color space two eyes are more often than not worse than one. We suggest this is because channels that detect interocular differences, or S− channels are relatively insensitive to chromatic stimuli. We tested this idea by measuring binocular summation for chromatic anti-phase targets in the context of a chromatic surround that itself was either interocularly in-phase or anti-phase. The anti-phase surrounds reduced even further binocular summation for the anti-phase targets whereas the in-phase surrounds increased the level of summation. We show that a model that combines via probability summation the independent activities of adding S+ and differencing S− channels gave a good account of the data, especially for the anti-phase targets. We conclude that binocular adding and differencing channels play an important role in binocular color vision.
Kingdom et al. (Thu,) studied this question.