Metacontrast reveals asymmetries at red–green isoluminance

We examined the spatiotemporal response of the visual system to red–green isoluminant stimuli by using two metacontrast masking paradigms. With both, we found that green stimuli surrounded by red fields, as compared with red stimuli surrounded by green fields, yielded weaker metacontrast masking. These results run counter to those of models of metacontrast and spatiotemporal vision that predict the same magnitude of metacontrast for the two stimulus-surround cases. Possible visual processes associated with the obtained asymmetries at red–green isoluminance are discussed.