Abstract
Between-eye difference thresholds (BEDTs) were measured for hue and saturation using dichoptically superimposed coloured patches. BEDTs were measured at isoluminance and as a function of added binocular (i.e. same in both eyes) luminance contrast, both increments and decrements. Increasing the binocular luminance contrast increased BEDTs for both hue and saturation. A control experiment showed that the BEDTs were only elevated when the binocular luminance contrast was spatially coextensive within the colour-defined patches. When measured under full binocular viewing conditions however, i.e. when each member of the dichoptic pair was presented at a separate screen location and to both eyes, both hue and chromatic contrast difference thresholds were unaffected by the addition of binocular luminance contrast. These results are hard to explain by the simple dilution of the colour signals by luminance contrast, as thresholds were only elevated in the dichoptic viewing conditions. A model of BEDTs that includes an interocular suppression component whose gain is inversely proportional to the amount of binocular luminance contrast was found to give a good account of the data.