Abstract
We investigated the color properties of binocular color fusion and rivalry, in order to determine whether the between-eye colour difference needed to produce rivalry was dependent on a) the average colour and b) the colour contrast of the stimuli. The stimuli were two, 4.57-deg diameter, circular colour patches, presented on an equiluminant grey background, separately presented to each eye via a modified Wheatstone sterescope, and for 1500 ms. The task was to decide whether the stimulus appeared fused or rivalrous, and the colour-rivalry threshold was defined as the angular difference between the two colours required to just produce rivalry. The chromaticities of the stimuli were defined according to a scaled version of the MacLeod-Boynton color space, and the luminance and color contrasts of the stimulus pairs were equated using a matching procedure. We found that color rivalry thresholds were approximately uniform at around 45 deg, irrespective of whether centered around the cardinal colors, the unique hues or the binary hues. This suggests that binocular color fusion involves multiple-color mechanisms at the postreceptoral level. There were no significant differences in color rivalry thresholds between different colour contrast levels, suggesting that contrast (saturation) is not a defining factor for binocular color fusion and rivalry.
Supported by Canadian Institute of Health Research grant #MOP-11554 awarded to FK.