Abstract
This study investigated whether visual processes selective to both color and orientation contribute to resolution of binocular rivalry, by taking advantage of the previous finding that binocular preceding stimuli of long duration phenomenally suppress one of the rivalrous stimuli having the same stimulus attribute. Specifically, this study asked how binocular rivalry between dichoptic chromatic gratings having the same color but different orientations (e.g., green/gray right-tilted vs. green/gray left-tilted gratings) would be affected by a preceding chromatic grating also having the same color (e.g., green/gray right-tilted grating) or by the one having a different color (e.g., red/gray right-tilted grating). If color-orientation selective processes contribute to rivalry resolution, modulative effects of the preceding stimulus should be larger when the combination of color and orientation in the preceding stimulus was the same as that in one of the rivalrous stimuli, even when the stimulus color was not relevant to binocular rivalry. In the experiment, 2 c/deg square-wave gratings were used as stimuli whose mean luminance was 4 cd/m2 and Michelson contrast was 0.60. The duration of the preceding stimulus was 1 sec and that of rivalrous stimuli was 200 msec. In addition to the orientation-rivalry condition described above, the color-rivalry condition was also designed using the similar principle. Results under the orientation-rivalry condition showed no effect of the color-orientation combination; a strong modulative effect of the preceding stimulus was found but its magnitude did not change depending upon whether the preceding stimulus had the same color as the rivalrous stimuli. Under the color-rivalry condition, however, a small difference due to the color-orientation combination was found. These results suggest that the dominance/suppression of rivalrous chromatic gratings is mainly determined by visual processes responding separately to color and orientation. A small contribution of color-orientation selective processes could be found only over limited conditions.