Abstract
[Purpose] Visibility of rivalrous flashes can be modulated by presenting a preceding stimulus (visibility modulation, VM). Previously, we showed that the characteristics of VM were different for color and pattern stimuli and suggested that dominance and suppression of rivalrous binocular inputs are determined in distinct fashions for color and pattern (Abe et al., VSS2007). The present study investigated VM with chromatic gratings to explore how color and pattern are integrated in the visual processes mediating VM.
[Methods] The rivalrous test stimulus was composed of green/gray right-tilted and red/gray left-tilted square-wave gratings of 2 c/deg presented dichoptically on a black background (0.1 cd/m2). Mean luminance of the stimulus was 4 cd/m2 and luminance contrast was 90 or 0 %. The preceding stimulus was identical to one of the test stimulus in the same-combination condition, whereas color from one of the test stimulus was combined with pattern from the other in the different-combination condition.
[Results and Discussion] When luminance contrast was high, the color-pattern combination in the preceding stimulus strongly affected how VM occurred: Stimulus-based VM was observed under the same-combination condition (i.e., the test stimulus of the same attributes was phenomenally suppressed by the preceding stimulus), while eye-based VM was observed under the different-combination condition (i.e., the ipsilateral stimulus was suppressed). On the other hand, when the gratings were isoluminant and the test duration was long, the effect of the color-pattern combination was much reduced and the results could be mostly explained by color-based VM. Moreover, when the test duration was short, VM became eye-based and misbinding of color and pattern (e.g., red/green stripe) was also often observed. These findings suggest that VM for color, pattern, and the combination of the two can be determined in different fashions, which is consistent with the contribution of competition interactions at multiple neural sites.