Abstract
When two dissimilar flashes are presented dichoptically, observers usually experience binocular rivalry. Without changing the rivalrous flashes themselves, their visibility can be modulated by presenting a monocular stimulus prior to the rivalrous flashes (visibility modulation, VM). The VM has been demonstrated, mainly with spatial patterns, to occur in an eye-specific fashion (“flash suppression”; Wolfe, 1984, Vision Research), but also in a stimulus-specific fashion (Ikeda & Morotomi, 2000, Psychologia). To elucidate further the nature of the VM, we investigated it using rivalrous red and green flashes by systematically varying temporal parameters of the preceding and test stimuli. We found that the VM occurred with preceding stimuli of longer duration (> 200 msec). Moreover, it occurred mostly in a stimulus-specific fashion; e.g., a green preceding stimulus phenomenally suppressed a green flash regardless of the eye to which it was presented, and thus the test flash appeared predominantly red. Eye-specific VM was observed only when the test duration was short (around 30 msec) and the ISI was also short (< 50 msec). Because similar modulation could not be observed when only the test flash ipsilateral (or contralateral) to the preceding stimulus was presented, light adaptation or forward masking is not a likely explanation for the VM. The VM probably reflects binocular interactions underlying binocular rivalry and the present results suggest that the nature of the interactions changes with temporal parameters. The VM in the flash-suppression paradigm may provide a good tool to explore how eye and stimulus rivalries occur depending upon stimulus parameters.