Determinants of visual awareness following interruptions during rivalry

The inability of the human visual system to fuse dissimilar patterns in corresponding regions of the two eyes results in stochastic alternation of perceptual dominance between the two patterns: rivalry. When rivalrous stimuli are presented intermittently their perception is stabilized (Leopold, Wilke, Maier, & Logothetis, 2002). This stability indicates the operation of some kind of perceptual memory across interruptions in stimulation. Here we examined the contents of this perceptual memory to quantify the relative contributions of different sources of information: eye-of-origin, orientation, and color. Stimuli were intermittently presented and, during each blank interruption, we swapped either the color, orientation, or eye of presentation of the gratings. Comparing the percepts reported before and after each interruption allowed us to establish what aspects of perception remained stable. During conventional binocular rivalry, the eye in which the stimulus was presented remained stable across 74% of interruptions. Stimulus color and orientation also had weaker significant effects. When eye-of-origin information was eliminated by alternating the patterns rapidly between the two eyes, stimulus color remained stable across 86% of interruptions. Stimulus orientation again had a weaker but significant effect. These results demonstrate that the mechanisms mediating perceptual stability across interruptions in rivalry can operate at both monocular and binocular levels, much like the mechanisms operating during continuous viewing of rivalrous stimuli. On the basis of this similarity, we speculate that perceptual memory across interruptions in rivalry may involve the same neural representations as visual competition during rivalry. If this is the case, the use of intermittent stimulation in rivalry might permit the investigation of aspects of the mechanisms underlying visual competition that remain hidden during continuous presentation.