Pre-adaptation effects in multistable binocular rivalry

We recently reported path dependence and on-line adaptation in multistable binocular rivalry (Suzuki & Grabowecky, 2002, Neuron, 36, 143-157). Perceptual transitions between a pair of related shapes (e.g., opponent convex and concave shapes) were elevated, termed " perceptual trapping." During such trapping, on-line adaptation to perceived shapes increased the probability to break from trapping and to shift to an unrelated shape. Here we examined effects of pre-adaptation in multistable binocular rivalry. As before, rivalry displays were quadra-stable, generating 2 pairs of opponent shapes (e.g., diamond and hourglass [convexity opponent] and right- and left-pointed chevrons [curvature opponent]). Observers pre-adapted to one of the 4 shapes. Adaptors were binocular, low contrast (compared to the rivalry stimuli), and contrast-polarity reversed (1.9 Hz) to prevent afterimages. In each trial, an adaptor (30 s) was followed by a rivalry inspection period (20 s) during which observers continuously reported dominant shapes. Transition probabilities to and dominance durations of adapted shapes were reduced relative to no-adaptation control conditions. Interestingly, adaptation to a shape also boosted its opponent shape in some cases (both in transition probability and dominance duration). These results cannot be explained solely in terms of low-level contour adaptation because similar effects occurred (though reduced in magnitude) with small adaptors (25% in area relative to rivalry stimuli). Further, we found evidence that perceptual transitions can be primed. For example, when diamond and hourglass shapes were alternated (0.6 Hz) during adaptation, the transitions between them were increased during rivalry. Thus, in multistable binocular rivalry, pre-adaptation weakens adapted shapes, can strengthen opponent shapes, and can prime specific perceptual transitions.