Integration of motion information during binocular rivalry

Abstract

When two moving gratings are superimposed in normal viewing they often combine to form a pattern that moves with a single direction of motion. Here, we investigated whether the same mechanism underlies pattern motion when drifting gratings are presented independently to the two eyes. We report that, with relatively large circular grating patches (4 deg), there are periods of monocular dominance in which one eye's orientation alone is perceived, usually moving orthogonal to the contours (component motion). But, during the transitions from one monocular view to the other, a fluid mosaic is perceived, consisting of contiguous patches, each containing contours of only one of the gratings. This entire mosaic often appears to move in a single direction (pattern motion), just as when two gratings are literally superimposed. Although this implies that motion signals from the perceptually suppressed grating continue to influence the perception of motion, an alternative possibility is that it reflects a strategy that involves integrating directional information from the contiguous single-grating patches. To test between these possibilities, we performed a second experiment with very small grating stimuli that were about the same size as the contiguous single-grating patches in the mosaic (1-deg diameter). Despite the fact that the form of only one grating was perceived, we report that pattern motion was still perceived on about one third of trials. Moreover, a decrease in the occurrence of pattern motion was apparent when the contrast and spatial frequency of the gratings were made more different from each other. This phenomenon clearly demonstrates an independent binocular interaction for form and motion.