Spatial Structure Affects Temporal Judgments: Evidence for a Synchrony Binding Code

Visual binding is the process by which the brain groups the elements belonging to one object, whilst segregating them from other scene elements. A computationally parsimonious mechanism of visual binding is the binding-by-synchrony (BBS) hypothesis. According to this hypothesis, detectors that respond to elements of a single object fire in synchrony, while detectors that respond to elements of different objects do not. Current psychophysical and physiological evidence are inconclusive about the role of BBS in the visual integration process. Here we provide psychophysical and computational evidence suggesting that the visual system implements a mechanism that synchronizes response onsets to object parts and attenuates or cancels their latency differences. In three experiments, observers had to judge the synchrony of two flickering Gabor patches embedded in a static Gabor contour, passing through fixation. We found that a smooth contour, as compared to a jagged one, impedes judgments of temporal synchrony between the targets, whilst facilitating non-temporal judgments of contrast on the same targets. We show that the results are consistent with a simple computational model that implements synchronization of responses via lateral interactions, enabling the visual system to pick up objects by synchrony among a temporally diverse background.