The role of spatial interactions in perceptual synchrony.

To understand how the visual system processes synchronies between visual patterns, we investigated the temporal acuity for detecting a Gabor pattern whose orientation was alternated (vertical-horizontal) in a different temporal phase from three other Gabor patterns. Thresholds of both advanced and lagged temporal-phase offsets were measured for various temporal frequencies of orientation alternation and for various spatial distances between Gabor patterns. The thresholds for advanced phase offsets were lower than those for lagged phase offsets; the target pattern whose orientation changed earlier than the others was easier to detect than the target whose orientation changed later by the same amount. It was found that the amount of this temporal asymmetry increased proportionally with the distance between patterns. The upper temporal-frequency limit of orientation alternation for detecting the target pattern also systematically decreased with the distance between patterns. These results were interpreted as reflecting the temporal dynamics of mutual interactions between local orientation detectors, which necessarily involve a greater degree of temporal blur and longer delays of interacting signals as the spatial distance between detectors increases. This explanation leads to the notion that perceptual synchrony between visual patterns is determined in a space-time relative manner.