Abstract
In common fate, elements move synchronously tend to be grouped together. However, precise temporal synchrony might not be preserved in multiple layers of processing. Thus, temporal structure, defined as the pattern of element changes over time, might play a more important role underlying common-fate processing. We compared the grouping effects of common fate under two temporal structure manipulations (same vs. different). The stimulus display contained moving random dots with the same moving speed. A total of 40% of the dots (signal dots) moved in the same direction; the others (noise dots) moved in random directions. The stimulus display could be perceived as four rows or columns based on temporal synchrony (timing difference) in changing the direction of movement between signal dots in different columns/rows. Participants were required to determine whether the stimulus was composed of rows or columns. The same structural condition was manipulated by introducing a lag between the columns/rows while different structure conditions were manipulated by introducing either a lead or a lag. Hence, the temporal structure was different but the temporal asynchrony was the same locally between the two conditions. The performance (proportion correct) under four levels of temporal frequency (TF, 2, 4, 6, 8 Hz) and various temporal asynchrony were compared. The results showed that the optimal proportion correct was modulated by the TF under different structural conditions, while it was insensitive under the same structural conditions. The asynchrony discrimination thresholds, defined as the midpoint between the low and high plateau, were not modulated by the TF under different structural conditions while decreasing as the TF increased in the same structural condition. In conclusion, the visual system used both temporal synchrony and a temporal structure to achieve the perceptual grouping underlying common fate. Additionally, with the increase of TF, the temporal structure became more effective.