Neural synergy in visual grouping: when good continuation meets common fate

A modified version of the 'path finder' display consisting of many small oriented Gabor patches was used to study the joint contributions of spatial and temporal structures to shape perception. A two-interval forced-choice procedure measured detectability of curved 'paths' defined by orientation ('good continuation') and/or by temporal synchrony of change in motion direction ('common fate'). When orientation was completely random (no spatial 'path' cue) temporal synchrony still supported reliable performance, but only when correlation of change among 'path' elements was high. When combined, these two weak spatial and temporal structures yielded performance in excess of probability summation: 'paths' weakly defined by orientation were highly conspicuous when the constituent Gabors underwent synchronized changes in direction of motion, even though the individual directions of path elements were uncorrelated. Spatial grouping from temporal structure may arise from correlated transients associated with synchronized changes in motion direction. Evidently these two mechanisms for promotion of spatial grouping interact synergistically.