Abstract
Correlated change in a dynamic visual property (e.g., motion) among a subset of stimulus elements promotes spatial grouping of those elements within a background of dynamic elements whose changes are uncorrelated in time [Lee & Blake (1999) Science, 284, 1165] What is the minimum time needed for perception of spatial structure created from this kind of temporal structure? To learn the answer, we created animation sequences in which hundreds of small, radial gratings changed their directions of rotation randomly over time. A “figure” region defined solely by correlated change in rotation direction “moved” laterally left or right (a novel form of higher-order motion). Speed of motion was varied to find the value supporting reliable direction discrimination performance on a 2AFC task. The task could be performed at exposure durations as brief as 42 msec, with performance reaching perfection at durations just over 100 msec. In the blink of an eye, human vision can dynamically organize spatial structure from fine temporal structure and exploit that structure to compute higher-order motion.
In a related experiment, contours within many small, randomly oriented Gabor patches changed their directions of motion irregularly over time, with the change times for all Gabors dictated by the same point-process. Over trials, the temporal phase-lag between “figure” and “background” point-process was manipulated, to find the minimum phase-lag supporting accurate shape discrimination. Consistent with earlier findings, shape from temporal phase-lag could be perceived when figure and ground elements differed in their change times by less than 10 msec. Simulations confirmed that these results are not predicted by low-pass temporal filtering [Adelson & Farid (1999) Science, 286, 2231]. These results serve as testimony to human vision's exquisite sensitivity to temporal structure.
NIH EY07760