Abstract
We studied spatiotemporal integration of biological motion using a summation technique. Subjects had to identify coherent from incoherent motion of a synthetic walker against a background of noise, where incoherence is produced by moving the upper and lower body in opposite directions. Performance (defined as the maximum added noise for reliable discrimination) increased steeply with exposure duration, up to very long intervals, in the order of seconds, far longer than for simple motion targets (complete by about 100 ms). Varying the speed of the walker suggested that the limiting factor for performance is the total information about the stimulus (accrued over seconds), rather than stimulus duration per se. Sampling the joints during the motion sequence (with a ‘limited lifetime’ paradigm) revealed very strong spatial summation. Sensitivity increased with the cube of the spatial information content. The spatial and temporal summation seemed to be independent of each other.
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