Perception of temporal order in adjacent visual stimuli

Abstract For single short exposures, the temporal order of appearance of two adjacent stimuli in the human fovea can be correctly identified when one is delayed by as little as 3 msec. The threshold delay is almost unaffected by the length of the stimuli or their relative orientation, but depends critically on their separation, being minimal in the range 2–6′. Illusion of movement is strong but not a necessary condition for detection of temporal order. In the conditions showing lowest thresholds, sensitivity is less with dichoptic viewing. Uniocular stimuli in opposite directions can be combined to yield a stereoscopic appearance. If the neural processing for such fine temporo-spatial comparisons does not occur in the retina, our results imply that retino-cortical transmission of the involved signals is exceedingly crisp and that cortical processing is more delicate if stimuli arise wholly in one eye.