Multiple visual latency

It has long been known that a dark visual stimulus is seen later than a bri ght one, with a delay up to several 10s of milliseconds. Systematic studies of various phenomena demonstrating this delay have revealed that the perce ptual latency decreases monotonically as the stimulus intensity increases. Because latencies measured by psychological methods and cortical evoked res ponses are very similar to electroretinogram latencies, it has become a com mon belief that there is little in the intensity-dependent latency function that cannot be explained by retinal processes. In this study, we report ev idence that there is no one absolute visual delay common to the whole visua l system but rather that the delay varies considerably in different percept ual subsystems. The relative visual latency was found to be considerably sh orter in the task involving detecting the direction of movement than in oth er perceptual tasks that presume visual awareness of the beginning or tempo ral order of visual events.