Multiple Visual Latency

Abstract

It has long been known that the time taken to detect a dim visual stimulus is longer than that to detect a bright one, with a relative delay of up to several tens of milliseconds. Systematic studies of various phenomena demonstrating this delay have revealed that the perceptual latency decreases monotonically as the stimulus intensity increases. Because latencies measured by psychological methods and cortical evoked responses are very similar to electroretinogram latencies, it has become a common belief that there is little in the intensity-dependent latency function that cannot be explained by retinal processes. We report evidence that there is not one absolute visual delay common to the whole visual system, but that the delay varies considerably in different perceptual subsystems. The relative visual latency was found to be considerably shorter in a movement-discrimination task than in other perceptual tasks which presume visual awareness of the onset of visual events, or of their temporal order.