Perceptual deadtime: Is there processing latency in the perceptual system

The deadtime effect is a perceptual phenomenon observed in visual search tasks in which target stimuli may be delayed up to 50 milliseconds with no apparent effect on the determination of target identity as measured by choice reaction times. Several experiments evaluated the hypothesis that the processing of critical stimuli within a visual search task can be delayed without apparent decrement in reaction time responses. This phenomenon has been labelled "perceptual deadtime" implying that there is a short period of time used by the perceptual system prior to its being able to differentially evaluate visual information. This study attempted to specify the conditions needed to produce reaction time functions that did not change in spite of delaying the critical target stimulation up to 100 milliseconds of stimulus onset asynchrony.Results showed that critical visual information could be delayed about 50 milliseconds if a precue stimulus located the subsequent target stimulus location early in the stimulus stream and if any distractor stimuli used were presented continuously throughout the duration of the search task. Displays with fewer distractors were less likely to provide reliable deadtime effects as were displays with no early location precues. These results argued that the two parameters critical to deadtime effects were the timing of precues and the pattern of distractor stimuli. The requirement of both parameters to be simultaneously present suggested an attentional process that either has two discrete stages, one stage being a global analysis of the display, followed by second stage of processing at a more localized subset of the visual display or a visual process that starts globally and becomes increasingly localized in a more continuous fashion.U of I OnlyETDs are only available to UIUC Users without author permissio