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Frank E. Visco, Scott B. Stevenson, Harold E. Bedell; Saccades alter perceived duration of full field decrement flashes. Journal of Vision 2001;1(3):223. doi: 10.1167/1.3.223.
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© ARVO (1962-2015); The Authors (2016-present)
PURPOSE: Previous psychophysical experiments have shown that targets presented around the time of a saccade are often mislocalized in space. In this experiment we ask whether a decrement flash presented around the time of a saccade is misjudged with respect to its temporal duration. METHODS: Subjects viewed a white screen with two black plus signs separated by 20 degrees with the left eye. A small diffusing hemisphere presented a 28Cd/m2 ganzfeld to the right eye. EOG electrodes were placed on both temples. On each trial, a standard 100ms decrement flash was presented while the subject fixated on the left cross. The subject then made a saccade to the right cross, which triggered a comparison decrement with a duration of 40, 60, 80, 100, 120, 140, or 160ms. Subjects indicated whether the comparison was longer or shorter than the standard. A block of trials consisted of 25 repetitions of each of the seven comparisons. The resulting psychometric function (% “longer” vs. comparison duration) was analyzed to determine the Point of Subjective Equality (PSE). In separate blocks, comparison flashes were triggered at 0ms, 25ms, 50ms, 75ms, or 125 ms delay after saccade onset. Results were compared to a no-saccade control condition. RESULTS: All subjects showed a shift of the PSE around the time of the saccade, such that the comparison flash had to be longer in order to appear equal to the standard. Across all subjects the average shift in the PSE was about 15ms at zero delay, with progressively smaller shifts for longer delays. CONCLUSION: Saccadic eye movements interfere with our ability to accurately judge the temporal duration of a full-field decrement flash. Such temporal misjudgments can play a role in the reported spatial mislocalization of a target presented during a saccade. It remains unclear whether the apparent decrease in perceived duration is caused by a change in temporal processing or by the attenuation of signals due to a saccadic suppression mechanism.
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