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Girish Kumar, Scott Stevenson; Peri-saccadic temporal uncertainty. Journal of Vision 2007;7(9):381. doi: https://doi.org/10.1167/7.9.381.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To quantify the ability of humans to localize the timing of events relative to the execution of a saccadic eye movement.
Methods: Three subjects participated in this study. Their task was to make a judgment of when a vertical grating, shifted phase by 90 degrees relative in time to a 10 degree vertical movement. The vertical movement was achieved by three methods - vertical saccades, simulated saccades and simulated saccades that were triggered by the subject with a key press. All simulated saccades were produced by moving a mirror mounted onto a galvo-motor. In all three procedures subjects had three response options - “before”, “during” or “after” the real/simulated saccade. To quantify the uncertainty in making these judgments, the spread of the time difference between the phase shift and the real/simulated saccade for “during” responses as well as the slope of the psychometric function of proportion of “after” responses were calculated.
Results: All subjects made errors in judging the temporal relationship between stimulus shift and image motion, with the largest errors occurring for the triggered task and the smallest errors in the simulated task. The average standard deviations of “during” judgments were 59.65, 28.26 and 83.81 msecs for the saccadic task, simulated saccade task and the triggered task, respectively. The mean standard deviations for discriminating “before” vs. “after” were 176.98, 128.79, and 219.76 msecs, respectively, for the three tasks.
Conclusions: Previous work has showed that subjects spatially mislocalize targets that are presented around the time of a saccade. A possible confound is that subjects misjudged when their eyes moved, relative to the target presentation. Our study shows that do make relative temporal judgment errors around the execution of a saccade, and this may largely be due to task demands of having to make a movement while making the judgment.
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