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Avi Caspi, Brent R. Beutter, Miguel P. Eckstein; The time course of visual information accrual guiding eye movement decisions during visual search. Journal of Vision 2004;4(8):743. doi: 10.1167/4.8.743.
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© ARVO (1962-2015); The Authors (2016-present)
In visual search tasks, the decision of where to make a saccadic eye movement is based on visual information accumulated prior to the saccade, but about 100 ms before the saccade is initiated, new visual information cannot be used by the brain to influence that saccade's destination. Does the brain simply ignore the information presented during this brief interval immediately prior to a saccade's initiation or is this information used in making subsequent saccadic decisions? To answer this question, we applied a temporal version of reverse correlation analysis. The observers' task was to search for a bright target among 4 dim distractors, evenly spaced along a 6.4 eccentricity imaginary circle. The target and the distracros were Gaussians with full width at half maximum of 0.4 deg. The target mean luminance was 6.8 cd/m2 and that of the distractors was 4.7 cd/m2. The intensity of the target as well as the distractors was varied over time, every 25 ms, by adding samples of noise from random normal distributions, with a standard deviation of 1.5 cd/m2. Noise making a distractor brighter than the target will tend to lead observers to make an incorrect saccade to that distractor, provided that it presented during the times in which the brain gathers visual information (accrual stage). In contrast, noise presented during the times in which new visual information does not influence the saccadic decision (post-accrual stage) will not affect the saccadic decision. Results show that when a sequence of two saccades were made, the second saccade's accrual stage occurs primarily before the first saccade's initiation, including during the post-accrual stage (dead time) of the first saccade. Conclusion: Information presented immediately prior to the saccade is not used in making the immediate saccadic decision, but instead is stored and used by the neural processes driving the following saccade.
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