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David E. Irwin, Laura E. Thomas; Cognitive saccadic suppression: number comparison is suppressed during leftward saccades. Journal of Vision 2005;5(8):104. doi: 10.1167/5.8.104.
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It is well known that visual sensitivity is reduced during saccadic eye movements (i.e., saccadic suppression). Recent research has shown that saccades suppress some cognitive processes as well. For example, Irwin and Brockmole (2004, Psych Science) reported that saccadic eye movements interfere with dorsal-stream tasks such as judgments of object orientation but not with ventral-stream tasks such as object recognition. Because saccade programming and execution also rely on the dorsal stream, Irwin and Brockmole hypothesized that cognitive saccadic suppression might occur as a result of dual-task interference.
Judging whether one number is larger or smaller than another is a dorsal-stream task that relies especially on the right parietal cortex (Dehaene, 2003, Cognitive Neuropsychology). In the current experiment, subjects judged whether a two-digit number was greater than or less than 65 while making no, short, or long saccades. RT to make this judgment increased with saccade distance, but only when the eyes moved from right to left. Saccade velocity decreased under these same conditions, suggesting that not only did saccades interfere with cognitive processing, but cognitive processing interfered with saccade execution as well. Because the right parietal cortex is instrumental in generating leftward saccades, these results provide further support for the hypothesis that cognitive suppression during saccades occurs as a result of dual-task interference within the dorsal stream.
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