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Jan Drewes, Rufin VanRullen; Ongoing EEG oscillations and saccadic latency. Journal of Vision 2010;10(7):508. doi: 10.1167/10.7.508.
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The state of the cortex at the time of a visual event can affect the way in which the event is processed. While the amplitude of ongoing oscillatory activity is known to correlate with perceptual performance, the influence of oscillatory phase remains less clear; however, it has previously been shown that the phase of ongoing activity can predict near-threshold stimulus detection (Busch, Dubois & VanRullen, J Neurosci. 2009). Here, we aim to determine the relation between the phase of ongoing oscillations in various frequency bands and the trial-to-trial variations in saccadic behavior. Human saccadic response times are known to exhibit bimodal distributions, particularly in “gap” paradigms (i.e., with a delay between fixation offset and target onset). Additionally, motor responses (manual and ocular) can exhibit certain periodicities in their latency histograms. Both of these observations may be suggestive of an underlying oscillatory influence. We employed 3 tasks, accounting for 3 different modes of saccadic behavior: 1) predictable target location, allowing for mostly reflexive and even anticipatory saccadic responses with minimal cognitive demand; 2) unpredictable target location without distractors, allowing for mostly reflexive responses with little cognitive effort, yet minimizing anticipatory responses; 3) unpredictable target location in the presence of a distractor, requiring a cognitive effort (comparison between target and distractor) before a correct saccade could be performed. Eye traces and 64-channel EEG activity were recorded simultaneously using independent, synchronized measuring equipment. The mean saccadic reaction times in the three conditions reflected the expected increase with task difficulty. In addition, the latency distributions often displayed multiple modes or periodicities. Finally, we measured the dependency of saccadic latency on ongoing (pre-stimulus) and evoked (post-stimulus) oscillations in various frequency bands, and the interaction between these periodicities and the cognitive load of the saccadic task.
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