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Chin-An Wang, Susan Boehnke, Douglas Munoz; Pupil dilation evoked by a salient auditory stimulus facilitates saccade reaction times to a visual stimulus.. Journal of Vision 2012;12(9):1254. doi: 10.1167/12.9.1254.
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The orienting reflex is initiated by a salient stimulus to prepare the body for quick, appropriate action. It involves a rapid shift of the eyes, attention, and other physiological responses, including pupil dynamics. The superior colliculus (SC) is a critical structure in the brain network that coordinates orienting behaviors, and we have previously shown that microstimulation of the SC in monkeys not only shifts in gaze and attention but also evokes pupil dilation. Although pupil dilation is characterized as an important component of the orienting reflex, its functional role remains poorly understood. It has been hypothesized to increase visual sensitivity. We first used a salient infrequent auditory stimulus to evoke pupil dilation. An auditory tone at zero azimuth (1000 Hz, 50 ms) was presented on only 20% of trials while monkeys fixated a central point. The pupils dilated transiently after the auditory stimulus presentation with dilation onset about 200 ms and dilation peak about 500 ms after stimulus onset, confirming that pupil dilation was triggered by auditory stimuli. Then, we presented a visual saccadic target after the auditory cue to examine the effect of evoked pupil dilation on saccadic reaction times. Critically, we manipulated the cue-target onset asynchrony (CTOA: 100-850 ms) according to the time course of evoked pupil dilation, so the size of the pupil varied at different times of target presentation. Pupils dilated maximally when the CTOA was 400 ms, the condition for which the evoked pupil size was maximal during target presentation. Moreover, saccade reaction times were negatively correlated with actual pupil size (faster reaction times occurred with a larger pupil), suggesting that pupil size influences ongoing target processing. Together, these results suggest that pupil dynamics are associated with saliency, and that stimulus-evoked pupil dilation may facilitate target processing for action.
Meeting abstract presented at VSS 2012
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