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Angela L. Gee, Anna E. Ipata, James W. Bisley, Michael E. Goldberg; Activity in monkey lateral intraparietal area reflects saccade direction, saccade latency, and target identification during free visual search. Journal of Vision 2005;5(8):99. doi: 10.1167/5.8.99.
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© ARVO (1962-2015); The Authors (2016-present)
Most physiological studies of saccadic eye movements and visual search reward animals for making specific eye movements, and withhold reward when they make incorrect eye movements. However, in ordinary visual behavior there is no such thing as a wrong eye movement. Instead, monkeys and humans scan the visual environment with saccades, using the eye movements to facilitate visual perception. In this study we permitted free eye movements during a visual search task, requiring the monkey to report a feature in the environment and allowing the monkey to make saccades at its own pleasure. We then examined the role of the lateral intraparietal area (LIP) in the generation of these more naturalistic saccades. The monkeys had to report the orientation of a target among an array of distractors by making a non-targeting hand movement. After the stimuli appeared, the monkeys were free to explore the array and they often made multiple saccades with their initial saccade going to a distractor. LIP activity was modulated by both the stimulus significance and the direction of the saccade. Neural activity distinguished between saccade targets and non-targets 86 ms after the array appeared, whether or not the saccade was made to the search target or to a distractor. This neural discrimination time correlated with saccade latency, suggesting that LIP could contribute to the selection of the saccade target. Neural activity in LIP also distinguished between a distractor in the receptive field and the search target in the receptive field on trials in which the first saccade went away from the receptive field. This discrimination occurred 111 ms after the array appeared, a time after the selection of the saccade target, but well before the beginning of the saccade. These data suggest that the processes of selecting a saccade goal and distinguishing the search target from distractors during visual search may run in parallel and both can be seen in LIP before a saccade.
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