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Fabrice Arcizet, Koorosh Mirpour, Weisong Ong, James Bisley; Encoding a salient stimulus in the lateral intraparietal area (LIP) during a passive fixation task. Journal of Vision 2010;10(7):910. doi: 10.1167/10.7.910.
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© ARVO (1962-2015); The Authors (2016-present)
When exploring a visual scene, some objects preferentially grab our attention because of their intrinsic properties. In this study, we examined the responses of neurons in LIP to salient stimuli while naive animals performed a passive fixation task. We defined the salient stimulus as a color popout among stimuli of another color; either red or green. The animals started a trial by fixating a central spot after which a circular array of 6 stimuli was flashed for 750 ms. The array was arranged so that only one of the stimuli was in the receptive field (RF). The animals had to keep fixation to be rewarded. We used 4 different conditions: the field condition, in which all the stimuli had the same color; the distractor condition, in which the salient stimulus was presented outside the receptive field, so a distractor was inside the RF; the popout condition, in which the salient stimulus was inside the RF; and the singleton condition, in which only a single stimulus was presented inside the RF. We recorded from 42 LIP neurons and found that the mean response to a salient stimulus was significantly higher than the mean response to a distractor, but significantly lower than the mean response to a singleton. The time at which the popout activity rose above the distractor activity was relatively early suggesting that bottom-up information from early visual areas converges at LIP. Interestingly, there was a tight correlation in response to the popouts and distractors of similar colors, suggesting gain control. We also found that some LIP neurons prefer a particular color, but these neurons still had elevated responses to a popout compared to a distractor, consistent with the presence of gain control. Together these results indicate that LIP highlights salient stimuli even when they are task irrelevant.
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