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Narcisse P. Bichot, Andrew F. Rossi, Leslie G. Ungerleider, Robert Desimone, Jeffrey D. Schall; Neuronal mechanisms of priming during popout visual search. Journal of Vision 2002;2(7):728. doi: 10.1167/2.7.728.
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Even during a simple popout search task, monkeys like humans are affected by trial-to-trial changes in stimulus features, as well as changes in target location. We investigated the neuronal mechanisms underlying such sequential effects, generally referred to as perceptual priming.
We recorded from neurons in the frontal eye field (FEF) of monkeys performing a popout search. As in previous studies, it was found that the repetition of stimulus properties improved performance. This feature-based facilitation of return was reflected in the neuronal discrimination process in FEF. Neurons discriminated the target from distractors increasingly earlier and increasingly better as the number of trials with the same stimulus features increased, reflecting improvements in saccade latencies and accuracy, respectively. The neuronal correlates of priming of popout were mediated by both target enhancement and distractor suppression. In contrast to the feature repetition effect, we found that the repetition of target position increased the latency of saccades to the target, but did not affect accuracy. This location-based inhibition of return was also reflected in the neuronal discrimination process in FEF.
Although changes in behavioral performance associated with priming of popout are reflected in the neuronal selection in FEF, we found that top-down feedback from the prefrontal cortex was not necessary for the expression of this effect. Target selection ability was tested in monkeys with unilateral prefrontal lesions. Orientation discrimination thresholds were measured for a target grating that differed from surrounding distractor gratings in color. Orientation thresholds increased with increased frequency of target and/or distractor color change (especially in the case where colors changed on every trial), but performance in the hemifield contralateral to the lesion was not differentially affected by the frequency of color change relative to performance in the control hemifield.
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