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Todd M. Herrington, John A. Assad; Neural activity in areas LIP and MT during rapid covert shifts of attention. Journal of Vision 2006;6(6):747. doi: 10.1167/6.6.747.
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© ARVO (1962-2015); The Authors (2016-present)
How fast can visual selective attention be shifted in the absence of eye movements? We studied primate areas LIP and MT during covert shifts of attention between visual targets, while simultaneously measuring the behavioral time course of the attentional shift.
Monkeys were trained to detect a 50-ms duration speed increase at one of two patches of coherently moving dots. A cue at the fixation point indicated which patch was more likely to change. The cue was valid on 85% of trials. Critically, on 40% of trials the cue switched at an unpredictable time to indicate that the previously uncued patch was now cued.
Detection performance at the cued patch was characterized by improved accuracy (67% vs. 37%, p << 0.0001) and decreased reaction times (462 vs. 474 ms, p << 0.0001). On switch trials, the monkey rapidly switched attention around the time of the switch cue. Surprisingly, this behavioral switch was first evident for speed changes occurring immediately before the switch cue itself, consistent with visual buffering of the target stimuli akin to iconic memory.
The responses of LIP and MT neurons were enhanced by attention. In both neural populations the attentional modulation switched at ∼200 ms after the switch cue. Comparing the neuronal attentional switch time with the visual response to the target speed change, we observed that the attentional switch was sufficiently fast to interact with a simultaneously presented speed change. This may represent a neural correlate of the behaviorally evident visual buffer.
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