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Robert M. McPeek; Superior colliculus activity related to reflexive and top-down shifts of attention. Journal of Vision 2007;7(9):343. doi: 10.1167/7.9.343.
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Saccades and covert shifts of attention are used to improve perception of peripheral stimuli. The primate superior colliculus (SC) plays a central role in saccades, and recent evidence suggests its involvement in visuo-spatial attention. To test the role of the SC in attention, we recorded single-unit activity as monkeys remained fixated and discriminated the orientation of a briefly-presented peripheral target embedded in an array of distractors. The target could appear in one of six isoeccentric locations, and distractors appeared in the other locations. In some blocks of trials, attention was reflexively cued to the target location by a color-oddity cue that preceded the target. In other blocks, top-down control of attention was tested by making the target more likely to appear in one location than in the others. Both the reflexive and top-down manipulations had significant effects on the accuracy of discriminating the target's orientation, indicating that they influenced attention. Activity in a subpopulation of visually-responsive SC cells was strongly modulated by reflexive precues, showing a sustained increase in activity when attention was cued into their receptive fields. This attention-related activity continued until the onset of the discrimination target. In contrast, none of the SC cells was modulated by the top-down attention manipulation. These results indicate that during fixation, SC activity is correlated with the locus of reflexively-cued attention, and suggest that the SC is involved in controlling reflexive shifts of attention, but not in controlling top-down shifts of attention.
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