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Ian C. Fiebelkorn; Rhythmic sampling at both cued and uncued locations. Journal of Vision 2015;15(12):1399. doi: 10.1167/15.12.1399.
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© 2017 Association for Research in Vision and Ophthalmology.
The brain directs its limited processing resources through various selection mechanisms, broadly referred to as attention. Spatial selection, one such mechanism, is sometimes likened to a spotlight, continuously highlighting regions of the visual scene for preferential processing. Evidence suggests that the operation of this spotlight is linked, at least in part, to neural oscillations. In fact, rhythmic fluctuations attributable to spatial selection have been directly observed in behavior. When spatial selection is fixed at a single target location, visual-target detection oscillates at 8 Hz. When spatial selection is split between two equally likely target locations, visual-target detection at each location instead oscillates at 4 Hz, with peaks in detection alternating between the two locations. Landau and Fries (2012) proposed that these oscillatory patterns at 8 and 4 Hz are attributable to the same neural source, either sampling a single location or alternately sampling two locations. We recently observed both patterns during an experimental task that utilized three potential target locations. A cue (80% valid) indicated the location where a visual target was most likely to occur. As predicted, visual-target detection at the cued location oscillated at 8 Hz, suggesting that participants successfully deployed spatial selection. Yet visual-target detection at each of two uncued locations oscillated at 4 Hz, with peaks in detection alternating between the uncued locations. I will argue that these behavioral data, rather than reflecting a single neural source, support the existence of two attentional spotlights that concurrently sample the visual scene: one fixed spotlight that samples the most relevant location, and a second moving spotlight that rhythmically monitors less relevant locations. We have now replicated these behavioral findings in two monkeys, demonstrating that rhythmic sampling is consistent across primate species. We will next use electrophysiological recordings to investigate the neural sources underlying these behavioral oscillations.
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