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Paige Scalf, Elexa ST. JOHN-SAALTINK, Markus Barth, Hakwan Lau, Floris De Lange; Time-resolved fMRI tracks attention through the visual field. Journal of Vision 2016;16(12):907. doi: 10.1167/16.12.907.
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When multiple items must be monitored, does top-down attention act on their extrastriate representations in a parallel manner or in a serial manner? Synchronous neural activity during visual search by monkeys suggests that potential target items are enhanced in parallel (Bichot et al., 2005). Rhythmic presentation of spatially disjoint targets at optimal frequencies improves their detection by humans, however, suggesting that covert attention may in fact be rapidly cycled among attended locations (e.g Van Rullen et al., 2007). Here, we use highly time-resolved fMRI (TR =~90ms ms) to directly investigate the relative time at which top-down attention modulates individual extrastriate representations. In experiment one, we measured extrastriate signal evoked by stimuli in the four quadrants under three conditions. A simultaneous, 400 ms, 25% increase in luminance of all four items served as a model for simultaneously distributed attention. A sequential 100 ms, 100% increase in luminance for each item served as a model for sequentially allocated attention. We compared these with an attended condition, in which participants monitored the four items (whose luminance did not change). The onset and peak of the evoked BOLD response in corresponding extrastriate regions did not change significantly for simultaneous stimulation conditions (p >.3). Repeated-measures ANOVA revealed the difference between peak and onsets were significantly greater for the sequential (p < .04) and attended (p< .05) than for the simultaneous presentation condition. In a second experiment, reversing the order of sequential stimulation also reversed the order in which BOLD signal onset and peaked in visual cortex (p < .05). These data show that highly time-resolved fMRI can reveal difference in the time-course of signal across brain regions. Top-down attention acts across multiple extrastriate representations in serial.
Meeting abstract presented at VSS 2016
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