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David Bridwell, Elizabeth Hecker, Ramesh Srinivasan; Different attentional strategies are reflected by modulations in the feature tuned flicker response. Journal of Vision 2011;11(11):132. doi: https://doi.org/10.1167/11.11.132.
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Attentional modulations in early sensory areas (such as striate and extrastriate cortex) arise in part from activity within parietal locations involved in attentional control. However, the influence of attention on parietal responses to unattended stimuli is relatively unexplored. We measured parietal SSVEP responses to an unattended left visual field flickering grating (F2 = 8 or 12 Hz) while individuals (n = 11) attended to orientations that were offset by 0, 10, 20, 30, 40 and 90 degrees from the orientation of the unattended flicker. These attentional tuning curves were measured during Detection, Fine Discrimination, or Coarse Discrimination of Gabor's. Differences in attentional strategies encouraged by each task may be reflected by differences in the attentional tuning curves. We found that during Detection there is a monotonic decline in the SSVEP response to the unattended 8 Hz flicker as the attended orientation is shifted 0, 10, 20, and 30 degree offset from the flicker orientation. This monotonic decline is not present when individual's discriminate the target from an orthogonal target (Coarse Discrimination). The monotonic decline is present during Fine Discrimination with a broader fall-off compared to Detection. Few attentional modulations were observed with a 12 Hz flicker. These differences in the 8 Hz attentional tuning curves likely reflect the degree in which attentional gain is applied over a range of orientations during each task. During Detection individuals appear to apply the sharpest gain on the attended orientation. When discriminating between another Gabor oriented 90 degrees away (Coarse Discrimination) attentional gain is flattened. Finally, attentional tuning during Fine Discrimination is intermediate, resulting from either a broadening of attentional gain or an increased gain applied to orientations that are off-center from the two potential targets. Thus, parietal SSVEP responses to an unattended flickering grating (8 Hz) are modulated by attended orientation, and are sensitive to attentional strategies.
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