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Ilona Bloem, Sam Ling; Attentional gain modulation relies on local feature-tuned normalization.. Journal of Vision 2016;16(12):602. doi: 10.1167/16.12.602.
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© ARVO (1962-2015); The Authors (2016-present)
Attentional feedback has been shown to evoke increases in the gain of early visuocortical responses, but its effects are rather heterogeneous, even within a visual area. What neural computations give rise to these gain changes? Here, we used fMRI to investigate the hypothesis that gain increases with attention rely on normalization. Specifically, we examined whether visuocortical responses that exhibit stronger weighted feature-tuned normalization would also exhibit larger attentional benefits. To do so, we measured the local, voxel-wise magnitude of both orientation-tuned normalization and attentional modulation within early visual cortex. We assessed normalization strength by presenting participants with stimuli composed of two oriented gratings, which were combined in either a collinear or orthogonal configuration. Collinear stimuli evoked weaker mean BOLD responses than orthogonal stimuli, indicating substantial tuned normalization in early visual areas. Furthermore, the magnitude of local normalization strength varied substantially between voxels within a visual area, indicating heterogeneity across a population. We next explored how local normalization strength correlates to the magnitude of attentional modulation. Attentional modulation was measured in the same participants by presenting oriented stimuli, which participants either covertly attended towards (performing a fine orientation discrimination task), or attended away from (performing a demanding task at fixation). We found an overall increase in BOLD response when attention was directed towards a stimulus. Voxel-wise analyses illustrated substantial variability in the amount with which attention boosted stimulus-evoked responses. Leveraging the population-wide heterogeneity in both measures, we discovered a strong association between normalization strength and the strength of attentional modulation. Taken together, our results reveal a link between attentional gain and normalization, suggesting that these two measures potentially share a common mechanism, allowing attention to improve perceptual discriminability by modulating local circuitry in early visual cortex.
Meeting abstract presented at VSS 2016
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