On the mechanisms of feature expectation and feature-based attention in the primary visual cortex

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Both feature-based attention and feature expectation facilitate perception about the world around us. Whereas feature-based attention is known to act globally and spread across the visual field, the mechanisms of feature expectation are largely unknown. Using fMRI and visual grating stimuli, we investigated whether the effects of feature expectation are also global, or act in a more retinotopically specific way. We did so by investigating the expectation effects in different parts of the visual cortex (V1). The BOLD response contralateral to expected stimuli was reduced compared to unexpected stimuli. This effect did not spread across the visual field – in fact, in ipsilateral V1, the BOLD response was increased when an expected stimulus was presented compared to when an unexpected stimulus was presented. For the non-cued grating, the orientation of which was orthogonal to the expectation cue, no effects were found as a result of whether this unattended grating was congruent or incongruent with the expectation the participants had about the cued grating. These findings suggest that the mechanisms of feature expectation are retinotopically specific. Additional orientation specific BOLD analyses suggested that feature-based attention, on the other hand, spreads across the visual field. These findings would be in line with the idea of separate neuronal mechanisms for attention and expectation.
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