Abstract
Past fMRI studies have shown that lateralized visual stimuli evoke a neuronal pattern across primary visual cortex that resembles a Mexican hat, where positive activation in the center is flanked by negative activation (deactivation) in the surround. We examined (1) how visual spatial attention modulated the Mexican hat activation profile, and (2) whether attended information is better encoded in the enhanced center or the suppressed surround. The participant was cued in the beginning of each trial to deploy covert attention to the left or the right visual field. Following a random time delay, a vertical grating was presented in one of the two visual fields, and the participant was asked to discriminate the frequency of the grating (low vs high) in the attended visual field and ignore the grating in the unattended visual field. Analyzing the fMRI data recorded from the experiment, we found that relative to the unattended stimulus, the attended stimulus evoked both stronger center activation and stronger surround deactivation. Applying MVPA analysis to decode high versus low spatial frequencies of the attended stimulus, we found that while the decoding accuracy is above chance in both the activated center and the deactivated surround, it is higher in the activated center than the deactivated surround. These results suggest that visual spatial attention both enhances and suppresses neural activity in the visual cortex by accentuating the Mexican hat response profile such that attended information is more efficiently represented in the activated center than the deactivated surround.