Neural Sharpening of Object Categories Through Parafoveal Priming

During natural vision, humans make saccades approximately every 250 - 300 ms to fixate on important objects in a scene. Given this rapid succession of eye movements, it has been proposed that visual processing begins in the parafovea, prior to fixation. Such parafoveal previewing may serve as a form of priming, facilitating subsequent processing at fixation. In this study, we investigated whether parafoveal priming leads to both a reduced neural response - akin to repetition suppression - and a more selective neural representation, consistent with neuronal sharpening. Participants performed a visual exploration task involving natural object images that were either parafoveally previewed or not, while magnetoencephalographic (MEG) data were recorded. Event-related fields revealed a reduced neural response when an image had been parafoveally presented 250 ms earlier. Moreover, multivariate pattern analysis showed enhanced decoding of object category following parafoveal priming, suggesting increased neural specificity. These findings support the idea that parafoveal previewing contributes to neural sharpening, potentially aiding evidence accumulation by forming sparse and precise representations of objects during visual scene exploration.