Abstract
Activity in early visual areas has been considered to be veridical whereas later visual areas, as well as regions in temporal, parietal, and prefrontal cortex, have been suggested to reflect our conscious perceptual experiences. In the present study, we assessed neural responses in early human visual cortex to physically identical stimuli with different perceptual outcomes. Intracranial electrocorticography (ECoG) was recorded from 9 patients while they performed a backwards metacontrast masking task. On each trial, the patients reported whether or not they saw a briefly presented target disk that was subsequently masked by an annulus. To compare differences in neural activity to physically identical stimuli with different perceptual experiences, we conducted a time-frequency analysis on the seen and unseen target-present trials. The power of high-gamma band oscillations in visual cortex was significantly higher between 100 and 150 ms after target onset when subjects successfully detected the target than when they missed it. Importantly, this latency window reflects activity evoked only by the target stimulus and not the subsequent mask. Other frequency bands showed no differences in post-stimulus power between the consciously perceived vs. the undetected trials. The present study shows that the power of post-stimulus high-gamma band activity in early human visual cortex reflects subjective perception. These findings suggest that activity at an early stage of post-stimulus processing in early visual cortex already reflects our perceptual experiences and call into question whether later post-stimulus activity and higher-order brain regions are necessary for visual awareness.