Abstract
What are the neural correlates of perceptual awareness? To answer this question, numerous studies have examined the differences in neural activity elicited by visible and invisible stimuli. In virtually all of these studies, observers are asked to report the contents of their experience to objectively confirm that they perceived the critical stimulus (e.g., “I saw an object”). When a stimulus is not perceived, however, observers can only provide a random guess. Therefore, it is not clear if the neural responses evoked by a perceived stimulus are associated with conscious perception or with post-perceptual processes involved in reporting that stimulus (e.g., remembering the target, planning a response, etc.). To separate neural correlates of awareness from neural correlates of post-perceptual processing, we used a novel no-report visual masking paradigm while participants were scanned using fMRI. In the report condition, participants indicated whether or not they saw each stimulus. In the no-report condition, they did not make such reports. With univariate analyses, we replicated prior results in the report condition showing that visible stimuli elicit widespread activation across the ventral pathway and fronto-parietal regions. In the no-report condition, the amount of activation in fronto-parietal regions dropped significantly relative to the report condition. However, although this fronto-parietal activation was severely attenuated in the no-report condition, there was still significantly more activation for visible than invisible stimuli in these regions. Similarly, using multivariate analyses, we found a significant drop in decoding of target visibility in the no-report compared to the report condition, but decoding accuracy still remained significantly above-chance in fronto-parietal regions. Together, these results highlight the importance of distinguishing perceptual awareness from post-perceptual processes and suggest that a smaller, more circumscribed subset of the fronto-parietal network may play a crucial role in conscious awareness even after minimizing the influence of these post-perceptual processes.