A key goal of consciousness science is identifying neural signatures of being aware vs. unaware of simple stimuli. This is often investigated in the context of near-threshold detection, with reports of stimulus awareness being linked to heightened activation in a frontoparietal network. However, due to the fact that reports of stimulus presence are also associated with higher confidence than reports of stimulus absence, these results could be explained by frontoparietal regions encoding stimulus visibility, decision confidence or both. Consistent with this view, previously we showed that prefrontal regions encode confidence in decisions about target presence (Mazor, Friston & Fleming, 2020). Here, we further ask if prefrontal cortex also encodes information about stimulus visibility over and above confidence. We first show that, whereas stimulus identity was best decoded from the visual cortex, stimulus visibility (presence vs. absence) was best decoded from prefrontal regions. To control for effects of confidence, we then selectively sampled trials prior to decoding to equalize the confidence distributions between absence and presence responses. This analysis revealed that posterior medial frontal cortex encoded stimulus visibility over and above decision confidence. We interpret our findings as providing support for a representation of stimulus visibility in specific higher-order cortical circuits, one that is dissociable from representations of both decision confidence and stimulus identity.
Neural correlates of habituation and dark adaptation in the visual cortex of the rat