Dynamic bistable Gestalt perception enhances and reduces activity in early visual cortex in retinotopically predicted areas

A growing body of literature suggests that feedback modulation of early visual processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content have been shown to suppress early visual regions, typically interpreted in the framework of predictive coding. However, physical stimulus differences can preclude clear interpretations in terms of feedback. Here we examined activity modulation in V1 and V2 during distinct perceptual states associated to the same physical input. This ensures in a unique way that observed signal modulations cannot be accounted for by changes in physical stimulus properties, and can therefore only be accounted for by percept-related feedback interactions from higher level regions. We used a dynamic stimulus consisting of moving dots that could either be perceived as corners of a large moving square (global Gestalt) or as distributed sets of locally moving dots. We found that perceptual binding of local moving elements into an illusory Gestalt led to spatially segregated differential modulations, in both, V1 and V2: representations of illusory lines and foreground were enhanced, while inducers and background suppressed. The results extend prior findings to the illusory-perceptual state of physically un-changed stimuli, and for the first time show background suppression in the human brain. Based on prior work, we hypothesize that parietal cortex is responsible for the modulations through recurrent connections in a predictive coding account of visual processing