Susanne Stoll published her first article in which she investigated how perceptual grouping of moving stimuli is represented in human visual cortex. We used a novel searchlight method for projecting brain activity back into the visual space. Essentially, we use population receptive fields measured independently via retinotopic models as encoding models to infer which parts of the visual field produce a neural response. There have been a number of studies using similar approaches. What is different about our approach is that it produces comparably clear reconstructions whilst being actually quite straightforward.
The first experiment in this study investigated a bistable illusion that can either be perceived in a local and global state, and conscious experience constantly fluctuates between these two. That allows us to disentangle the neural signature of actual perceptual grouping from the underlying physical stimulus that presumably remains constant. We replicated previous findings that early visual cortex (especially V1) shows suppressed responses to the global compared to the local state. Higher, object-sensitive regions on the other hand showed a stronger response to the global stimulus. Critically, the suppression in early visual cortex was widespread. In follow-up experiments we then found that for non-ambiguous motion stimuli designed to broadly mimic the grouping conditions of our bistable stimuli, we found suppression all over the visual cortex, including higher areas. This demonstrates that this suppression is not specifically related to perceptual grouping of local features into global objects. Moreover, the suppression is probably not universal across the cortex but is after all diffusely localised to the general location of the stimuli.
Stoll, S, Finlayson, NJ, & Schwarzkopf, DS (2020). Topographic Signatures of Global Object Perception in Human Visual Cortex. NeuroImage In press.