Visual shape completion recovers object size, shape, and position from sparsely segregated edge elements. Studies of the process have largely focused on occipital cortex, but the role of other cortical areas and their functional interconnections remains poorly understood. To reveal the functional networks, connections, and regions of shape completion across the entire cortex, we scanned (fMRI) healthy adults during rest and during a task in which they indicated whether four pac-men formed a fat or thin illusory shape (illusory condition) or whether non-shape-forming pac-men were uniformly rotated left or right (fragmented condition). Task activation differences (illusory-fragmented), resting-state functional connectivity, and multivariate pattern analyses were performed on the cortical surface using 360 predefined cortical parcels (Glasser et al., 2016) and 12 functional networks composed of such parcels (Ji et al., 2019). Brain activity flow mapping ("ActFlow") was used to evaluate the utility of resting-state connections for shape completion. Thirty-four parcels scattered across five functional networks were differentially active during shape completion. These regions were densely inter-connected during rest and a plurality occupied the secondary visual network. Posterior parietal, dorsolateral prefrontal, and orbitofrontal regions were also significant in the dorsal attention and frontoparietal networks. Functional connections from the dorsal attention network were key in modeling the emergence of activation differences (via ActFlow) in the secondary visual network and across all remaining networks. While shape completion is primarily driven by the secondary visual network, dorsal-attention regions are also involved, plausibly for relaying expectation-based signals about contour shape or position to ventral object-based areas.
bioRxiv Subject Collection: Neuroscience