Brain network mechanisms of visual shape completion

Abstract 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. Significance StatementVisual shape completion is a fundamental process that combines scattered edge elements into unified representations of objects. The process has been extensively investigated in humans and animals, but neural studies have focused on lateral occipital and early visual regions with scant regard to given other parts of cortex or their functional interconnections. Here, we employed recent methods in network neuroscience and functional MRI to show that visual shape completion modulates a densely interconnected set of cortical regions; these primarily occupy the secondary visual network but may also be found in four other networks. Dorsal attention regions played a surprisingly prominent role in modeling activity within secondary visual network and across all remaining networks during shape completion.