Beyond the Visual Word Form Area: Characterizing a hierarchical, distributed and bilateral network for visual word processing

Although the left hemisphere (LH) Visual Word Form Area (VWFA) is considered the pre-eminent cortical region engaged in visual text processing, other regions in both hemispheres have also been implicated. To examine the entire circuit, using functional MRI data, we defined ten regions of interest (ROI) in each hemisphere that, based on functional connectivity measures, naturally grouped into early vision, high-level vision, and language clusters. We analysed univariate and multivariate responses to words, inverted words, and consonant strings for ROIs and clusters, and demonstrated modulation by text condition bihemispherically, albeit more strongly and in a larger number of regions in the LH. Graph theory analysis revealed that the high-level vision cluster and, specifically, the VWFA was equivalently connected with both early visual and language clusters in both hemispheres, reflecting its role as a mediator in the circuit. Our findings reveal bihemispheric, stimulus-mediated ROI response flexibility but circuit-level connectivity stability, reflecting the complex contribution of a distributed system for word processing.