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“Tactile word form” responses in parieto-occipital cortices of proficient blind braille readers
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Abby Clements1, Elizabeth Saccone1, Mengyu Tian2, Marina Bedny1; 1Johns Hopkins University, 2Beijing Normal University
Reading recruits specialized neural populations in the lateral ventral visual stream (vOTC), including the so-called ‘visual word form area’ (VWFA). The VWFA neighbors other visual object recognition regions, including the fusiform face area and parahippocampal place area, but is functionally and anatomically distinct. One hypothesis for the consistent location of the VWFA across individuals is that it is optimized for connectivity between visual and language networks. Here we test the hypothesis that, analogously, blind braille readers to develop braille specialization in anatomical regions that interface between touch and language. Posterior parietal cortices (PPC) participate in high-level tactile perception (Saadon-Grosman, Arzy, & Loewenstein, 2020; Rolls et al., 2023). Moreover, neurobiology of language is changed in blindness and blind individuals recruit ‘visual’ cortices during spoken language processing. Here we report that posterior parietal/dorsal-occipital regions (PPC-DOC), at the border of tactile and occipital language networks, are functionally specialized for braille in people born blind. Congenitally blind braille readers (N = 20) participated in two experiments. In Experiment 1, participants read braille words and consonant strings, touched shapes made from braille dots, and listened to spoken words and backwards speech. In Experiment 2, blind participants touched small 3D models of faces and small maze-like ‘places.’ Sighted participants (N = 20) performed analogous visual experiments. We tested whether blind readers develop responses to braille in PPC-DOC that prefer braille over speech and over tactile face and scene perception. An individual-subject leave-one-run-out analysis identified voxels in PPC-DOC that respond more to braille words than shapes made of braille dots (t(19) = 4.6, p < 0.001). These voxels also prefer braille words to spoken words (t(19) = 4.7, p < 0.001). Consistent with a specialized-for-braille hypothesis, braille-preferring voxels also failed to distinguish between faces and scenes (t(19) = 0.3, p = 0.79). By contrast, separate neural populations in parietal cortices responded preferentially to tactile faces and tactile places, respectively (p’s < 0.001), and these voxels did not prefer braille or spoken words over the associated controls. In fact, face-preferring neural populations responded more to tactile shapes than to braille words (t(19) = 2.4, p = 0.028), mirroring the functional profile observed in vOTC of sighted readers. Overlap maps of the voxel populations across subjects revealed bilateral responses to braille, with a different anatomical distribution from face and scene responses. Braille responses were relatively consistently localized across blind readers (up to 50% of subjects overlap), peaking on the parieto-occipital border, in area V3a. In sighted participants, this parieto-occipital region is retinotopic and motion-sensitive (Tootell et al., 1997; McKeefry et al., 2008.) We also observed variation of braille response peaks along the anterior/posterior axis across individuals. Our results suggest that tactile reading recruits a differently localized orthographic processing circuit. We hypothesize that development of modality-specific orthographic representations is shaped by connectivity to the language network and sensory input systems.
Topic Areas: Reading,