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Sensory Modality and Spoken Language Shape Reading Network in Blind Readers of Braille

Poster D66 in Poster Session D with Social Hour, Friday, October 7, 5:30 - 7:15 pm EDT, Millennium Hall

Mengyu Tian¹, Elizabeth Saccone¹, Judy Kim², Shipra Kanjlia³, Marina Bedny¹; ¹Department of Psychological and Brain Sciences, Johns Hopkins University, ²Department of Psychology, Yale University, ³Department of Psychology, Carnegie Mellon University

The neural basis of reading is highly consistent across languages and scripts (Rueckl, 2015, PNAS). All scripts studied thus far recruit regions of ventral occipitotemporal cortex (vOTC), which contains a posterior/anterior word-form gradient: a progressively changing preference from simple visual features (posterior) to larger orthographic structures (anterior) (Vinckier, 2007, Neuron). What anatomical principles constrain the neural basis of reading? Does the sensory modality of written symbols (tactile vs. visual) influence their neural representations? To address these questions, we compared the neural basis of Braille reading in proficient congenitally blind readers (n=19) to that of visual print in sighted readers (n=19). Based on connectivity theories of brain function, we hypothesized that regions in parietal cortex, with strong connectivity to early somatosensory cortices, play a special role in Braille reading. Additionally, we tested effects of reading hand and spoken-language lateralization on the laterality of Braille. We hypothesized that the effect of reading hand would decrease, and effect of spoken language would increase, along the processing hierarchy. Participants were presented with written (real words, consonant strings, non-letter control shapes) and spoken stimuli (real words, backward speech) that varied in word-likeness. To ensure attentive processing, participants read/heard blocks of 6 stimuli, then judged whether a probe stimulus was present during the block. Consistent with connectivity-based predictions, individual-subject ROI analysis revealed that PPC of blind readers contains patches that prefer Braille over spoken language and tactile control stimuli. No such pattern was observed in sighted readers, supporting the hypothesis that PPC develops specialization for Braille. Data-driven topographic maps further showed the most anterior portions of PPC, immediately adjacent to S1, prefer tactile control shapes, whereas posterior PPC and parieto-occipital cortex prefer Braille words. A vector-of-ROIs analysis along the anterior/posterior extent of PPC revealed a position-by-reading condition interaction in blind readers. In contrast, in sighted readers, most areas of the PPC preferred visual shapes, with no differences in responses to visual and auditory stimuli. The response profile in blind readers suggests an anterior-to-posterior Braille processing stream: with anterior regions supporting recognition of tactile patterns and posterior regions performing Braille-specific, orthographic processing. This gradient is analogous to the posterior-to-anterior gradient observed in vOTC of sighted print readers. With respect to Braille laterality, we observed effects of both reading hand and spoken-language lateralization but with different anatomical distributions. The effect of reading hand was strongest at early stages of processing (the hand regions of S1), weaker at intermediate stages (in PPC and vOTC), and absent in inferior frontal cortex (IFC). By contrast, the effect of spoken language on laterality of Braille increases along the processing hierarchy from PPC to vOTC and peaking in high level language region (IFC). These results suggest that written and spoken language co-lateralize regardless of reading modality. In sum, the neural basis of visual and print reading is constrained by connectivity, the entry point of symbols to the cortex (S1 vs. V1) and the neural basis of spoken language. These common principles give rise to different anatomical distributions across Braille and visual print.

Topic Areas: Reading, Development