Lexical and Semantic Coding in the Occipital Cortex of Sighted and Blind

Abstract

How early visual cortex (EVC) supports language and semantic processing in sighted and congenitally blind individuals remains debated. Some predict that blindness induces radical functional reorganization of EVC, whereas others suggest more modest scaling-up changes of a neurofunctional architecture present in sighted individuals. We recorded whole-head MEG in 19 early blind (EB) and 21 sighted adults (SC) listening to spoken adjectives belonging to different semantic categories (i.e., abstract, concrete visual, concrete non-visual) and performing lexical and semantic decision tasks. In the lexical task, lexical information (i.e., word vs pseudoword) could be reliably decoded in perisylvian language areas and the EVC of both groups, with group differences (EB > SC) localized to occipital areas between 0.4 and 0.8 s after word onset. During the semantic task, semantic category information could be decoded in a network overlapping with the canonical semantic system and encompassing the EVC of both groups, with group differences (EB > SC) localized to occipital areas between 0.9 and 1 s after stimulus onset. We further characterized EVC properties and showed that i) EVC semantic information decoding is task sensitive, with no above-chance decoding in EB or SC in the lexical task ii) in the blind EVC it was possible to decode abstract from concrete concepts but not visual from non-visual concepts, a profile similar to that of posterior cingulate areas, but different to anterior cingulate cortex which showed above chance classification for all semantic categories. These results suggest that deprived EVC is integrated into a distributed lexical-semantic network carrying behaviourally relevant semantic information, although to a different extent.