Paczynska, M. | Search bioRxiv

bioRxiv2025

Semantic representations in the visual cortex of blind and sighted humans

In blind humans, the "visual" cortex responds to linguistic stimuli, such as words and sentences. This is sometimes taken as evidence that this brain region supports starkly different computations in blind and sighted individuals. Here, we challenge this view and show that, during word processing, the visual areas in these two populations represent the same semantic dimension - the knowledge about physical properties of word referents. Using analysis of fMRI activation patterns, we found that the visual cortex in both congenitally blind and sighted participants represented differences between individual words. In both groups, the activation patterns for words in the visual cortex reflected physical, but not conceptual similarity between word referents. Furthermore, the between-group correlations in these activation patterns were comparable to within-group correlations. Finally, during word processing, the visual areas in both groups showed greatest "representational connectivity" to the occipitotemporal areas. Overall, our findings suggest that responses to linguistic stimuli in the visual cortex of blind individuals are driven by representational mechanisms that are functional also in the sighted adult brain. In sighted individuals, information about physical properties of word referents might be backprojected to visual areas, from the occipitotemporal cortex, to support visual predictions, imagery, and visuospatial thinking. In blind individuals, this mechanism might be preserved and, combined with increased excitability of the blind visual cortex, drive strong responses of this region to linguistic stimuli.

neuroscience↗

bioRxiv2024

Neural representation of nouns and verbs in congenitally blind and sighted individuals

Language processing involves similar brain regions across languages and cultures. Intriguingly, one population escapes this universal pattern: in blind individuals, linguistic stimuli activate not only canonical language networks, but also the "visual" cortex. Theoretical implications of this finding are debated, particularly because it is unclear what properties of linguistic stimuli are represented in the blind visual cortex. To address this issue, we enrolled congenitally blind and sighted participants in an fMRI experiment, in which they listened to concrete, abstract, and pseudo nouns and verbs. We used multi-voxel pattern classification to investigate whether differences between nouns and verbs are represented in the blind visual cortex, and whether this effect is modulated by the words semantic category. The classification of activation patterns for nouns and verbs was above chance level in the motion-sensitive area V5/MT in the blind participants, but not in other visual areas in this group. The effect in area V5/MT was driven by successful classification of activations for concrete nouns and verbs, in the absence of significant results for abstract and pseudo nouns and verbs. These findings suggest that the blind visual cortex represents the physical properties of noun and verb referents, more salient in the concrete word category, rather than more abstract linguistic distinctions, present in all word categories. Thus, responses to language in the blind visual cortex may be explained by preserved ability of this region to compute physical and spatial representations of the world. Significance StatementIn sighted individuals, language processing involves similar brain regions across languages. Intriguingly, in blind individuals, hearing words and sentences activates not only the canonical language network, but also the "visual" cortex. What is computed in the visual cortex when blind individuals process language? Here, we show that a specific visual area in the blind - the motion-sensitive area V5/MT - responds differently to spoken nouns and verbs. We further showed that this effect is present for concrete nouns and verbs, but not for abstract or pseudo nouns and verbs. This suggests that, during language processing, the blind visual cortex represents physical features of word referents, more salient in the concrete word category, rather than more abstract linguistic distinctions, present across word categories.

neuroscience↗