Semantic coding in the occipital cortex of early blind individuals

Abstract

The visual cortex of early blind individuals is reorganized to support cognitive functions distinct from vision. Research suggests that one such prominent function is language. However, it is unknown whether the visual cortex of blind individuals codes for word meaning. We addressed this question by comparing neuronal activity evoked by a semantic decision task, using magnetoencephalography (MEG), between 12 early blind and 14 sighted participants otherwise comparable with regard to gender, age and education. We found that average brain responses to thousands of auditory word stimuli followed similar time courses in blind and sighted participants. However, in blind participants only, we found a sustained enhancement of activity in the visual cortex. Moreover, across the whole brain, we found an effect of semantic category from about 400 ms after word onset. Strikingly, in blind participants, semantic categories were discriminable starting 580 ms after word onset from signal captured by sensors sensitive to the visual cortex. We replicated the analyses in time windows locked to stimulus onset and behavioral response, using both classical hypothesis testing and machine learning for singletrial classification. Semantic decisions were well classified in all participants (AUC ~ 0.60), but generalization capacity across participants was found reduced in the blind group due to a larger variability of discriminative patterns. In conclusion, our findings suggest that brain plasticity reorganizes the semantic system of blind individuals, and extends semantic computation into the visual cortex.

Naturalistic audio-movies reveal common spatial organization across “visual” cortices of different blind individuals

“…Some prior evidence supports the idea that cortical functional specialization is somewhat more variable across blind than sighted people. Previous studies find that laterality patterns vary to a greater extent across blind than sighted people (Lane et al, 2017;Abboud et al, 2019). This could contribute to lower alignment in visual cortex in the current study.…”

“…This could contribute to lower alignment in visual cortex in the current study. Consistent with the idea of greater individual variability of cortical map across blind individuals, a recent MEG study revealed that semantic categories of auditory word stimuli were decodable from occipital cortex of blind individuals when analyses were performed at the individual-subjects level; however, cross-subject generalization was unreliable, indicating considerable variability in neural responses across blind individuals (Abboud et al, 2019). Together with prior findings, the present results provide both evidence for presence of reliable visual cortical maps across people who are blind and evidence that cortical alignment across people is somewhat reduced in blind relative to sighted people.…”

“…Most neuroimaging studies of visual cortex plasticity in blindness have targeted a single cognitive process (e.g., sound localization, language) using simplified experimental designs (e.g., Poirer et al, 2006;Thaler et al, 2011). A handful of studies have identified anatomically separable responses to two or three information types within "visual" cortices of blind people (e.g., language vs. math) (Kanjlia et al, 2016;Abboud et al, 2019). Recent studies find that the ventral occipitotemporal and early visual cortices of people born blind show spatially distinct responses to stimuli from different semantic categories (e.g., faces and places) when these are presented either via touch or auditorily (van den Hurk et al, 2017;Mattioni et al, 2020;Ratan et al, 2020;Vetter et al, 2020;Pietrini et al, 2004).…”

Diferencias en la Corteza Visual Primaria Entre la Ceguera Congénita, Temprana y Tardía. Una Revisión Sistemática

“…[12][13][14] No obstante, V1 tiene relación no solamente con la información auditiva y táctil, sino también con la memoria y el lenguaje. Existen diversos estudios 8,13,[15][16][17][18][19] en los cuales V1 se activa en tareas de lenguaje (ya sea mediante Braille o de forma auditiva) y memoria operativa (semántica y aritmética) con mayor intensidad en sujetos con ceguera temprana o congénita.…”

Spoken language comprehension activates the primary visual cortex

“…However, unlike association regions, the primary visual cortex of people born blind has also been shown to respond to tasks quite remote from visual processing, such as language comprehension and production (Abboud et al, 2019; Bedny et al, 2011a; Burton et al, 2003; Burton et al, 2002b; Dietrich et al, 2013; Lane et al, 2015; Röder et al, 2002). Although evidence for language activation is compelling, persuasive evidence for a mechanism by which such extreme functional reorganization might occur has not been provided to date: for example, beyond deterioration of the visual pathways (Noppeney et al, 2005; Shimony et al, 2006; Shu et al, 2009; Yu et al, 2007), no drastic differences in anatomical connectivity of the visual cortex were found between congenitally blind people and sighted controls.…”