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Poster E6, Friday, November 10, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

A sensitive period for the modification of the language network in blindness

Rashi Pant1, Shipra Kanjlia1, Connor Lane1, Marina Bedny1;1Johns Hopkins University

Evidence from blindness suggests that regions outside of the classic language network can be recruited for language processing as a result of early experience. In congenital blindness, in addition to classical language areas, visual cortices also become involved in language processing. (Roder et al., 2002, European JoN.;  Amedi et al., 2004, Nat Neuro;  Bedny et al., 2011, PNAS). Here we asked whether this modification of the language network follows a sensitive period. Do visual cortices also take on linguistic functions in adult-onset blindness? Previous studies find that in congenitally blind people, visual cortices are more active during auditory sentence processing than during a control task with non-words (Roder et al., 2002, European JoN; Bedny et al., 2011, PNAS; Lane et al., 2015, JoN). Furthermore, in congenitally blind but not blindfolded sighted individuals, activity in the visual cortex increases with the grammatical complexity of sentences, showing greater activation for sentences with syntactic movement than for matched sentences without it  (Lane et al., 2015, JoN). We scanned 11 adult-onset blind (blindness onset after age 17) participants during the same auditory sentence comprehension and working memory control tasks used by Lane et al. (2015) and compared their visual cortex activity to that of 18 congenitally blind adults and 17  blindfolded sighted participants.  All blind participants had at most minimal light perception and were blind due to pathology of the eyes or optic nerves. Participants heard a sentence followed by a yes/no question about who did what to whom. Half the sentences contained syntactic movement, i.e. had an object-extracted relative clause. In the working-memory-control task participants listened to a list of non-words (target list) followed by a shorter probe list. Participants decided whether the order of non-words in the probe matched the order of the same non-words in the target. We found that the visual cortex of adult-onset blind participants responded to sentences more than non-words when compared to the sighted participants, but this effect was much smaller than in the congenitally blind (P < 0.05). Furthermore, unlike in the congenitally blind, the degree of response to sentences in visual cortex correlated with the duration of blindness over the course of decades (r = 0.73, P < 0.05), suggesting a different mechanism of plasticity in adulthood. Crucially, unlike the visual cortex of the congenitally blind, the visual cortex of adult-onset blind participants did not respond to grammatical complexity (group-by-condition interaction P < 0.05), suggesting that the visual cortices play a less specific role in linguistic processing in this population. In sum, we find that even in adulthood, cortical areas that did not evolve for language processing can become responsive to spoken language. However, these responses are less specific and qualitatively different from cortical specialization for language during development and may not be functionally relevant to sentence processing.

Topic Area: Language Development

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