A sensitive period in the neural phenotype of language in blind individuals

Abstract

In congenital blindness, "visual" cortices respond to linguistic information, and fronto-temporal language networks are less left-lateralized. Does this plasticity follow a sensitive period? We tested this by comparing the neural basis of sentence processing in two experiments with adult-onset blind (AB, n=16), congenitally blind (CB, n=22) and blindfolded sighted controls (n=18). In Experiment 1, participants made semantic judgments for spoken sentences and solved math equations in a control condition. In Experiment 2, participants answered "who did what to whom" questions for grammatically complex (with syntactic movement) and grammatically simpler sentences. In a control condition, participants performed a memory task with lists of non-words. In both experiments, visual cortices of CB and AB but not sighted participants responded more to sentences than control conditions, but the effect was much larger in the CB group. Crucially, only the "visual" cortex of CB participants responded to grammatical complexity. Unlike the CB group, the AB group showed no reduction in left-lateralization of fronto-temporal language network relative to the sighted. These results suggest that blindness during development modifies the neural basis of language, and this effect follows a sensitive period.

Naturalistic stimuli reveal a critical period in visual cortex development: Evidence from adult-onset blindness

“…The reduced inter-subject correlations in visual cortex among the AB group, relative to the CB group, observed in the current study is consistent with previous experimental studies reporting reduced or absent cross-modal activity in adult-onset blind individuals (Bedny et al, 2010, 2012; Cohen et al, 1999; Jiang et al, 2016; Kanjlia et al, 2019; Pant et al, 2020; Sadato et al, 2002). We find that both in whole-cortex analyses and in focused analyses examining V1 responses, the AB group was different from the CB and no different from the sighted.…”

“…At least one TMS study comparing adult-onset and congenitally blind adults supports this view (Cohen et al, 1999; see also Amedi et al, 2004). The present results, together with prior literature further show that cross modal responses in people born blind are more anatomically extensive and robust, occur under different stimulus conditions, and are more sensitive to subtle cognitive manipulations (e.g., Pant et al, 2020; Kanjlia et al, 2016; Lane et al, 2015). Thus, while cross-modal effects are present in visual cortices of all people, early blindness substantially modifies the character of these responses.…”

“…Indeed, several studies have found some activity in visual cortices of adult-blind onset individuals during effortful tasks that involve making on-line decisions. For example, cross-modal activity has been reported when adult-onset blind participants make button presses or verbal responses to indicate semantic judgments in response to individual words and sentences (Aguirre et al, 2016; Burton et al, 2003; Burton, Snyder, Diamond, et al, 2002; Burton & McLaren, 2006; Pant et al, 2020). Notably, even when observed, such responses are weaker than those seen in visual cortices of people born blind during the same tasks.…”

“…There is also evidence that visual cortices of people who are born blind show subtle sensitivity to higher-cognitive information that is absent in people who become blind as adults. For example, only congenitally blind people show enhanced visual cortex activity for grammatically complex sentences over more simple sentence constructions and respond more for complex than simple math equations (Kanjlia et al, 2019; Pant et al, 2020).…”

Speech Perception Triggers Articulatory Action: Evidence From Mechanical Stimulation

“…Somatosensory brain areas, moreover, have been implicated in multiple functions. "Visual" brain areas are engaged by tactile (Kauffman et al, 2002) and auditory (Amedi et al, 2007;Striem-Amit et al, 2012) inputs, and they can even mediate syntactic processing in both blind (Bedny et al, 2011) and sighted individuals (Elli et al, 2019;Pant et al, 2019). Deaf signers, by contrast, are known to engage speech motor areas during the production of signs (Martino et al, 2017).…”