Abstract
Early bilingual exposure, especially exposure to two languages in different modalities such as speech and sign, can profoundly affect an individual's language, culture, and cognition. Here we explore the hypothesis that bimodal dual language exposure can also affect the brain's organization for language. These changes occur across brain regions universally important for language and parietal regions especially critical for sign language (Newman et al., 2002). We investigated three groups of participants (N = 29) that completed a word repetition task in American Sign Language (ASL) during fNIRS brain imaging. Those groups were (1) hearing ASL-English bimodal bilinguals (n = 5), (2) deaf ASL signers (n = 7), and (3) English monolinguals naïve to sign language (n = 17). The key finding of the present study is that bimodal bilinguals showed reduced activation in left parietal regions relative to deaf ASL signers when asked to use only ASL. In contrast, this group of bimodal signers showed greater activation in left temporo-parietal regions relative to English monolinguals when asked to switch between their two languages (Kovelman et al., 2009). Converging evidence now suggest that bimodal bilingual experience changes the brain bases of language, including the left temporo-parietal regions known to be critical for sign language processing (Emmorey et al., 2007). The results provide insight into the resilience and constraints of neural plasticity for language and bilingualism.
Highlights
Studying bilinguals for whom sign language is one of their two languages provides a better way of understanding both the resilience and plasticity of human language and the underlying brain regions that support it
The present findings suggest that hearing native American Sign Language (ASL)-English bimodal bilinguals had reduced neural recruitment of the left parietal region relative to the deaf native ASL users
We suggest that the neural demands/impact of early bilingual language exposure may influence the functional organization of the left parietal brain region in ways that, in turn, offer a possible explanation of the observed differences between our bimodal bilinguals and our native sign language users
Summary
Studying bilinguals for whom sign language is one of their two languages provides a better way of understanding both the resilience and plasticity of human language and the underlying brain regions that support it. The parietal brain regions, classically associated with visuo-spatial processing, show evidence of plasticity and become specialized for processing sign language structure (Neville et al, 1997; Newman et al, 2002; Emmorey et al, 2005). Researchers have suggested that learning a sign language across both deaf and hearing individuals may change the functionality of the parietal regions supporting sign language processing (Neville et al, 1997; Corina et al, 1999; Newman et al, 2002). It remains possible that there are differences in functional language organization between deaf and bimodal signers in these
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