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 "Non accommodating bilingualism and the brain" 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. 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. 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.
The results provide insight into the resilience and constraints of neural plasticity for language and bilingualism. 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. For example, left hemisphere inferior frontal and temporal regions demonstrate resilience in their support of language functions despite variations in language modality signed or spoken or the number of languages used monolingual or bilingual; Petitto et al.
In contrast, 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. However, our understanding of how the brain accommodates sign language and bilingualism is incomplete without a better appreciation of bimodal bilinguals, bilinguals who can both hear a spoken language and learn a sign language, from early life Petitto et al. Here we explore the resilience and plasticity of the brain's organization for human language as an outcome of early bilingual language experience to a sign and a spoken language.
Sign languages are visuo-spatial languages. Researchers have been investigating how early exposure to a sign vs. Bilateral parietal regions, known to be important for analyzing body motion and visuo-spatial orientation in hearing monolinguals, appear to become selectively engaged for sign language morpho-syntax Corina et al. Importantly, there is also evidence of neuro-developmental plasticity, only adults who received early exposure to a sign language show right parietal recruitment during signing Neville et al.
Hence, 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. Yet, it also remains that there are differences in functional language organization between deaf and bimodal signers in these resilient regions for language.
A key notable difference between bilinguals and monolinguals is the increase in greater gray matter density in left parietal regions in unimodal spoken language bilinguals relative to monolinguals Mechelli et al. That study found that high proficiency bilinguals who learned their two languages before the age of 5 had the Non accommodating bilingualism and the brain increase in gray matter density relative to low proficiency and later exposed bilinguals, as well as monolinguals Mechelli et al.
Several studies have shown that unimodal spoken language bilinguals also typically show greater signal intensity in left inferior frontal regions during lexico-semantic Kovelman et al.
Yet, it remains generally unknown if these differences predominantly stem from frequent competition between bilinguals' two languages Abutalebi et al. Research into bimodal bilinguals who potentially experience reduced competition between their two languages in non-overlapping auditory and visual modalities may
Non accommodating bilingualism and the brain new light on the nature of the brain's accommodation for two languages.
There are many critical similarities between bimodal and unimodal spoken language bilinguals. Specifically, young learners of a sign and a spoken language reach their first word and Non accommodating bilingualism and the brain linguistic milestones at the same time as unimodal bilinguals Petitto et al.
Young bimodal and unimodal bilinguals also show similar trajectories of vocabulary growth across their two languages in the first 3 years of life Holowka et al. Regarding language switching, bimodal bilinguals can use both languages at the same time while unimodal bilinguals can only use their two languages in alternation because both languages cannot be expressed simultaneously from the mouth.
On the other hand, it has been found that young bimodal bilinguals show unimodal-like patterns of language switching in response to their family's switching habits, interlocutor's language, and the morpho-syntactic structures of their languages Petitto et al. Hence, one can hypothesize that all types of Non accommodating bilingualism and the brain, bimodal and unimodal, have a similar impact on language organization in the brain.
Nevertheless, it is possible that bimodal bilingualism makes a lesser impact on the bilingual brain relative to unimodal bilingualism. For instance, theories of bilingual cognition have put forth a hypothesis and supporting evidence that the necessity to switch between two languages from early in life can enhance a bilingual child's and adult's attentional capabilities Bialystok,; Bialystok et al. However, this effect has not been found in young bimodal bilinguals Emmorey et al.
Another typical point of competition between two languages is lexico-semantic encoding of homophones, or words that sound the same across languages but can often mean different things. Specifically, plain and plane are English homophones that sound the same but have different meanings, the same phenomenon is possible across bilinguals' two different languages Finkbeiner et al.
Such type of Non accommodating bilingualism and the brain competition is not possible for bimodal bilinguals.
Given the evidence that there is reduced levels of competition between sign and spoken languages relative to two spoken languages, could it then be possible that bimodal bilingualism does not change the brain beyond the specific accommodations for the person's sign and spoken languages? What impact might dual language experience and language switching have for a bilingual brain? Neuroimaging studies of bilingual language switching have found greater activation in bilateral prefrontal and left temporo-parietal regions during language switching tasks in unimodal bilinguals as compared to using only one language at a time Hernandez et Non accommodating bilingualism and the brain. The only study that has investigated language switching bimodal bilinguals found that this group only showed greater activation in left temporo-parietal regions during the switching condition as compared to non-switching and as compared to English monolinguals Kovelman et al.
In that study, we hypothesized that increased activation in temporo-parietal regions in bimodal bilinguals stemmed from the competition between bimodal bilinguals' lexico-semantic representations in the two languages Kovelman et al. Nevertheless, it remains possible that increased activation in left the temporo-parietal region was due to the engagement of sign-specific language processes in the parietal regions Newman et al.
The limitation of the previous study was that it only compared bimodal bilinguals to spoken language monolinguals. Hence, to fully answer the question on how the brain accommodates to bimodal bilingualism it is critical to also compare bimodal bilinguals to Deaf signers.
Most of the previous research examined the impact of early sign language exposure as compared to late sign language exposure or spoken language exposure e. Here we explore the impact of early bimodal bilingual exposure to a sign and to a spoken language in hearing adults as compared to early ASL sign language exposure in deaf adults.
The goal of the present study is to broaden our understanding of the resilience and of the brain's organization for language in light of both bilingual and bimodal exposure to two languages in different modalities.
There is limited sensory-motor and lexical competition between sign and spoken languages because they do not compete for the same sensory-motor apparatus and do not use similar phonetic features to encode words. Thus, the bimodal bilingual brain requires little additional neural adjustments for language processing beyond the plasticity necessary for accommodating the given spoken and sign languages. Early bilingual exposure will lead to evidence of the Non accommodating bilingualism and the brain neural accommodation for processing two language systems, both in the brain's resilient regions that are universal for language processing across sign and speech, including left frontal and temporal regions and the plastic regions specific to sign language processing including the parietal regions.
Thus, we can predict differences across bilingual ASL-English signers and functionally monolingual deaf ASL signers during the unimodal use of sign language. The present study addressed these two hypotheses by testing three groups of participants: This task was chosen because it is known to engage frontal, sensory-motor, temporal, and parietal brain regions known to demonstrate both resilience and plasticity in their functional organization for bilingualism and sign language exposure Mechelli et al.