[1] A substantial number of bimodal bilinguals are children of deaf adults (CODA) or other hearing people who learn sign language for various reasons.
Neuroimaging and other neurological studies have demonstrated in recent years that multilingualism has a significant impact on the human brain.
The mechanisms required by bilinguals to code-switch (that is, alternate rapidly between multiple languages within a conversation), not only demonstrate increased connectivity and density of the neural network in multilinguals, but also appear to provide protection against damage due to age and age-related pathologies, such as Alzheimer's.
It is thought that this is a result of the increased work load that the executive system, housed mostly in the frontal cortex, must assume in order to successfully control the use of multiple languages at once.
Gray matter volume (GMV) has been shown to be significantly preserved in bimodal bilinguals as compared to monolinguals in multiple brain areas, including the hippocampus, amygdala, anterior temporal lobes, and left insula.
Similarly, neuroimaging studies that have compared monolinguals, unimodal bilinguals, and bimodal bilinguals provide evidence that deaf signers exhibit brain activation in patterns different from those of hearing signers, especially in regards to the left superior temporal sulcus.
Evidence indicates that the left caudate nucleus—a centrally located brain feature that is near the thalamus and the basal ganglia—is an important part of this mechanism, as bilinguals tend to have significantly increased GMV and activation in this region as compared to monolinguals, especially during active code-switching tasks.
[6] As implied by the significant preservation of gray matter in the hippocampi (an area of the brain largely associated with memory consolidation and higher cognitive function, such as decision-making) of bimodal bilinguals, areas of the brain that help control phonological working memory tend to also have higher activation in those individuals who are proficient in two or more languages.
There is also evidence that suggests that the age at which an individual acquires a second language may play a significant role in the varying brain functions associated with bilingualism.
For example, individuals who acquired their second language early (before the age of 10) tend to have drastically different activation patterns than do late learners.
[7] Along with the neuroprotective benefits that help to prevent onset of age-related cognitive issues such as dementia, bimodal bilinguals also experience a slightly different pattern of organization of language in the brain.
Additionally, many Deaf bilinguals who have fluency in written English choose not to speak it because of the general social unacceptability of their voices, or because they are unable to monitor factors like pitch and volume.
ASL has traditionally not even had the status of being considered a legitimate language, and Deaf children have been prevented from learning it through such "methods" as having their hands tied together.
Despite the fact that Deaf children's early exposure to ASL has now been shown to enhance their aptitude for acquiring English competency, the unequal social status of ASL and English, and of sign languages and oral languages, remains.
Since linguists did not recognize ASL as a true language until the second half of the twentieth century, there has been very little acknowledgment of, or attention or study devoted to, the bilingual status of the American Deaf community.
The author of the paper covered many contact sign approaches in complex layers of ASL and spoken English expressions.
Simultaneously, Deaf people still often have a need or desire to learn some form of English in order to communicate with family members and the majority culture.
[15] Bimodal bilinguals are able to produce and perceive a spoken and a signed language simultaneously compared to those who are unimodal.
[20] However, those who are able to produce and perceive a spoken and signed language simultaneously demonstrated a slower speech rate, decreased lexical richness, and lower syntactic complexity when compared to the results of the speech-only condition.
[20] In addition, ASL users rely more on pragmatic inferences and background context versus syntactic information.
"[13] This conclusive research emphasizes the need for more additive models of bilingual education, as opposed to subtractive or transitional models of education, which are designed to shift the learner away from the native language for the goal of complete use and reliance of the majority language.
In a study about bimodal bilingual teachers and students' vocabulary levels, the results revealed a "slower speech rate, lower lexical richness, and lower syntactic complexity in the SimCom [teaching] condition compared with the speech-only condition."
[24] In addition, highly proficient signing deaf children use more evaluative devices when writing than less proficient signing deaf children, and the relatively frequent omission of articles when writing in English by proficient signers may suggest a stage in which the transfer effect (that normally facilitates deaf children in reading) facilitates a mix of the morphosyntactic systems of written English and ASL.
Alphabets, abugidas, abjads, and syllabaries all seem to require the reader/writer to know something about the phonology of their target language prior to learning the system.
[24] In 2012, "About one in five deaf students who graduate from high school have reading skills at or below the second grade level; about one in three deaf students who graduate from high school have reading skills between the second and fourth grade level.
[24] Children exposed to Manually Coded English (MCE) as their primary form of communication show lower literary levels than their ASL signing peers.