Bimodal bilingualism

Bimodal bilingualism is an individual or community's bilingual competency in at least one oral language and at least one sign language, which utilize two different modalities. An oral language consists of a vocal aural modality versus a signed language which consists of a visual spatial modality. A substantial number of bimodal bilinguals are children of deaf adults (CODA) or other hearing people who learn sign language for various reasons. Deaf people as a group have their own sign language(s) and culture that is referred to as Deaf, but invariably live within a larger hearing culture with its own oral language. Thus, "most deaf people are bilingual to some extent in [an oral] language in some form". In discussions of multilingualism in the United States, bimodal bilingualism and bimodal bilinguals have often not been mentioned or even considered. This is in part because American Sign Language, the predominant sign language used in the U. S., only began to be acknowledged as a natural language in the 1960s (in discussions of bimodal bilingualism in the U. S., the two languages involved are generally ASL and English). However, bimodal bilinguals share many of the same traits as traditional bilinguals (those with competency in at least two spoken languages), as well as differing in some interesting ways, due to the unique characteristics of the Deaf community. Bimodal bilinguals also experience similar neurological benefits as do unimodal bilinguals (see Cognitive effects of bilingualism), with significantly increased grey matter in various brain areas and evidence of increased plasticity as well as neuroprotective advantages that can help slow or even prevent the onset of age related cognitive diseases, such as Alzheimer's and dementia.

Most modern neurological studies of bilingualism employ functional neuroimaging techniques to uncover the neurological underpinnings of multilingualism and how multilingualism is beneficial to the brain. 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. Multilingualism, especially bimodal multilingualism, can help slow to process of cognitive decline in aging. 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. This means that the cortex must be more finely tuned, which results in a "neural reserve" that then has neuroprotective benefits. 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. In deaf signers, activation of the superior temporal sulcus is highly lateralized to the left side during facial recognition tasks, while this lateralization was not present in hearing, bimodal signers. Bilinguals also require an effective and fast neural control system to allow them to select and control their languages even while code switching rapidly. 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. 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. However, late learners who achieve full proficiency in their second language tend to show similar patterns of activation during auditory tasks regardless of which language is being used, whereas early learners tend to activate different brain areas depending upon which language is being used. 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. While hearing bimodal bilinguals showed less parietal activation than deaf signers when asked to use only sign language, those same bimodal bilinguals demonstrated greater left parietal activation than did monolinguals. Parietal activation is not typically associated with language production but rather with motor activity. Therefore, it is logical that bimodal bilinguals, when switching between speech and sign based language, stimulate their left parietal areas as a result of their increased need to combine both motor action and language production. Moreover, it has been proven that there is a parallel or simultaneous language activation during language use. This activation occurs when the bilingual uses language, regardless of the L1 or L2, being used. The dominance or lack of dominance of a language does not impact the stimulation of the brain when a language is being used. This same activation happens with any language modality, meaning the brain is activated whether the language is written, signed, or spoken. A 2021 study used event related potential (ERP) to track the brain's language switch in bimodal bilinguals and measured a brain response pattern not found in unimodal bilinguals.

To be defined as bilingual, an individual need not have perfect fluency or equal skill in both languages. Bimodal bilinguals, like oral language bilinguals, exhibit a wide range of language competency in their first and second languages. For Deaf people (the majority of bimodal bilinguals in the U. S.), level of competency in ASL and English may be influenced by factors such as degree of hearing loss, whether the individual is prelingually or post lingually deaf, style of and language used in their education, and whether the individual comes from a hearing or Deaf family. Historically, assessment of bilingual children would only measure proficiency in one of their languages. In more recent research, linguists and educators have identified this design flaw. It can be concluded that most bilingual children achieve phonological, lexical, and grammatical milestones at the same rate as monolingual children. This same phenomenon has been found in comparing unimodal bilinguals and bimodal bilinguals. In a study by Fish & Morford (2012), bimodal bilingual CODAs have demonstrated the same rate of success in these areas as their unimodal bilingual peers. Regardless of English competency in other areas, no Deaf individual is likely to comprehend English in the same way as a hearing person when others are speaking it because only a small percentage of English phonemes are clearly visible through lip reading. 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.

Like hearing oral language bilinguals, Deaf bimodal bilinguals generally "do not judge themselves to be bilingual". Whether because they do not believe the sign language to be a legitimate and separate language from the majority oral language, or because they don't consider themselves sufficiently fluent in one of their languages, denial of one's bilingualism is a common and well known phenomenon among bilinguals, be they hearing or Deaf. Code switching is a common phenomenon found among bilinguals; for bimodal bilinguals, another equivalent phenomenon is code blending, which "involves simultaneous production of parts of an utterance in speech and sign." Examples of code blending would be using ASL word order in a spoken English utterance, or conversing by showing an ASL classifier and speaking the English equivalent phrase simultaneously. Consequently, CODAs have a wide range of both positive and negative impacts based on their individual experiences.

Since linguists didn't 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.

Language shift "occurs when speakers in a community give up speaking their language and take up the use of another in its place". 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.

In more recent research related to bilingualism and ASL, early exposure and adequate access to a first language has been imperative to children's development of language, academic and social opportunities, and critical thinking and reasoning skills – all of which can be "applied to literacy development in a spoken language (such as English)." Simultaneous communication, or SimCom, which is a method of signing that represents English in its structure and elements, typically following English word order but still using one sign per word. However, research has shown this method of communication is not ideal for bilingual language learning. 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." These findings suggest that "the [teachers'] production of the less dominant language (ASL) during SimCom entails inhibition of the dominant [spoken English] language relative to the speech only condition." This study also acknowledges that SimCom is a "complex communication unit that cannot be reduced to the combination of two languages." Orthographic systems employ the morphology, syntax, lexical choices, and often phonetic representation of their target language in at least superficial ways; one must learn these new features of the target language in order to read or write. In communities where there is standardized education for the deaf, such as the United States and the Netherlands, deaf individuals do gain skill sets in reading and writing in the oral language of the community. In such a state, bilingualism is achieved between a sign language and the written form of the community's oral language. In this view, all sign–print bilinguals are bimodal bilinguals, but all bimodal bilinguals may not be sign–print bilinguals.

Children who are deaf and employ a sign language as their primary language learn to read in slightly different ways than their hearing counterparts. Much as speakers of oral languages most frequently achieve spoken fluency before they learn to read and write, the most successful profoundly deaf readers first learn to communicate in a sign language. Research suggests that there is a mapping process, in which features from the sign language are accessed as a basis for the written language, Similar to the way hearing unimodal bilinguals access their primary language when communicating in their second language. Profoundly deaf ASL signers show that fluency in ASL is the best predictor of high reading skills in predicting proficiency in written English.

There are mixed results in how important phonological information is to deaf individuals when reading and when that information is obtained. 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. Profoundly deaf children do not have access to the same auditory base that hearing children do. Yet when given sentences that are sub lexically confusable when translated into ASL, deaf readers made more errors than hearing readers. These concerning numbers are generally the result of varying levels of early language exposure. Most deaf children are born to hearing parents, which usually leaves a deficiency in their language exposure and development compared to children and parents who use the same modality to communicate. This group of children acquire a wide range of proficiency in a first language, which then impacts their ability to become proficient in a second (though sometimes possibly a first) language in the written modality. Children exposed to Manually Coded English (MCE) as their primary form of communication show lower literary levels than their ASL signing peers. However, in countries such as Sweden which have adopted a bilingual–bicultural policy in their schools for the deaf, one sees a higher literacy rate compared to school systems favoring an oral tradition.