Posted 2012, updated 2016.
These quick facts, according to the hard sciences such as neuroscience and linguistics, are an overwhelming evidence that signed language is on par with spoken language.
1) Neuroscience studies (Petitto) show that ASL activates the same linguistic regions of the left brain as English or any languages.
2) Studies show that children (whether hearing or deaf) exposed to sign language undergo the same language development milestones as children exposed to speech language -- from babbling to the one-word stage and then the two-word stage.
3) Signed languages have all linguistic features in linguistics as found in spoken languages -- phonology (the smallest units of language), morphology (how words are formed), syntax, and so on.
These three things -- the linguistic regions of the brain, the similar language developmental milestones, and the existence of sign-language linguistics -- indicate that language is amodal. What does it mean? Language is not central to speech.
"The human brain does not discriminate between the hands and the tongue. People discriminate, but not our biological human brain." -- Dr. Laura-Ann Petitto (Gallaudet Today, Spring 2012, p. 17)
Here are some highlights of the myths and facts on speech and language based on Dr. Petitto's works and many other studies.
Assumption: hearing people commonly believe that speech is superior. They believe that speech is the avenue to language acquisition. They believe that speech and language are directly linked.
Fact: Neroscience and linguistics studies defy those beliefs, showing hard science evidence that language is amodal, which means that visual-spatial modality is on a par with vocal-aural modality, and language is brain-based.
Assumption: Speech is paramount to language acquisition.
Fact: Language acquisition studies show that both visual-spatial language (e.g. ASL or any signed langauges) and vocal-aural language (e.g. English or any spoken languages) are on the same timeline of language acquisition milestones from birth from babbling to two-word stage.
Assumption: The auditory tissue in the brain was thought to be for auditory processing. "Exposing a child with a cochlear implant to sign language will hurt 'auditory' tissue development."
Fact: Hearing/eyeing speakers process signed language and spoken language in the "exact same tissue". It has nothing to do with sound; rather, it has to do with the patterns of language.
Assumption: Deaf children (with cochlear implants) must have an intensive speech therapy and sign language must be avoided at all costs, because early exposure to sign language will impair the acquisition of English and/or speech.
Fact: This speech-only approach more likely may impair language development. Speech is not a language. It's a modality. The crucial thing is to develop a language regardless of modality. Bilingualism (ASL and English) provides deaf children language acquisition and the benefits of being bilingual and bimodal (e.g. visual processing advantages that hearing children lose). Bilingual-bimodal children have stronger language skills, even in reading.
"Researchers have found that if a child has none of that training, if a young child does not have that phonological training, if they only have ASL phonological exposure, they end up better readers and writers. This provides evidence of the fact that ASL does not harm one's ability to develop literacy or skills in English." (Petitto) I can attest to the fact that many bilingual-bimodal children (whether hearing or deaf) of bilingual Deaf ASL-speaking parents have advanced reading skills.
Most agree that the earlier you expose a child to a language, the easier it is for that child to pick it up. The same rules apply to sign language for deaf children.
According the studies, early exposure to sign language in addition to spoken language for all deaf children is the best way to maximise linguistic and cognitive skills to overcome any delays or difficulties due to deafness.
La Trobe University's Dr Adam Schembri—Director of the National Institute for Deaf Studies and Sign Language—and colleagues examined the effects of age of acquisition in deaf adults who use British Sign Language (BSL).
This study is focused specifically on deaf adults and reports significant accuracy differences for those who acquire sign language as a delayed first language between 2 to 8 years of age, but also significantly slower response times for those who acquire sign language as a second language in later life,' says Dr Schembri.
The study showed children that develop sign language skills from birth had better grammatical judgement in BSL. For adults who reported learning BSL from the ages of 2 to 8 years, the study found it harder for people to acquire the same language skills.
'One thing that seems very clear is that successful early acquisition of a first language is crucial, whether that language is natural signed language, such as BSL (or Auslan in Australia), or a spoken/written language such as English,' says Dr Schembri.
The current study supports many others showing that early exposure to accessible language is much more likely to result in successful language acquisition than later exposure.
'The advantages of early sign language exposure remain clear even with rapid advances in hearing aids and cochlear implants.'
According to Dr Schembri, an approach using both sign language and a spoken or written language will be the most beneficial for children to make the most of their linguistic skills.
'Bilingual education is the best way of ensuring that deaf children have early exposure to both a signed language and a spoken/written language, which will provide the deaf child with the best chance for successful language acquisition, in either or both languages.
We know that bilingualism comes with a range of cognitive benefits, so we would advocate early bilingualism in both signed and spoken language for all deaf children,' says Dr Schembri.
The Study—First Language acquisition differs from second language acquisition in prelinqually deaf signers: Evidence from sensitivity to grammaticality judgement in British Sign Language—was published in Cognition and is available on request.
La Trobe University, Australia. May 29, 2012.
Compare the milestones of language acquisition in signed language with that of spoken language. And, observe the phonological acquisition in sign language.
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