Let's look at the nature of language and the brain, the common assumptions, and the facts based on the hard science, specifically neuroscience, and lingusitics.
In a few situations, when a hearing person asked me (and some other Deaf alike), "Do you hear anything? Wear hearing aids? Do you [vocally] speak?"
"No. No. No."
"How do you read and write so well?" Once a British retired former-school-principal asked me. Once a fellow graduate student asked me.
Because, speech is not central to language. We learn English through eye -- e.g. writing/reading.
"But, writing depends on speech (or the sound)."
Never mind. Language is amodal. Language is based on the brain, regardless of the modalities.
"Language is not mouth stuff – it's brain stuff.” – Dr. William Stokoe, the father of ASL linguistics.
Linguistics and neuroscience studies debunk common assumptions and misconceptions about the nature of language by studying signed languages:
Myth: "Speech is essential for human language acquisition."
Fact: language is amodal. It means...
"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)
Most of you are familiar with the fact that the left regions (Broca and Wernicke) of the brain process language. In neuroscience studies, when ASL is used, it activates the same left regions of the brain.
Myth: "Speech is essential for the human brain to have typical brain organization and processing of human language."
Fact: On the contrary, tissues in the brain for language are not processing sounds, but patterns.
Myth: "Early exposure to sign language will hurt a child's acquisition of spoken language."
The fact is that children who are exposed to ASL early in life are stronger in the acquisition of spoken/written English (a benefit of bilingualism).
Myth: "Exposing a child with a cochlear implant to sign language will hurt (auditory) tissue development."
Research shows that sign language exposure early in life with a cochlear implant doesn't hurt the development of the (auditory) tissue. Using a signed language does not hinder nor delay speech development.
Myth: "Babies can sign earlier than speak."
Linguistics studies show that language acquisition in signed language is on the same timeline as spoken language from babbling to one-word stage to pronoun reveral errors at about 20 months.
If Wernicke's area in the left brain were damaged or injured in an accident (receptive aphasia), a signer and a speaker alike would have a difficult time comprehending a language, but would have no problem with language production.
On the other hand, if Broca's area in the left brain were damaged (expressive aphasia), both signer and speaker alike would struggle with production, but they could understand words/signs normally.
Fluent signers use the same left regions of the brain for language processing as the (vocal-auditory) speakers do. In addition, they do use a small portion of the right brain because of the nature of visual-spatial use in sign language. Let's look at an interesting discovery.
If the right brain were damaged, a person would have trouble drawing task as well as responding to spatial tasks. Now if there were a damage to a signer's right brain, it would not affect any (signed) language, but the signer would experience difficulty describing a room using spatial relations (spatial-visual processing); instead she/he would sign "CHAIR UNDER TABLE ACROSS-FROM (or NEXT-TO) BED)" instead of "TABLE CL:B | CHAIR CL:2-under-table".
Aren't bilingual or multilingual plus bimodal or multimodal people super-lingual?
The findings from Dr. Petitto's scientific studies show the results that "Deaf children, who are exposed to signed languages from birth, acquire these languages on an identical maturational time course as hearing children acquire spoken languages" from the syllabic babbling stage to the first word stage and the two-word stage and beyond.
Furthermore, she noted, "hearing children, who are exposed exclusively to signed languages from birth through early childhood, achieve each and every linguistic milestone in signed language on the identical time course as has been observed for hearing children acquiring spoken language and deaf children acquiring signed language."
"The brain is organized for language, not for speech." -- Karen Emmorey.
Dr. Petitto concluded that the differences of language acquisition and linguistic milestones between spoken and signed language were "no greater than the differences between language acquisition of one spoken language (e.g. French) versus another (e.g. Italian)".
These studies basically suggest that the human brain has no favor for speech over signing. It's people who are audist.
"Sign language is the equal of speech, lending itself equally to the rigorous and the poetic, to philosophical analysis or to making love." -- Oliver Sacks.
Petitto, Dr. Laura Ann. Untitled. Montreal: McGill University media. October 28, 1997.
Newman, A.J., Bavelier, D., Corina, D., Jezzard, P. and Neville, H.J. A critical period for right hemisphere recruitment in American Sign Language processing. Nature Neuroscience, 5:76-80, 2002.
Laura Ann Petitto. "On the biological, environmental and neurogenetic factors determining early language acquisition: evidence from signed and spoken languages."
Emmorey, K., & McCullough, S. (2008). "The bimodal bilingual brain: Effects of sign language experience", Brain and Language , doi:10.1016/j.bandl.2008.03.005
Karen Emmorey. "Sign Language and the Brain". Language, Cognition, and the Brain: Insights From Sign Language Research. Chapter 9: pp 271-314.
Lane, Harlan, et al. (1996) A Journey into the Deaf-World. DawnSignPress. Pp 101-104.
This Gallaudet's video explains all key information in short on the brain, language, modality (signing and speech), language acquisition, and myths and facts on cochlear implants.
Related posts: Sight and the brain of Deaf people.
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