Aphasia in sign language

Many scientific studies from neuroscience to linguistics show that sign language is on the same linguistic level as speech language. A study in aphasia (brain damage) can show more about the nature of language in sign language compared to speech language.

Quick facts

1) Language activities in the left brain (Broca's and Wernicke's) are found in both signed language and spoken language.

2) Language acquisition in sign language is on the similar timeline of milestones as found in speech language.

Plus, some other significant evidence. Let's jump to the aphasia studies.

What is aphasia?

Aphasia means "a communication disorder that results from damage to parts of the brain that contain language." -- American Speech-Language-Hearing Association.

Basically, production and comprehension of language are affected, intelligence is not. The linguistic regions in the left hemisphere are Broca's and Wernicke's which are responsible for language processing. Broca's is for language production and Wernicke's is for comprehension.

Aphasia studies

Neuroscience as well as linguistics studies have already shown that signed languages activate in the linguistic regions of the left brain as spoken languages do. With a minor difference, signers use a specific region of the right brain for processing spatial-visual aspect.

If Broca in the left brain is injured or damaged (expressive aphasia), ASL speakers would have difficulty with expression or production as found in spoken language lesion. Both signer and speaker with expressive aphasia alike would struggle with production, but they could understand words/signs normally.

Likewise, if Wernicke's area in the left brain is injured or damaged (receptive aphasia), a signer and a speaker alike would have a difficult time comprehending a language, but would have no problem with language production.

What does this mean? Language is amodal; that is, language is not speech-based, but rather is brain-based, regardless of the modality (signing, speech, or writing).

Aphasia in the right brain

Remember the visual-spatial processing in the right brain? What would happen if there were lesion or injury to the specifc region of the right brain in ASL speakers?

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 specific portions of the right brain is damaged, the ASL speakers would have difficulty with the spatial-visual relation (e.g. describing a room); however, they would still be able to describe a room using ASL words (e.g. "next to", "on top of", etc.) instead of using physical spatial-visual relations. Basically, language remains unaffected, except for the spatial-visual relations that can be dropped in language.

Unsurprisingly, if the right brain were damaged, a person (hearing or deaf alike) would have trouble drawing task as well as responding to spatial tasks.

It would not affect any signed language, but she/he signer may have 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".

Takeaway

Language is amodal. Both signed and spoken languages are equal in every way from language acquisition to linguistics.

More readings

Emmorey, Karen (2002). "Sign Language and Brain" Language, Cognition, and the Brain: Insights From Sign Language Reserach. Chapter 9, pp 271-314.

Harlan Lane, Robert Hoffmeister, Ben Bahan (1996). "Signed Language and the Brain". A Journey into the Deaf-World. pp 101-104.

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