Jude Stromberg

The Neuropsychology of American Sign Language

     It is well established that language exists
predominantly in the left hemisphere.  Kimura (1993)
states that the earliest knowledge of brain asymmetry
comes from Dax and Broca.  They report speech disorders
in left hemisphere lesioned patients as early as the
1860's.  Currently, the scope of research supporting
brain asymmetry is immense.  
     The left hemisphere is also reported to control
proximal movement of both arms.  Manual apraxia,
difficulty in carrying out complex, fine motor skill
movements with the hands and arms without the presence of
weakness or immobility, is demonstrated in persons left
hemisphere cerebral damage(Kimura, 1993).  While not
associated with spoken language per se, expressive
gestures using the hands are certainly forms of
communication.  This assumption is the link between these
two left hemisphere functions.  
     Aphasia, disruptions in speech due to central
nervous system damage, and apraxia are both often
associated in patients with left hemisphere damage. 
Nowhere can this relationship between the left hemisphere
and language (both spoken and symbolic) be better
demonstrated than in users of American sign language
(ASL).
     Manual sign language has existed as a language for
ages.  Ancient indigenous cultures used a combination of
spoken and signed words to communicate.  Signed language
has, and continues to, provide silent conversation (for
hunting, etc.), communication between unfamiliar groups,
and enabling deaf people to communicate (Kimura, 1993).
     Of all signed languages, ASL is the most widely
studied.  ASL exhibits organization similar to spoken
languages, providing a level of communication that
specifies the precise ways units are put together to form
complex signs (words) and how these signs are further
manipulated to form sentences.  This is parallel to
morphological and syntactic levels of speech production. 
ASL also shares organizational similarities such as
syllables, sentence fragments, lexical levels, and rules
based upon underlying forms (subject-verb agreement)
(Corina et al., 1992).
     Research suggests that ASL is fractionated into
sublexical units similar to spoken languages.  Signs are
distinguished from one another by: 1)hand posture,
2)hand/arm orientation with respect to the body, 3)
location on the body, and 4)movement.  Many signs employ
the same posture, but exist in different relations to
each other and to the body (Kimura, 1993).  Broken down
even farther, ASL has segmental structure that is
concurrent with spoken language phonemes and syllables.
     Many other styles of sign language exist besides
ASL.  Each has their own history and style.  Each form
differs in such slight, but precise ways, that a signer
learning a new language will have an "accent" because
they will include small style differences from their
original language.  
     ASL also has grammatical devices that yield
inflection.  These exist as small, precise changes in
handshape, movement, and location.  Consider the word
GIVE.  By utilizing small changes give can mean: give me,
give continuously, give to each one, give to each
continuously, give to each in turn, and give to each in
turn continuously.  Such manipulations in hand shape,
movement, and location provide the signers the
opportunity to speak in tenses, to use suffixes and
prefixes, and to determine verb conjugation (Corina et
al., 1992).
     In spoken languages, previous items are related to
latter items via grammatical devices and structure.  ASL
can accomplish this by changing the relationship of the
same sign in space, as space bears linguistic meaning. 
Such "compositionality" (van Gelder, 1990) exists in all
true language.  At every level of communication, units
are broken down into a hierarchical pattern to convey
meaning.
     All of this alludes to ASL's legitimacy as a true
language.  A distinction now needs to be made, as not all
signed language exists in such an organized pattern. 
Legitimate sign language (ASL or other) differs from non-
sign language (pantomime) by several distinct
differences.  Pantomime is often a continuous movement
with no well-defined transitions.  Also, movements of the
head and body are included to suggest meaning.  Given
this, true sign language consists of discrete hand
shapes, locations, movements, and orientations, while
pantomime is more generic; an acted out metaphor.  This
distinction is important as it provides researchers  with
a means of determining how brain damage is manifested in
signers.
     As previously suggested, language exists primarily
in the left hemisphere.  Also, complex motor movements
are left hemisphere driven.  There are several schools of
thought relating these two phenomena's (Corina et al.,
1992).  First, due to both of the above observations the
left hemisphere is uniquely predisposed to language
function.  Second, the left hemisphere's specialization
for language (spoken and signed) is a result of the its
general role in controlling oral and manual articulation. 
Third, expression and comprehension of symbols underlie
the left hemisphere's language predisposition.  The study
of ASL in lesioned deaf persons provide great insight
into this debate.
     Hendren (1989)suggested that sign language was a
right hemisphere occurrence because pantomime, gesturing
and symbolizing are all right brain functions.  His
argument was regarded as "clearly wrong" by Hines (1991)
who suggests that sign language is clearly a left
hemisphere function because language, definitely left
hemisphere, is the "par excellence of symbolizing". 
Also, he states research by Poizner, Klima, and Bellugi
(1987).  They declare that damage to the traditional
language areas produces serious impairments on signers
ability to sign, while right hemisphere produces little
or no effect.  Also, damage to specific areas of the left
hemisphere produce problems similar to aphasia found in
spoken language.
     Corina et al. (1992) performed extensive research on
left lesioned signers.  They found left hemisphere
specialization of both signed and spoken language in deaf
and hearing persons, respectively.  Also, no evidence of
asymmetry was found for the production of pantomime in
their subjects.  They reviewed a case study of a left
hemisphere lesioned signer who demonstrates the ability
to use pantomime post-lesion, but who is severely aphasic
for sign language.
     Perhaps the best support for left hemisphere control
of ASL comes from Corina et al. (1992).  They report a
case study on W.L., a 76 year old congenitally deaf right
handed male who grew up signing.  Previous to his stroke
W.L. did a 2 hour interview in ASL.  This provides the
opportunity for exact comparison of his pre- and post-
lesion abilities.
     Previous to his stroke W.L. used a full range of
grammatical ASL devises and absolutely no pantomime. 
After a lifetimes experience at ASL he was obviously an
expert.  
     A post lesion CAT scan indicated a lesion in the
frontotemporalparietal area of the left hemisphere.  Sign
language diagnostic profiles determined that W.L. became
very sign language aphasic for both comprehension and
production.  His grammatical form was compromised
markedly by the use of uninflected verbs, fewer nouns,
and no pronouns.  His signing produces many paraphasias
and neologisms, and inconsistencies were discovered in
both hands.  He was very poor at finding the correct
signs and in explaining observations.  However, he
demonstrated no spatial-visual deficits, which in
concurrent with the bulk of similar literature.
     W.L. was compared to S.M, a right hemisphere damaged
signer, for visual-spatial task ability..  S.M. elicited
no aphasia, but he did show marked spatial-visual task
problems, unlike W.L., who performed excellently at such
tasks.  However, when asked to name as many animals as
possible in 60 seconds, W.L. came up with only 3, while
the average is 25.  Several of his signs were pantomime
in nature and were, therefore, excluded.
     When asked to describe a picture, W.L. grasped the
story, but failed to explain it using ASL.  Instead he
opted for pantomime and illustrated sever sign aphasia. 
When the researchers analyzed 17 mistakes made by W.L.
they found 17 hand shape errors and 3 movement errors,
but no errors in location or orientation.  This suggests
that W.L.'s errors were phonological in nature.  
     Finally, W.L. demonstrated a remarkable use of
pantomime.  Typically, pantomime was used to elaborate
upon his signs or replace them altogether.  This is
important because it demonstrates a separation of
nonlinguistic and linguistic language, even though both
are expressed via hand movements.  
     All of this demonstrates that language, both spoken
and signed, are predominately left hemisphere
occurrences.  Because fine-motor skills are also left
hemisphere controlled, there are those that believe sign
aphasia is a result of this.  As W.L. and other subjects
demonstrate, sign usage is impaired, but pantomime isn't
indicating that the "language" and not the "manipulation"
aspect of the left hemisphere is faulty. 


                      BIBLIOGRAPHY
                            
Corina, D.P., Poizner, H., Bellugi, U., Feinberg, T.,  
   Dowd, D., and O'Grady-Batch, L.  Dissociation     Between
   Linguistic and Nonlinguistic Gestural   Systems: A Case
   for Compositionality.  Brain and   Language.  43: 414-447.
   1992.

Corina, D.P., Vaid, J., and Bellugi, U.  The Linguistic
    Basis of Left Hemisphere Specialization.  Science.
    255: 1258-1260.  1992.

Hendren, G.  Using Sign Language to Access Right Brain
     Communication: A Tool for Teachers.  Journal of
     Creative Behavior.  23: 116-120.  1989.

Hines, T.  The Myth of Right Hemisphere Creativity.
    Journal of Creative Behavior.  25:223-227.  1991. 

Kimura, D.  Neuromotor Mechanisms in Human Communication. 
    New York: Oxford University Press.  1993. 

Poizner, H., Klima, E., and Bellugi, U.  What the Hands
    Reveal About the Brain. Cambridge, MA: MIT Press.
    1987.

van Gelder, T.  Compositionality: A Connectionist
    Variation on a Classical Theme.  Cognitive Science.
    14: 355-384.  1990.   

Copyright © 1997, Dr. John M. Morgan, All rights reserved - This page last edited March 17, 1997
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