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Stroke victims illuminate brain's grammar.

Stroke victims illuminate brain's grammar

Two women who suffered brain-damaging strokes in 1985 have given scientists a glimpse at apparently different mechanisms by which the brain handles written and spoken words belonging to the same grammatical class, such as nouns or verbs.

In fact, the women provide the first clear evidence that different brain systems -- devoted either to speaking or writing words -- distinguish grammar categories separately, assert neuropsychologists Alfonso Caramazza of Johns Hopkins University and Argye E. Hillis of HealthSouth Rehabilitation Corp., both in Baltimore. Previous studies of brain-impaired people suggested that the brain separately processes nouns by a variety of categories, such as fruits and vegetables, animals, inanimate objects and proper nouns (SN: 8/10/85, p.85).

One of the study participants, a 62-year-old right-handed former salesperson referred to as H.W., experienced a stroke near the back of her brain's left hemisphere. The other woman, a 48-year-old right-handed librarian dubbed S.J.D., sustained stroke-induced damage toward the front of her left hemisphere.

The researchers asked each woman to read aloud and to write from dictation a list of 296 nouns and verbs, and then to orally name and write 60 pictured objects and actions. Both women made a significant number of errors, but only with verbs, not nouns. Where H.W. had trouble pronouncing verbs, S.J.D. displayed problems only in writing verbs, Caramazza and Hillis report in the Feb. 28 NATURE.

Further testing with homonyms -- words that assume different meaning as a noun or verb while maintaining the same written or spoken form -- indicates that the womens' language deficits involve the processing of words when used as verbs, not an impairment in producing specific words regardless of their grammatical affiliation, the investigators say.

In written homonym tests, experimenters read the women a sentence and then asked them to write an emphasized word in the blank space of a typed sentence. For example, for the noun form of the word "crack," the women heard "There's a crack in the mirror; write 'crack,'" and then filled in the partial sentence "There's a [[[[[ in the mirror." For the verb form, the women heard "Don't crack the nuts in here; write 'crack'" and again filled in the blank in an incomplete sentence.

The reading test required the participants to read a sentence silently, and then to pronounce an underlined word in that sentence -- such as the word "crack" in the two sentences above.

H.W. displayed marked difficulty only with reading aloud homonym verb forms, while S.J.D. performed poorly only when asked to write homonym verb forms, the researchers observe.

These findings suggest that a word's grammatical identification gains representation "separately and redundantly" in brain systems that process either written or oral vocabulary, Caramazza and Hillis contend. Such a precise divvying up of brain functions concerned with word meanings poses a challenge to recent theories (based on work with "neural network" computers) that reject the need for rule-based language systems in the brain, the researchers add. These theories assume instead that different patterns of activation among large numbers of brain cells associate words with their meanings.
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Title Annotation:how the brain handles words
Author:Bower, Bruce
Publication:Science News
Date:Mar 2, 1991
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