Lost it at the produce counter – memory loss
Robert J. Trotter
Lost it at the produce counter Almost everyone knows the foolishness of trying to compare apples with oranges. But consider the case of a patient named M.D., who has trouble telling the difference between the two.
In 1981, M.D. suffered a stroke that damaged a portion of his brain involving the left frontal lobe and the basal ganglia. The result was global aphasia, loss of the power to use or comprehend words. Within 18 months, M.D. had almost totally recovered from his aphasia and performed well on a standard language test, though he complained that he still had considerable difficulty with certain words. Further testing revealed that his word problems centered on two specific categories–fruits and vegetables.
M.D.’s unusual problem offered psychologist John Hart Jr. and his colleagues a rare opportunity to study the organization of language in the brain. Researchers have previously reported on people whose brain damage left them better at naming inanimate objects than they were at naming living things and food. M.D.’s “striking disability” in naming fruits and vegetables is much more selective and suggests that the mental lexicon, or dictionary, is organized by specific categories in specific areas of the brain.
During more than a year of testing, researchers evaluated M.D.’s language abilities with a battery of tests. His scores were almost perfect, except when it came to fruits and vegetables. When shown drawings, photographs and real objects from a variety of semantic categories, for example, he could name almost all of them. However, when confronted with drawings, photographs and real pieces of fruits and vegetables, M.D. could name only 63 percent of them.
On another test, M.D. was shown pictures of 75 items and asked to sort them according to their semantic classification and to name the categories. The items included fruits, vegetables, animals, vehicles and food products. Again, M.D.’s mistakes consisted entirely of confusions between fruits and vegetables. And when he was asked to list as many names as possible from 17 categories, he was able to name only about six fruits and vegetables within one minute, but an average of 12 items in each of the other 15 categories.
In another test M.D. was given 10 definitions of fruits and vegetables and 10 definitions of other items, including animals, furniture and clothing. He named only two fo the fruits and vegetables but identified all of the other items. When allowed to touch but not see various fruits and vegetables, he was able to identify only 6 of 13 fruits and 11 of 21 vegetables. He correctly identified 11 of 12 items in other categories.
Based on these tests, the researchers conclude that M.D.’s problem appears to be a “selective disturbance” within the brain’s semantic system.
To test this possibility, the researchers developed a 45-item word/picture matching test tht required M.D. to point to one of two pictures after the name of one was said aloud to him. M.D. pointed immediately and with certainty to the fruits and vegetables after hearing their names. Further, he was able to categorize correctly the written names of fruits and vegetables–the same ones whose pictures he could not categorize.
So it appears that M.D. knows as much as he ever knew about fruits and vegetables, he just can’t name them and thereby gain access to what he already knows. And since this disability is limited to only two related semantic categories, the researchers conclude that the brain’s dictionary, which may contain as many as 75,000 words, is organized according to specific categories that can be affected by localized brain damage.
Hart is at Johns Hopkins University. Rita Sloan Brendt, at the University of Maryland Hospital, and Alfonso Caramazza, at Johns Hopkins University, cowrote the report, which appeared in Nature (Vol. 316, No. 6027).
COPYRIGHT 1985 Sussex Publishers, Inc.
COPYRIGHT 2004 Gale Group
