Left Brain Reigns over Sign Language
Bower, Bruce, Science News
Left brain reigns over sign language
Traditional notions of brain function hold that the left hemisphere controls spoken language while the right hemisphere calls the shots regarding visual and spatial skills, including those necessary for using sign language. But converging lines of evidence, underscored by a report in the July 24 NATURE, indicate that this assumption is wrongheaded.
Rather, the ability to use and understand sign language, in which hand movements and their manipulation in space are critical to meaning, appears to be rooted in the left brain hemisphere, according to the new study, headed by Antonio Damasio of the University of Iowa College of Medicine.
"The lef hemisphere's specialization for language appears to rest more on its ability to transform labels into meanings regardless of the modality of a language [spoken or signed]," says Damasio.
His interpretation is based on the rare opportunity to study a hearing individual who is also proficient in sign language, before and after damage to a critical portion of her right hemisphere. The 27-year-old woman, who works as an interpreter and counselor at a community agency for deaf people, sought surgical treatment after drug therapy failed to quell her persistent seizures. Images of the right-handed subject's brain, taken while she listened and responded to a spoken language task, revealed increased activity in left hemisphere language centers.
The researchers then injected a barbiturate drug, sodium amobarbital, into an artery leading into her left hemisphere in order to shut down temporarily these language areas. The subject was initially unable to identify a series of objects in either English or sign language. Correct English responses appeared about 2 1/2 minutes before the first correct sign language responses accurred. During that short period, the woman was able to identify many objects verbally while simultaneously using incorrect hand shapes and movements for the same objects. …