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Left-brain snow job.

Left-brain snow job

An epilepsy patient whose right and left brain hemispheres have been surgically disconnected to control his seizures sits in a laboratory. Researchers flash a picture of a chicken claw in his right visual field (processed by his left hemisphere) and a picture of a snow scene in his left visual field (handled by his right hemisphere). Next they spread an array of pictures before him and ask him to pick the ones associated with the pictures he has just viewed.

With his right hand he chooses a picture of a chicken, and with his left hand he chooses a picture of a shovel, both correct responses. But when asked why he chose those items, the man replies: "Oh, that's easy. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed."

What's behind his fowl logic? As in most people, says psychologist Michael S. Gazzaniga of Dartmouth Medical School in Hanover, N.H., the man's left hemisphere handles complex thinking skills, such as language, and makes inferences about how the world works. Thus, his left brain interprets the picture of the shovel consistently with what it already knows -- chicken feet, not snow.

Researchers have documented hundreds of similar observations with "split-brain" patients, Gazzaniga notes in the Sept. 1 SCIENCE. In contrast, it appears the right hemisphere is poor at making inferences and seeing causal relationships on its own. Gazzaniga concludes there is a left-brain "interpreter" that generates hypotheses about thoughts and emotions triggered by specialized brain regions throughout both hemispheres.

The left-brain interpreter is a unique aspect of human evolution, in Gazzaniga's opinion. It "not only presents the human species with a mechanism to both form and modify beliefs, but perhaps also frees [us] from the shackles of environmental stimuli," he contends.

In split-brain patients, whose brain hemispheres can have separate and isolated experiences, the left-brain interpreter creates a sense of conscious unity, even if that means recruiting a wayward chicken shed.
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Title Annotation:left and right brains
Publication:Science News
Date:Sep 23, 1989
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