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Baboons offer glimpses of left-brain brawn.

Look at the letter "S" in the SCIENCE NEWS 1ogo on the cover and manipulate the image in your mind's eye. Rotate it to various angles and you still recognize the letter, without confusing "S" with its mirror image. Researchers have generally considered this a uniquely human ability that depends on the specialized functions of the brains left and right sides.

But a new study finds that baboons can mentally rotate images and still recognize them, the first such demonstration in a nonhuman species. And thanks to an experimental procedure that delivers visual information to one side of the brain or the other, the researchers also conclude that the baboon's left hemisphere orchestrares this accomplishment.

"Our data clearly challenge the theory that only humans have brain hemispheres that evolved to serve different functions," contends psychologist William D. Hopkins of Emory University in Atlanta. He and his collaborators French psychologists Jacques Vauclair and Joel Fagot, both of the National Scientific Research Center in Marseilles-will present their results in the March PSYCHOLOGICAL SCIENCE.

Their paper comes on the heels of growing evidence that monkeys and other nonhuman primates favor one hand over the other for particular tasks, an indirect sign that their brain hemispheres perform specialized functions (SN: 1/7/89, p.10). Right-brain superiority in identifying faces has emerged among "split-brain" monkeys, but it remains unclear whether surgically cutting off communication between hemispheres alters other aspects of brain function.

Hopkins and his co-workers employed a technique developed in the late 1980s and first used in human studies. Its extension to nonhuman primates represents "a breakthrough for animal cognition researchers:' asserts psychologist Jeannette P Ward of Memphis (Tenn.) State University.

Six baboons and three humans learned to control a cursor on a computer screen with a joystick and to align it with a fixation point in the center of the screen. They then saw either the "sample" letter "F" or "P" flash to the left or right of the square for about one-tenth of a second.

For both humans and monkeys, if a letter or other stimulus appears to the left of a fixation point for a period faster than the one-fifth of a second needed for the eyes to focus on the stimulus, it enters only the left visual field and gets processed only by the right hemisphere. Speedy presentation to the right of the fixation point delivers a stimulus to the left hemisphere via the right visual field.

Next, two "comparison" letters flashed for one-tenth of a second just above and below the center square; one was the original letter, the other its reversed image. Baboons moved the cursor to the position of the comparison letter that they thought matched the sample. letter and received food pellets for correct answers. On a series of trials, comparison letters were tilted at progressively sharper angles, thus requiring mental rotation for a correct response.

Baboons proved highly accurate at the task only after left-brain exposures to letters. Human volunteers did well with both hemispheres, but prior studies with larger samples have found a left-brain advantage for mental rotation o! meaningful symbols such as letters, Hopkins notes. Both humans and baboons took longer to respond as comparison letters departed more sharply from the sample position.

Overall, baboons performed mental rotations more than twice as fast as humans. Baboons treated the letters as meaningless shapes, whereas humans may have engaged in more laborious processing of both meaning and shape, Hopkins suggests.

His group plans to study hemispheric function among chimpanzees and other monkey species by facing them with the same mental rotation tasks.
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Title Annotation:brain hemisphere specialization
Author:Bower, Bruce
Publication:Science News
Date:Jan 23, 1993
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