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Visual skills show two-pronged development.

A new study suggests that there's more to some visual feats than meets the eye, not to mention the brain.

Improvement in performing rapidly presented visual tasks peaks within minutes of practicing these skills and stays stable for at least eight hours after training ends. At that point, performance of the tasks gets an unexpected boost from apparently permanent brain changes sparked by the initial learning, assert two neuroscientists in the Sept. 16 NATURE.

"It's surprising that there's such a high level of plasticity in the adult brain for what we think of as hard-wired visual processes," says Avi Karni of the National Institute of Mental Health in Bethesda, Md. "The learning of many sensory and motor skills may proceed in two stages separated by a latent period of at least several hours."

Karni conducted the research with Dov Sagi of the Weizmann Institute of Science in Rehovot, Israel.

In test sessions, each of nine adults watched a computer screen on which flashed a square-shaped "test" image of several hundred dashes encasing three horizontally or vertically oriented lines. A "mask" pattern then flashed on the screen, composed of randomly oriented V-shaped characters intended to interfere with visual processing of the first image. Presentation of each test and mask image took less than a second.

Participants identified the orientation of the angled lines following each presentation. Over a series of 800 to 1,200 trials per person, the researchers gradually narrowed the fleeting gap between the appearance of test images and mask patterns. Accuracy at the task rose sharply over the first several hundred trials and then leveled off.

Yet about a half day later, in the absence of intensive practice, volunteers displayed further large improvements in performing the visual task. Moreover, they retained these gains over a two- to three-year follow-up period.

The initial learning of some perceptual skills apparently sparks several hours of cerebral "consolidation," assert Karni and Sagi. During this period, small groups of brain cells undergo as yet poorly understood changes that boost an individual's sensitivity to the sensory task at hand and promote long-lasting memory for the skill, they contend.

Their conclusion contradicts a longstanding scientific assumption that practice produces improvement on various perceptual skills in a direct way, with no delayed effects. However, the new data coincide with an emerging view that the brain contains a plethora of cell groupings devoted to different tasks, rather than a general mechanism that orchestrates all sorts of learning.

"Some types of perceptual experience trigger permanent neural changes in early processing stages of the adult visual system," Karni and Sagi propose. "These may take many hours to become functional."

The scientists cannot explain how particular groups of brain cells produce two phases of learning separated by several hours of silent consolidation. A chemical messenger in the brain, acetylcholine, may play an important role in facilitating consolidation after initial learning, Karni contends.

In another study recently completed by the same researchers, volunteers practiced similar rapidly presented visual tasks in the evening and performed the tasks again about eight to 12 hours later, after waking up in the morning. Disruption of rapid eye movement (REM) sleep in some participants blocked their delayed improvement on the task and erased previous gains from training. Acetylcholine levels rise significantly during REM sleep, Karni says. Disturbing sleep at other times did not interfere with consolidation.

"Consolidation is an active neural process that can be stopped," Karni holds.
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Title Annotation:adult learning
Author:Bower, Bruce
Publication:Science News
Date:Sep 18, 1993
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