Brain learns to sharpen its focus

Practicing a perceptual skill dramatically alters the way the visual system works, according to a study that appears in the Dec. 24, 2002 Proceedings of the National Academy of Sciences. For people tested on their ability to spot subtle visual distinctions, practice on the task beforehand results in intensified activity in the neural gateway for information from the eyes, say Sophie Schwartz of University College London and her colleagues.

In a single session, Schwartz’s group trained 16 adults to make visual discriminations using only one eye. Volunteers had to identify a central letter–either L or T, each rotated into various positions–as well as the orientation of three solid, parallel lines embedded within an array of dashed lines.

Each display, flashed briefly on a computer screen, appeared in the upper left part of the visual field and, thus, was always projected to the same small region of the primary visual cortex.

The next day, volunteers were tested on the same two-part task while a functional magnetic resonance imaging scanner measured blood flow–an indirect marker of neural activity–throughout their brains. Earlier studies had established that improvement on the task occurs only for the trained eye.

The brain scans revealed greater blood flow in the key section of the primary visual cortex as participants used their trained eyes, compared with their untrained eyes.

Structures elsewhere in the brain ramped up their activity along with that of the primary visual cortex only when volunteers used their untrained eyes, probably because of the greater demands of having to perform a task without training. These data support the theory that learning translates into more efficient localized brain activity.

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