Introduction: In the present study, we examined what changes in the brain occur as subjects gain a new visual skill. The subjects learned to read mirror reversed text. At first, subjects read mirror-reversed text very slowly and made many errors as they are uncertain about letters. With practice, subjects become faster and more accurate as they acquire the visual skill of reading mirror-reversed text. This study examined what changes occurred in the brain to support the acquisition and use of a new skill. Methods: Six healthy young subjects were scanned twice. First they performed a mirror-reading task without any prior practice. Secondly, they received extensive practice in reading mirror-reversed text. Finally, they were scanned again while reading mirror-reversed text. The practice made their performance far more skilled and accurate. Imaging focused on posterior cortical areas most involved in visual analysis. Results: The most striking finding was a shift in location of prominent activations from the unskilled to the skilled session. In the unskilled session, most subjects showed a prominent right parietal activation. In the skilled session, that right parietal activation decreased, but a new activation occurred in a left temporal-occipital region. Thus, the visual skill in mirror reading involved a shift from activation in one location to another. Conclusions: The present results can be interpreted in terms of neuroscience knowledge about visual pathways in the brain. It is known that the right hemisphere is dominant for spatial processes, and the left hemisphere for language processes. Thus, unskilled mirror reading may involve a great deal of visuospatial analysis of reversed letters, an analysis that depends upon right parietal areas. With skill, subjects come to know the identity of reversed letters, and can read them directly in the language-dominant left-hemisphere. Therefore, skilled mirror reading depends less upon right-hemisphere spatial capacities and more upon left-hemisphere verbal capacities. The idea that skill involves a shift from one brain pathway to another brain pathway is an intriguing one, and can only be studied by brain imaging. These finding are in press at Cerebral Cortex.
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