INTERHEMISPHERIC-TRANSFER OF VISUAL PERCEPTUAL-LEARNING IN CALLOSAL AGENESIS

Accession number da ISI Web of Science WOS:A1992HR69400008 Abstract: 1. A young boy, with agenesis of the corpus callosum, but with intact anterior commissure, has been subjected to three experiments to test his visual functions. Apart from dilatation of the lateral ventricles, related to the absence of the callosum. Nuclear Magnetic Resonance (NMR) images did not reveal any other sign of abnormality. 2. Visual evoked potentials were recorded in response to a pattern stimulus in the left visual field. in the presence of a contralateral stimulus. Under conditions in which the latter depresses the response to the former in normal subjects (contralateral stimulus separated 1 deg from the vertical visual field midline). no significant depressing effect was obtained in the acallosal subject. A depressing "cross-midline" effect was present at 0.25 deg from the midline. 3. Depth discrimination was evaluated for central vision by a two-rod test and found to be deficient in the acallosal subject for disparities exceeding 30 min arc (coarse stereopsis). 4. Interhemispheric transfer of perceptual learning in a pattern discrimination task was present in the acallosal subject. As in normals. this transfer was limited to regions of the visual field mirror symmetric with respect to the vertical midline. In this respect, his interhemispheric transfer was not deficient.