Elsevier

Cortex

Volume 27, Issue 2, June 1991, Pages 345-350
Cortex

Limitations of Interhemispheric Extracallosal Transfer of Visual Information in Callosal Agenesis

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Abstract

A 57-year-old patient with callosal but not anterior commissure agenesis was investigated with a visual interfield comparison and a naming task. Stimuli were presented tachistoscopically either bilateral-simultaneously or unilaterally in the LVF and/or RVF. The stimuli presented bilaterally differed with respect to their degree of similarity. Whereas the patient was able to detect gross differences between stimuli presented in the left and right half-field, he was impaired at discriminating similar and identical stimuli across the half-fields. Identification by naming was correct on unilateral presentation of a stimulus, while with bilateral presentation of two stimuli, errors increased considerably with the stimulus named second. The data are thought to indicate a limited capacity of the extracallosal commissures, probably the anterior, for the transfer of visual information.

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a

H.O. Karnath, Abt. Neurologie (Poliklinik), RWTH Aachen, Pauwelsstrasse, D-5100 Aachen, F.R.G.