Intra- and interhemispheric processing of visual information in callosal agenesis.

Two siblings with total callosal agenesis were compared with two control groups on a number of tachistoscopic tasks involving unilateral and bilateral presentation of verbal and nonverbal stimuli. Acallosals were able to effect intra- and interhemispheric comparisons and to correctly identify all kinds of stimuli in either visual field. However, they responded more slowly, especially in the bilateral condition where they also made more errors than the controls. The results are interpreted in terms of increased use of extra-callosal commissures.