Spatial attention in agenesis of the corpus callosum: shifting attention between visual fields.

The role of the corpus callosum in spatially selective visual attention is uncertain. Research using commissurotomy and callosotomy patients has attempted to determine if the corpus callosum plays a role in reorienting attention between visual fields, as if spatial attention is unitary or divisible between the cerebral hemispheres. Reorienting of selective visuospatial attention within versus between visual fields was tested in 10 individuals with agenesis of the corpus callosum (ACC) and nine matched controls. Spatially focused attention to the most likely location of target appearance was created using both peripheral sensory cues and central symbolic cues in separate tests. Results demonstrated that individuals with ACC have significantly greater difficulty reorienting attention to an invalidly cued target stimulus occurring in the opposite visual field. However, this effect did not interact with the type of cueing (sensory or symbolic). Individuals with ACC did not differ from controls either with respect to the laterality of within-field reorientation of attention, or with respect to the most efficient direction of between-field shifting of attention. Since congenital absence of the corpus callosum significantly reduces efficiency in the reorienting of attention between visual fields, spatial attention cannot be completely unified based on a subcortical mechanism and the mobilization of attentional resources within each hemisphere must depend on callosal processes. Copyright 2002 Elsevier Science Ltd.