Interhemispheric differences in visual attention.

The chapter explores the difference between the cerebral hemispheres in the three categories of attention described in the fundamental classification of Posner and Petersen: Alerting, Orienting, and Executive Functions. The first section is concerned with the brain localization of visuospatial attention as studied in brain-damaged patients, mainly hemineglect and callosum-sectioned patients. Other important results have been provided more recently by means of brain imaging studies of cortical and subcortical attention networks. Most of these studies have shown a clear dominance of the right hemisphere (RH) in visuospatial attention, but there are some exceptions. Accordingly, the second section concerns the role of the left hemisphere (LH) in visuospatial attention. A third section describes the contribution of attention to interhemispheric communication. A fourth section is focused on a discussion of the existence of hemispheric asymmetries not only in conscious but also in unconscious attention. Further, a fifth section concerns the effects of emotion on hemispheric differences in visuospatial attention. Finally, the last section briefly discusses the controversial evidence concerning laterality in executive functions.