Visuospatial tasks compared via activation of regional cerebral blood flow.

Regional cerebral blood flow was measured in 19 subjects during the performance of three tasks thought to primarily involve right hemisphere processing: judgement of line orientation, mental rotation of three-dimensional cube arrays, and a fragment puzzle task. Asymmetries in hemispheric flow (right side greater) were only observed in the line orientation and rotation conditions and were present in both sexes. The magnitude of the asymmetry was greater in the rotation task which also showed an asymmetry in parietal flow. Thus mental rotation placed the most asymmetric demand on cerebral resources. This provides a task that more reliably activates the right hemisphere than those previously reported and suggests a truly "mental manipulative" aspect to right hemisphere advantage in visuospatial performance.