PET STUDIES OF PARIETAL INVOLVEMENT IN SPATIAL ATTENTION - COMPARISONOF DIFFERENT TASK TYPES

Abstract Five experiments are described that concern the mechanisms th at direct attention to spatial and non-spatial features of a stimulus and the effects that attention has on the visual system's analysis of that stimulus. Shifts of attention from one spatial location to anothe r activated the superior parietal lobe and this activation was fairly independent of the task performed on the attended object, the response made to the attended object, and whether the shift of attention was c ontrolled endogenously or exogenously. Maintaining attention tonically on a location or a particular visual feature such as shape, colour or motion did not produce a superior parietal response. Tonic attention to a feature (colour, shape, motion) or location, however, did produce enhancements in the response of various regions that are probably spe cialized for processing the attended visual feature. The activation of superior parietal cortex during shifts of spatial attention as well a s the activation of parietal-occipital cortex when attention is tonica lly maintained on a location suggest that the parietal cortex plays an important role in spatial computations.