Selective Dorsal and Ventral Processing: Evidence for a Common Attentional Mechanism in Reaching and Perception

Abstract

The primate visual system can be divided into a ventral stream for perception and recognition and a dorsal stream for computing spatial information for motor action. How are selection mechanisms in both processing streams coordinated? We recently demonstrated that selection-for-perception in the ventral stream (usually termed “visual attention”) and saccade target selection in the dorsal stream are tightly coupled (Deubel & Schneider, 1996). Here we investigate whether such coupling also holds for the preparation of manual reaching movements. A dual-task paradigm required the preparation of a reaching movement to a cued item in a letter string. Simultaneously, the ability to discriminate between the symbols “E” and “∃” presented tachistoscopically within the surrounding distractors was taken as a measure of perceptual performance. The data demonstrate thatdiscrimination performance is superior when the discrimination stimulus is also the target for manual aiming; when the discrimination stimulus and pointing targetreferto differentobjects, performance deteriorates. Therefore, it is not possible to maintain attention on a stimulus for the purpose of discriminationwhiledirecting a movementtoa spatially separate object. The results argue for an obligatory coupling of (ventral) selection-for-perception and (dorsal) selection-for-action.