SELECTIVE DORSAL AND VENTRAL PROCESSING - EVIDENCE FOR A COMMON ATTENTIONAL MECHANISM IN REACHING AND PERCEPTION

The primate visual system can be divided into a ventral stream for per ception and recognition and a dorsal stream for computing spatial info rmation for motor action. How are selection mechanisms in both process ing streams coordinated? We recently demonstrated that selection-for-p erception 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-ta sk paradigm required the preparation of a reaching movement to a cued item in a letter string. Simultaneously, the ability to discriminate b etween the symbols ''E'' and ''There Exists'' presented tachistoscopic ally within the surrounding distracters was taken as a measure of perc eptual performance. The data demonstrate that discrimination performan ce is superior when the discrimination stimulus is also the target for manual aiming; when the discrimination stimulus and pointing target r efer to different objects, performance deteriorates. Therefore, it is not possible to maintain attention on a stimulus for the purpose of di scrimination while directing a movement to a spatially separate object . The results argue for an obligatory coupling of (ventral) selection- for-perception and (dorsal) selection-for-action.