OBJECT-BASED ATTENTION IN THE PRIMARY VISUAL-CORTEX OF THE MACAQUE MONKEY

Typical natural visual scenes contain many objects, which need to be s egregated from each other and from the background. Present theories su bdivide the processes responsible for this segregation into a pre-atte ntive and attentive system(1,2). The pre-attentive system segregates i mage regions that 'pop out' rapidly and in parallel across the visual field. In the primary visual cortex, responses to pre-attentively sele cted image regions are enhanced(3-5). When objects do not segregate au tomatically from the rest of the image, the time-consuming attentive s ystem is recruited. Here we investigate whether attentive selection is also associated with a modulation of firing rates in area V1 of the b rain in monkeys trained to perform a curve-tracing task(6,7). Neuronal responses to the various segments of a target curve were simultaneous ly enhanced relative to responses evoked by a distracter curve, even i f the two curves crossed each other. This indicates that object-based attention is associated with a response enhancement at the earliest le vel of the visual cortical processing hierarchy.