Attentional modulation along the ventral pathway of the cortical visual system of primates consists in enhanced representation of the retinal input at a specific location in space, or of objects located anywhere in the visual field which possess a critical feature. Crucially, selective attention mechanisms also allow the visual system to resolve competition among multiple objects in a cluttered scene in favor of the one that is relevant for the current behavior. Finally, selective attention affects both the spontaneous activity of neurons as well as their visually driven activity, and it does so not only by modulating the rate of firing of individual neurons, but also by modulating the degree of synchronized firing within the critical neuronal populations.