Combined effects of spatial and feature-based attention on responses of V4 neurons.

Attention is thought to be controlled by a specialized fronto-parietal network that modulates the responses of neurons in sensory and association cortex. However, the principles by which this network affects the responses of these sensory and association neurons remains unknown. In particular, it remains unclear whether different forms of attention, such as spatial and feature-based attention, independently modulate responses of single neurons. We recorded responses of single V4 neurons in a task that controls both forms of attention independently. We find that the combined effects of spatial and feature-based attention can be described as the sum of independent processes with a small super-additive interaction term. This pattern of effects demonstrates that the spatial and feature-based aspects of the attentional control system can independently affect responses of single neurons. These results are consistent with the idea that spatial and feature-based attention are controlled by distinct neural substrates whose effects combine synergistically to influence responses of visual neurons.