Interaction between bottom-up saliency and top-down control: how saliency maps are created in the human brain.

Whether an object captures our attention depends on its bottom-up salience, that is, how different it is compared with its neighbors, and top-down control, that is, our current inner goals. At which neuronal stage they interact to guide behavior is still unknown. In a functional magnetic resonance imaging study, we found evidence for a hierarchy of saliency maps in human early visual cortex (V1 to hV4) and identified where bottom-up saliency interacts with top-down control: V1 represented pure bottom-up signals, V2 was only responsive to top-down modulations, and in hV4 bottom-up saliency and top-down control converged. Two distinct cerebral networks exerted top-down control: distractor suppression engaged the left intraparietal sulcus, while target enhancement involved the frontal eye field and lateral occipital cortex. Hence, attentional selection is implemented in integrated maps in visual cortex, which provide precise topographic information about target-distractor locations thus allowing for successful visual search.