Feature-based attention modulates feedforward visual processing

It is widely believed that attention selects locations at an earlier stage than it selects nonspatial features, but this has been tested only under conditions of minimal competition. We found that, when competition was increased, color-based attention was able to influence the feedforward flow of information in humans within 100 ms of stimulus onset, even for stimuli presented at unattended locations. Thus, color-based attention can operate as early as, and independently from, spatial attention.