Scenes are so rich in information that the visual system cannot process all inputs simultaneously. Visual attention is the process that allows us to select the information that is relevant to our current behavior from the multiple inputs available at any given moment. Previous chapters have focused on the role of spatial and feature-based attention in selection. Here we show that attention can operate not only on the basis of locations and visual features but also by selecting an object as a whole. One way to study object-based attention is to require attention to a stimulus that is spatially superimposed on another, a situation which precludes spatial selection. Several studies have shown that it is possible to attend selectively to one of two transparent surfaces, finding that it is easier to divide attention between attributes of the same surface (e.g., direction and speed of motion) than between identical attributes for different surfaces. Moreover, attending to one feature causes other features of the same object to be processed efficiently. Electrophysiological and functional imaging findings show that the effects of surface-based attention are present from the early stages of visual processing. The units of attentional competition.
- Visual system