Visual Attention

Visual attention is the factor controlling the selective access and integration of visual information. INTRODUCTION Although much of vision appears to be effortless and all-encompassing, nevertheless there are limits to what it can do. For example, consider air traffic control, where it is imperative to keep track of all moving items in a display (corresponding to the airplanes in an airspace). If only a single item is present, it can generally be tracked without problem. It is also possible to track four or five items simultaneously, although some effort is needed to do so. However, for 20 or 30 items, even a maximal effort will not suffice, and the task must be shared among several controllers. What appears to be happening in such cases is that visual perception is constrained by a consciously controlled factor within the observer ± a factor that enables certain types of processing to take place, but which is limited in the extent to which it can be applied. This factor is termed visual attention. Interestingly, although most observers immediately know what to do when asked tòpay atten-tion' to a stimulus, it has been rather difficult to give this an objective characterization. Indeed, until recently there was no general consensus on the basic function of attention, and at various times it was associated with such things as clarity of perception , intensity of perception, consciousness, and selection. SELECTION During the past few decades, considerable progress has been achieved by focusing on selection as the basic function of visual attention. Two types of selection are of particular importance. The first is selective access (i.e., allowing only certain parts or properties to be sent on to later processes). It was originally believed that selective access protected processors at higher levels from being overwhelmed by too much information. However, more recent research has tended to view selective access as a way to delimit control of various actions (e.g., focusing on the locations of items that are to be grasped). The second type of selection is selective integration (i.e., combining selected parts or properties into structures that then form the basis of further processing). For example, three adjoining lines could be combined into a complete figure. This figure (and not the lines themselves) might then provide the basis for subsequent control of grasping. It was initially believed that such integration had to be selective in order to make good use …