Visual Marking: Using Time as Well as Space in Visual Selection: Derrick G.Watson, Glyn W.Humphreys and Christian N.L. Olivers

Abstract

One of the main functions of the visual system is to allow an internal representation of the external world to be developed in order for us to interact efficiently and successfully with our environment. However, the visual world typically contains vast amounts of information, far more than can possibly be processed by our limited sensory and cognitive capabilities. Such limitations are readily demonstrated when we fail to detect even large changes that occur between sequentially presented visual scenes or even in real-world interactions (Simons, 1996; Simons & Levin, 1997; 1998) or when we fail to notice new stimuli while attending to other stimuli (Mack & Rock, 1998). Even if a stimulus is attended, the details of its visual representation may fade rapidly, perhaps even to a level no greater than that before attention was applied (Wolfe, Klempen, & Dahlen, 2000). Indeed, visual attention may be required to become conscious of even the most simple of features (Joseph, Chun & Nakayama, 1997; see also Mack, Tang, Tuma, Kahn, & Rock, 1992; Rock, Linnett, Grant, & Mack, 1992). We are thus greatly limited in the number of objects that we can attend to, process, or link to actions at any particular moment in time (e.g., Allport, 1987; Duncan, 1980). Fortunately, much of the information represented in the visual array may often beirrelevant to our particular current or future needs. However, it is clearly of great importance to be able to control effectively and prioritize the types of stimuli that receive preferential processing depending on our current behavioral needs. Consider, for instance, the predator’s goal of detecting its prey. In this situation, the predator needs to detect the prey as soon as it appears from a background of other largely irrelevant items. The irrelevant items need to have little impact for selection to be efficient. Likewise, not all the visual information available to an air traffic controller or a pilot may need to be processed. Traditionally, theories of visual attention have emphasized selection through space. That is, attention is said to act like a spotlight or a zoom lens (e.g., Eriksen & St. James, 1986; Posner, 1980), with objects falling within the “illuminated” area receiving the greatest processing. Indeed, Neisser (1976) argued that, if picking apples from a tree, you simply “select” the one that you want without needing a mechanism to suppress other apples, to prevent them from being picked. In contrast to selection based on spatial parameters as previously described, here we consider how the visual system can also use time to prioritize selection.