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Animals selectively filter and transform their sensory input, increasing the accuracy with which some stimuli are detected and effectively ignoring others. This filtering process, collectively referred to as “selective attention,” takes place at a variety of different levels in the nervous system. It was described in considerable detail by William James over a century ago (James, 1890/1950) and has been a principal focus of research in cognitive psychology for nearly 50 years (Parasuraman & Davies, 1984; Pashler, 1998; Richards, 1998). Investigations of selective attention have also been central to the study of animal cognition, where the process of attention has been considered to play an important role in a variety of behavioral paradigms (e.g.. Mackintosh, 1975; Riley & Roitblat, 1978). Most attention research, particularly in the realm of visual search, has been directed to the nature of the filtering processes applied to relatively simple, geometrical stimuli (reviewed in Humphreys & Bruce, 1989). Such stimuli can easily be varied along independent physical dimensions, allowing the relationship between targets and distracters to be controlled with considerable precision (e.g., Treisman & Gelade, 1980). However, the role of selective attention in determining responses to more complex visual stimuli, of the sort that organisms regularly deal with in the course of their normal behavioral routines, has been less explored. This neglect is of particular concern because, in the absence of artificial limitations on search time, simple geometrical stimuli do not place a sufficient demand on information processing capacity to demonstrate selective attention effects (Riley & Leith, 1976).
In addition to their use of simple geometrical stimuli, most attention studies in animals have used tasks with no clear, direct connection to the perceptual world of the species under study. There is, however, substantial literature suggesting that selective attention may play a significant role in nature, particularly in predator-prey interactions. A review of this literature, integrating it with more customary work on attentional psychology, raises questions of considerable interest to both psychologists and biologists. For psychologists, naturalistic experimental methods using more complex, multidimensional stimuli cast light on additional, unanticipated aspects of attentional processes in animals. For biologists, selective attention has long been considered a primary cognitive mechanism underlying the well-known tendency of visually searching predators to concentrate their attacks on relatively common prey types. As a consequence, the circumstances under which selective attention occurs and the magnitude of the enhancement in detection accuracy that results can have significant ecological and evolutionary effects. Our goal in this chapter, therefore, is to integrate data and hypotheses from both the ecological and the cognitive perspectives. When these two groups of literature are considered together, a variety of parallels emerge, parallels that lay the groundwork for a unified account of attentional phenomena in animals.