Object-based attention

Object-based attention refers to the relationship between an ‘object’ representation and a person’s visually stimulated, selective attention, as opposed to a relationship involving either a spatial or a feature representation; although these types of selective attention are not necessarily mutually exclusive. Research into object-based attention suggests that attention improves the quality of the sensory representation of a selected object, and results in the enhanced processing of that object’s features. Object-based attention refers to the relationship between an ‘object’ representation and a person’s visually stimulated, selective attention, as opposed to a relationship involving either a spatial or a feature representation; although these types of selective attention are not necessarily mutually exclusive. Research into object-based attention suggests that attention improves the quality of the sensory representation of a selected object, and results in the enhanced processing of that object’s features. The concept of an ‘object’, apropos object-based attention, entails more than a physical thing that can be seen and touched. It includes a perceptual unit or group, namely, elements in a visual field (stimuli) organised coherently by Gestalt factors such as collinearity, closure, and symmetry. Early researchers initially postulated that space-based considerations were the driving force behind visual attention; however, it became evident that their views needed to include the “thing” that attention selects. This object-based focus was extended, from Kahneman & Henik’s leading question: “If attention selects a stimulus, what is the stimulus it selects?” and their consideration that attention might also be object-driven, through Duncan’s influential and explicit delineation between space-based and object-based theories of attention, to the current status presented in this article.:1 A classic example of a cuing study undertaken to evaluate object-based attention was that of Egly, Driver, and Rafal. Their results demonstrated that it was quicker to detect a target that was located on a cued object than it was to locate the target when it was the same distance away, but on an uncued object. Pertinently, Duncans’s:2 efforts were later verified by Vecera & Farah’s findings that shape discrimination tasks are dependent upon object-based representations, which in turn result in object-based attentional effects. The contribution of object-based attentional guidance to visual processing is widely accepted, with both object-based and space-based perceptual representations now included in recent models of visual attentional selection. When considering the nature and effects of object-based attention, three research theories are commonly mentioned; these are presented below. Consideration is then given to the enhancing effect of object-based attention on memory, and its inhibitory effect during certain kinds of visual search. The first theory posits that visually perceived objects affect the distribution of conscious and unconscious attention. Therefore, consciously attending to one aspect of an object automatically facilitates the processing of other aspects of the same object (including those currently task-irrelevant),:1 whether in terms of accuracy or response times. When a visual search involves locating two features, it is more efficient when both of the features occur in the same object, as opposed to two features separated in two different objects. Furthermore, that when re-viewing a previously attended object, recognition is faster when there is continuity between the representations (form, colour, orientation, etc.) of that object and the previewed one. The second theory asserts that object-based attention can shift quicker within an object than between objects. Egly and colleagues provided evidence for an object-based component of such visual orienting in a cued reaction time task involving both normal participants and parietal-damaged patients.:1 As an extension, research has indicated that when looking for a target among objects, there is also a preference to make eye-shifts within the same object, rather than between objects. The third theory contends that there is greater interference of object-based attention when any flanking distractors (e.g., visual scene crowding or noise) are present. Particularly, if these distractors belong to the same object or object-group as that being attended (noise similar), as opposed to coming from different objects (noise dissimilar)—irrespective of the distinguishing characteristics of the objects themselves (e.g., colour, motion direction, shape, orientation). An influencing element is that an object-like representation can engage attention even when it is not the intended target of a visual search. Therefore, an important consideration is that the perceptual resemblance between distractors and a target object influences the efficiency of visual search; increases in similarity among the distractors, increases search efficiency. Similarly, visual search efficiency increases the less similar the target is to the distractors.