Academic journal article Perception and Psychophysics

Onset but Not Offset of Irrelevant Motion Disrupts Inhibition of Return

Academic journal article Perception and Psychophysics

Onset but Not Offset of Irrelevant Motion Disrupts Inhibition of Return

Article excerpt

In seven experiments, subjects were slower to detect targets in cued static objects than in uncued static objects, revealing inhibition of return (IOR). This occurred regardless of the presence or absence of continuous motion of other, task-irrelevant objects in the display. However, if the motion of the irrelevant objects began during the interval between cue and target, the amount of IOR was considerably reduced. Offset of motion during the cue-target interval had no effect. Implications for IOR, object perception, and attentional capture are discussed.

Inhibition of return (IOR) refers to a relative slowness to respond to stimuli at recently attended locations (Posner & Cohen, 1984). IOR is thought to permit efficient visual searches in complex environments because it biases a search toward fresh sources of input. Consistent with this view are findings that indicate that IOR operates in an object-based reference frame. For example, Tipper, Driver, and Weaver (1991) presented two objects on an imaginary circle centered at fixation. The objects both moved partway around the circle, during which time one of them was cued by flickering. Subjects were slower to detect a subsequent target presented in the cued object (in comparison with the uncued one) even though the object had since moved to a new location. Thus, IOR appears to include an object-based component that permits inhibition of an attended object even after it moves. Subjects are also slower to detect stimuli at the original location of the cue even after the cued object has left, revealing an additional location-based component to the inhibition (Tipper et al., 1991). Several others have provided evidence of both the object- and location-based components of IOR (e.g., Abrams & Dobkin, 1994; Abrams & Pratt, 2000; Jordan & Tipper, 1998; McCrae & Abrams, 2001; Tipper, Weaver, Jerreat, & Burak, 1994), although there are also some special situations in which the object-based component has not been observed (Abrams & Dobkin, 1994; Abrams & Pratt, 2000).

Despite the ecological arguments made in support of IOR, most of what is known about it comes from paradigms in which participants viewed static stimuli or from paradigms such as the one just described, in which the few relevant objects in the display moved a short distance. Such situations are artificial and not typical of real-world scenes, in which many different kinds of motion are possible and in which motion through the environment may cause images of many objects to move across the retina. To examine IOR in dynamic scenes, we recently studied what happens when a cued object moves away from its initial location but then returns to it (Christ, McCrae, & Abrams, 2002). Quite surprisingly, we found that the IOR was almost completely eliminated even though both objectbased and location-based components of inhibition might be expected to be operating when a cued object returns to its initial location. It is significant that our results showed that dynamic scenes may reveal properties of IOR that differ from those present in static scenes.

In the present research, we sought to extend our ear lier investigation of IOR in dynamic scenes by examining situations in which the motion involves objects that are not directly relevant to the subject's task. Such a situation may be typical of many real-world searches in which the object of primary interest may be stationary or, if moving and fixated, may be the least likely to move relative to the retina. Under conditions such as these, little is known about the role that IOR might play in search. In the experiments that follow, we examine IOR under conditions in which irrelevant objects in the display undergo one of several different types of motion or do not move at all. The results reveal that some types of motion are not disruptive at all, whereas other types of motion can dramatically affect the magnitude of IOR.

The present study also provides an opportunity to examine the possibility that some types of motion have a qualitatively different impact on attention than do others (Franconeri & Simons, 2003; but see Abrams & Christ, 2005). …

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