The effects of abrupt onset of 2-D and 3-D distractors on prehension movements

The notion that attention can be captured by the onset of new perceptual objects has been well documented in a series of experiments based on visual search tasks (Gibson, 1996a, 1996b; Yantis & Jonides, 1984, 1996). In particular, it has been demonstrated that visual onsets capture attention because they coincide with the appearance of a perceptual object and not because of the sudden increment in luminosity (Yantis & Jonides, 1984). Yantis and Jonides (1984) suggest that when a new object appears in the visual field it is necessary to create a new perceptual representation, and attention is typically directed toward it (Jonides & Yantis, 1988; Yantis & Jonides, 1996). As such, the new object may act as a nonspecific attentional distractor. Remington, Johnston, and Yantis (1992) demonstrated that response time to a letter target appearing in one of four boxes was increased if the target was preceded by distinct abrupt-onset visual stimuli flashed briefly in another box, in all boxes, or at fixation. This suggests that attention is captured involuntarily by abrupt onset. In the present study, attention is not directly manipulated; however, it is conceivable to infer that the abrupt onset of a visual stimulus produces attentional capture. Instead of using typical laboratorygenerated stimuli (e.g., colored bars, Xs and Os) that bear little resemblance to the scenic objects that draw attentionduring naturally occurring tasks, we use a natural reach-to-grasp task performed toward real three-dimensional(3-D) objects (Jeannerod, 1981) to investigate attentional capture by abrupt onsets. The hypothesis that the abrupt illumination of a new perceptual object captures attention and can influence a planned overt motor action is tested. The general idea is that attention can access several processing modes, therefore several types of representations may operate simultaneously. For example, representations associated with object-oriented actions have distinct properties that make them distinct from those of other representations like object identification (Goodale & Milner, 1992). Consequently, it is hypothesized that not only a perceptual but also a motor representation for the “distracting” object is created, attention is directed toward it, and perceptuomotor aspects of a new “object file” are opened. The prediction is that, at this point, both target and distractor objects can trigger competing reach-to-grasp programs, and the attentionally modulated resolution of this is played out in the kinematics of the reach to the target (Bonfiglioli & Castiello,1998;Castiello,1996; Chieffi, Gentilucci, Allport, Sasso, & Rizzolatti, 1993; Howard & Tipper, 1997; Jackson, Jackson, & Rosicky, 1995; Tipper, Howard, & Jackson, 1997). The link between selective attentional mechanisms and the control of action has already been observed in an experiment that forced a degree of covert attention to the distractor objects (see Castiello, 1996; Experiments 5 and 6). Subjects reached to grasp a target while having to count the number of times that a distractor object was illuminated by a spotlight.Under these circumstances, the characteristics of the distractor influenced the kinematicsof the reach-tograsp movement. Specifically, the amplitude of peak grip aperture—that is, the distance between the index finger and the thumb—was influencedby the lateral distractor object. The amplitude of peak grip aperture for a target This research was sponsored by the Australian Research Council. I thank T. Sanocki, H. A. Sedgwick, K. Shapiro, and an anonymous referee for valuable comments and suggestions for improving the quality of the article. Correspondence concerning this article should be addressed to U. Castiello, Department of Psychology, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, England (e-mail: u.castiello@rhul.ac.uk). The effects of abrupt onset of 2-D and 3-D distractors on prehension movements