Object-Based Attentional Selection is Affected by Visual Search Strategy

摘要

Object-based selective attention is often assumed to spread automatically throughout any object to which attention is cued. However, Shomstein and Yantis (2002, 2004) reported that object-based attentional modulation arises only when the target location is uncertain, suggesting that attention is deployed only to behaviorally relevant locations on the objects. In a previous presentation (VSS, 2006) we extended these findings by showing that contingent attentional capture (Folk et al, 1992) is object-based only when target location is uncertain. Here we examined the role of visual search strategy in object-based attention. Displays contained two rectangles with 5 RSVP streams (one at fixation and one at each end of the two objects). The four peripheral streams contained all gray letters and the central stream was either all gray (Experiment 1) or multicolored (Experiment 2). Subjects were aware that the central stream contained a red target letter (or green for half the subjects) on each trial, which they were to identify. One or two frames prior to target onset, a target-colored or nontarget-colored distracter could appear in one of the peripheral RSVP streams (same or different rectangle). Robust contingent capture was observed in both experiments, but its magnitude differed for distracters on the same versus different objects only in Experiment 1. Furthermore, performance on nontarget-colored distracter trials suggested that subjects used a temporal Singleton Detection Mode (SDM) to detect targets in Experiment 1 and Feature Search Mode (FSM) in Experiment 2 (Bacon & Egeth, 1994). Because FSM requires a more specific definition of the target-defining feature than does SDM, the present data show that uncertainty in the target-defining feature (here, during SDM) can evoke object-based attentional modulation, even when target location is certain. Thus, a more general principle of target uncertainty may guide the allocation of attention to objects.