The effect of novel distractors on performance in focused attention tasks: A cognitive-psychophysiological approach

GERSHON BEN-SHAKHAR 0 1 2 3 0 Hebrew University of Jerusalem , Jerusalem , Israel and The Open University of Israel , Raanana, Israel 1 EINAT SEQUERRA and ASHER COHEN Hebrew University of Jerusalem , Jerusalem, Israel 2 NURIT GRONAU Harvard Medical School , Charlestown, Massachusetts 3 This research was supported by the Israel Foundations Trustees. We thank Tram Neill , Jan Theeuwes, and Robert Rauschenberger for help- ful comments, and Ori Cohen and Avia Munchik for their help in data to N. Gronau, Martinos Center for Biomedical Imaging at MGH, Har- vard Medical School , 149 Thirteenth St., Room 2301, Charlestown, MA 02129 ( In the present study, we examined whether or not novel stimuli affect performance in a focused attention task. Participants responded to a central target while an irrelevant distractor in the visual display was occasionally changed. In Experiment 1, both target and distractor were presented centrally within the focus of attention. In Experiment 2, a central target was presented along with an irrelevant distractor at a peripheral location, outside the focus of attention. Novel distractors were associated with longer latencies and enhanced orienting responses (as measured by skin conductance responses) only when presented at an attended location. In contrast, as is demonstrated in Experiment 3, the same peripheral novel distractors interfered with task performance when they possessed task-relevant information. These results indicate that there is a fundamental difference between novel stimuli and task-relevant stimuli. Whereas the former exert influence only within the focus of attention, the latter affect performance even when positioned in an unattended location. Our findings have important implications for the operation of visual attention. - Visual tasks often involve presentation of both target and distractor stimuli, requiring selection of the targets and filtering out of the distractors. Ample evidence suggests that visual attention mediates this selection by focusing either on a region (Posner, 1980) or on an object (Duncan, 1984) in the visual scene. However, selection by visual attention is not perfect, and numerous studies have demonstrated that distractors may affect performance even in tasks in which participants focus their attention on the targets location ahead of time (e.g., Eriksen & Eriksen, 1974; Stroop, 1935). The boundary conditions for interference in focused attention tasks have been extensively investigated because they may shed light on the processes underlying the selective attention mechanism. One prominent example of this approach is the examination of the influence of distractors on performance when these distractors are presented either within or outside the focus of attention. In this study, we examine whether novel stimuli that are irrelevant for the task interfere with focused attention tasks when they are positioned within and outside the main focus of attention.1 It is interesting to compare the influence of distractors appearing in attended and unattended locations because much evidence suggests that visual attention acts as a gating mechanism (see, e.g., LaBerge, 1983). That is, stimuli positioned inside the focus of attention gain access to higher level processes dealing with the task at hand. Consequently, distractors presented within the focus of attention allow one to observe whether or not they are sufficiently salient to interfere with task-related processes. On the other hand, distractors presented outside the focus of attention will affect performance only to the extent that these stimuli can interfere with attentional processes occurring at the target location. Thus, finding out which types of distractors affect performance when positioned in an unattended location is crucial for understanding the nature of the attentional mechanism. It is well established that distractors carrying task-relevant information (henceforth, task-relevant distractors) affect performance whether they are inside or outside the attentional focus. In the classic Stroop (1935) paradigm, for example, words denoting names of colors affect responses in a color naming task, lengthening or facilitating reaction times (RTs) to target colors. Importantly, this effect is observed both when the distracting words appear within the focus of visual attention (integrated with the colors, as in the typical Stroop paradigm) and when they are positioned outside the main focus of attention (spatially separated from the colors; see, e.g., Kahneman & Henik, 1981). Similarly, taskrelevant distractors located on either side of a central target affect responses to the target in the well studied flanker task (Cohen & Shoup, 1997; Eriksen & Eriksen, 1974).2 The effects of other salient distractors on attentional processes are less clear. Several studies, dating back to Moray (1959), focused on the impact of personally significant but task-irrelevant distractors (e.g., the participants own name) on task performance. These studies produced inconclusive results (e.g., Bundesen, Kyllingsbk, Houmann, & Jensen, 1997; Mack & Rock, 1998; Wolford & Morrison, 1980). As Gronau, Cohen, and Ben-Shakhar (2003) pointed out, this state of affairs may have been caused by a lack of proper control of visual attention. Gronau et al., using a focused attention task in which participants attention was controlled, showed that personally significant stimuli affect performance and elicit an orienting response (ORi.e., an increase in skin conductance) when presented within but not outside the focus of attention. Indeed, the effect of personally significant distractors within the focus of attention was similar in magnitude to that of task-relevant distractors, implying that these two types of distractors are equally salient. Nevertheless, only the latter affected performance when located outside the attentional focus. These findings imply that attentional processes are not linked to or affected by all salient representations but only by those associated in some way with task demands. Gronau et al. speculated that attention may be uniquely associated with representations in transient stores (e.g., working memory) that are activated during task performance. However, the personally significant stimuli used by Gronau et al. (2003) might not be generalized to all types of salient distractors. In particular, the saliency of ones own name is derived by semantic analysis of the stimulus. It is possible that salient changes in the physical environment that do not require high-level semantic analysis would affect performance regardless of their relevance for the task. If so, attention may also be linked to and affected by salient representations that are not associated with task demands. In the present article, we address this issue by examining whether novel stimuli affect task performance when presented both within and outside the focus of attention. By novelty, we mean any nota (...truncated)