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Using Inattentional Blindness As an Operational Definition of Unattended: the Case of a Response±End Effect

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Using Inattentional Blindness As an Operational Definition of Unattended: the Case of a Response±End Effect VISUAL COGNITION, 2004, 11 6), 705±719 Using inattentional blindness as an operational definition of unattended: The case of a response±end effect Cathleen M. Moore, Alejandro Lleras, Marc Grosjean, and Mark T. Marrara Department of Psychology, Pennsylvania State University, USA Inattentional blindness IB), which is the lack of awareness of stimuli that appear in unattended regions of the visual field, can be used as an operational definition of unattended. Usingseparate online measures in combination with IB can be used to probe specific aspects of processing that are engaged by unattended stimuli. Pre- vious applications of this method have provided evidence that unattended stimuli can engage processes that lead to grouping-by-similarity Moore & Egeth, 1997), as well as processes involved in the perceptual completion of partially visible surfaces Moore, Grosjean, & Lleras, 2003). Here we applied this method to address the question of whether unattended stimuli can engage response±end processes. Specifically, we used a stimulus±response compatibility effect, the Simon effect e.g., Simon & Rudell, 1967), as an online measure of response selection. As assessed through this measure, unattended stimuli failed to engage response-selection processes. Inattentional blindness IB) is one of several recently documented illustrations of how dramatically people can fail to notice what happens around them. IB refers to the observation that salient but unexpected events, such as well above- threshold flashes of light, can go completely unnoticed if they occur in an unattended part of one's visual field e.g., Mack & Rock, 1998; see also change blindness, e.g., Rensink, O'Regan, & Clark, 1997; Simons, 2000b). Please address all correspondence to Cathleen Moore, Department of Psychology, Penn State University, University Park, PA 16802, USA. Email: [email protected] Portions of this work were presented at the 2001 meetingof the Vision Sciences Society in Sarasota, FL. Support was provided by NSF grant SBR-9728628. Alejandro Lleras is now at the University of Britisch Columbia in Vancouver, Canada; Marc Grosjean is now at the Max Planck Institute for Psychological Research in Munich, Germany; and Mark Marrara is now at the Meta- vante Corporation in Milwaukee, WI. We wish to thank Marvin Chun and two anonymous reviewers for helpful comments on a previous version of this paper. # 2004 Psychology Press Ltd http://www.tandf.co.uk/journals/pp/13506285.html DOI: 10.1080/13506280344000482 706 MOORE ET AL. Operationally, IB is assessed through an experimental method that was developed by Mack and Rock and their colleagues. They wished to contrast their approach with previous methods of probingunattended processing,such as visual search e.g., Treisman & Souther, 1985) and dual-task procedures e.g., Braun, 1993; Braun & Sagi, 1990) in which observers were aware of the potential relevance of the unattended stimuli. Awareness of the relevance of the supposedly unattended stimuli, argued Mack and Rock, might have caused those stimuli to be at least partially attended. Thus, the method that they developedÐ which we will refer to as the inattention methodÐwas aimed at probingthe processingof stimuli that were in the visual field, but that observers had no reason to suspect were relevant to anythingthat they were doing,and therefore should have been truly unattended. An intuitive example of what they sought in the laboratory is the pattern of the wallpaper behind a person with whom you are speaking. It is a large, above-threshold stimulus that is in your visual field, and yet it is not relevant to what you are doingat the time. You would be able to easily describe it if someone were to draw your attention to it. The question is, assumingthat your attention was not drawn to it, would you process it and could you describe it? The inattention method engages attentional processing using a difficult primary task. Mack and Rock 1998) asked observers to report whether the vertical or horizontal bar in a large central plus sign was longer. After about three trials of this task, another stimulus was presented alongwith the plus sign, somewhere in the display. For example, a bright filled-in square might appear somewhere in the upper-left quadrant of the display. Followingthat trial, the observer is asked if he/she noticed anythingelse in the display on that last trial, and is asked to make a forced-choice response regarding it, such as which of four quadrants it appeared in. Observers often report that they saw nothingother than the plus sign, and end up guessing at chance levels as to its location or other property. Once aware that additional stimuli may appear, however, observers are typically able to see and report on them quite well. This indicates that the stimuli were sufficiently salient to be perceived as longas they were attended, and therefore that the failure to perceive them when they were unattended could be attributed to the absence of attention. This entire pattern of results is the empirical indication of IB. Although there is a large set of stimuli that fail to support explicit report when they are unattended see Mack & Rock, 1998 for a review), other research suggests that substantial amounts of unreportable information pro- cessingof unattended stimuli does occur Kimchi & Razpurker-Apfeld, in press; Mack & Rock, 1998; Moore & Egeth, 1997; Moore et al., 2003; Most et al., 2001; Simons, 2000a). This processingwithout attention presumably provides the foundational representations out of which conscious perception emerges, and is therefore of considerable importance for theories of visual perception. OPERATIONAL DEFINITION OF UNATTENDED 707 In a recent paper, we suggested that IB can be turned around and used as a tool for studyinghow unattended stimuli are processed Moore et al., 2003). Specifically, the idea is to use IB as an operational definition of ``unattended''. Those stimuli to which observers are inattentionally blind are, by this definition, classified as ``unattended''. From there, one can use online measures to assess in what specific ways unattended information is processed, and in what ways it is not. By online measure, we mean a measure of a targeted process that is taken while that process is occurring, and therefore, while the stimuli in question are unattended. These online measures must be indirect, because probingobservers directly about some aspect of an unattended stimulus will necessarily draw their attention to the stimulus, makingit no longerunattended. The application of IB as an operational definition of unattended is useful because defining``unattended'' is often the main difficulty in studyinghow unattended stimuli are processed. As noted by Mack and Rock 1998; Mack, Tang, Tuma, Kahn, & Rock, 1992; Rock, Linnet, Grant, & Mack, 1992), pre- vious methods of assessingunattended processingare potentially problematic in that observers are often at least aware of the presence of the stimuli that were supposed to be unattended. ``Distractors'' in visual-search tasks, for example, which are often cited as beingprocessed preattentively, fall into this category e.g., Treisman, 1998; Treisman & Gormican, 1988; Wolfe, 1994). Flankers in tasks that seek to reveal the influence of unattended flankingstimuli on the processing of a central target do as well e.g., Eriksen & Eriksen, 1974; Eriksen & Hoffman, 1973). In other cases, the stimuli that are supposed to be unattended are task relevant, in that the procedure involves two tasks, the second of which concerns properties of the unattended stimuli e.g., Braun & Sagi, 1990). The possibility that the stimuli that are supposed to be unattended in these methods are at least partially attended can reduce the strength of the conclusions that can be drawn concerningthe processingof unattended stimuli. For this reason, establishingan operationally defined domain of ``unattended'' should be lib- erating. We suggest here and elsewhere Moore et al., 2003) that IB is a good candidate measure for operationally constrainingthe definition of ``unat- tended''. There are two steps involved in the approach proposed here. First an online measure of the process that one wishes to assess must be chosen or developed. A balance of criteria for this measure must be met. The measure must reflect the targeted processes, but it also must be one that will support IB. In other words, the stimuli that are required for the online measure cannot themselves be likely to capture attention. This follows because the basis of the approach is that evidence of IB to the stimuli will define the stimuli as unattended, and only then can the question of whether that process is engaged by unattended stimuli be addressed by lookingat the online measure. In Moore et al. 2003), we applied this approach to the perceptual comple- tion of partial surfaces. We first developed an online measure of surface com- 708 MOORE ET AL. pletion. Observers reported as quickly as possible whether the central line was dashed or solid see insert in Figure 1). In some displays, pacmen in the background of the display were randomly oriented such that no particular completion pattern was supported Figure 1A). In other displays, they were aligned so that modal completion into rectangles was supported Figures 1B and 1C). When the rectangles were aligned with the gaps in a dashed line, they would in turn support the amodal completion of the dashed line behind the modally completed rectangles into a representation of a solid line Figure 1B), thereby slowingresponses to report ``dashed'' on these trials. The slow- ingwas taken as an indication that both modal completion of the rectangles and amodal completion of the line occurred. Havingestablished an online measure of surface completion, the next step was to use that measure in the context of the inattention method. The online measure indicated that both modal and amodal completion occurred. Despite this, when observers were probed regarding their awareness of the surfaces themselves, using the inat- tention method, they showed IB to them.
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