Psychological Research DOI 10.1007/s00426-014-0599-8
ORIGINAL ARTICLE
Attentional capture by completely task-irrelevant faces Shiori Sato • Jun I. Kawahara
Received: 14 January 2014 / Accepted: 9 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract The present study investigated whether faces capture attention regardless of attentional set. The presentation of a face as a distractor during a visual search has been shown to impair performance relative to when the face was absent, implying that faces automatically attract attention. If attentional control is contingent on the observer’s current goal, faces should not capture attention when they are irrelevant to the observer’s attentional set. Previous studies demonstrating face-induced attentional capture used faces that were relevant to the task. Thus, a task in which faces were completely irrelevant to the observer’s set was created. Participants identified a target letter among heterogeneously colored non-targets while ignoring a peripheral facial image that appeared as a brief distractor. No face-specific capture was observed when the targetdistractor stimulus onset asynchrony (SOA) was long (Experiment 1). When the SOA was shortened, attentional capture by irrelevant faces was observed (Experiment 2). Experiment 3 extended this finding to all conditions, regardless of the attractiveness of faces. No such capture effect was found in Experiment 4 with inverted-face distractors. These results indicate that completely task-irrelevant faces break through top-down attentional set given a brief distractor-target SOA.
S. Sato J. I. Kawahara (&) Department of Psychology, Chukyo University, 101-2 Yagoto, Showa, Nagoya 466-8666, Japan e-mail: [email protected] J. I. Kawahara National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
Introduction Of the various objects and events in our visual environment, it is reasonable to assume that our attention shifts to extremely salient stimuli (e.g., an approaching fire engine while driving). This assumption is supported by considerable evidence that salient stimuli are quickly and accurately perceived, demonstrating that visual attention is oriented to the abrupt onset of salient objects or events regardless of observers’ current behavioral goals (Franconeri, Hollingworth, & Simons, 2005; von Mu¨hlenen & Lleras, 2007; Schreij, Owens, & Theeuwes, 2008). Similarly, the presence of such salient stimuli (Kawahara, Yanase, & Kitazaki, 2012; Van der Stigchel et al., 2009) impairs performance when they act as distractors. It is also widely accepted that visual attention is oriented toward objects of great biological and social significance. For example, human faces expressing a negative emotion are detected more efficiently than faces expressing a neutral emotion (Eastwood, Smilek, & Merikle, 2001). Furthermore, the mere presence of a distractor face, regardless of expression, has been shown to delay visual search relative to cases in which no distractor face was presented, implying that faces summon attention when they are presented within (Langton, Law, Burton, & Schweinberger, 2008) or outside of (Lavie, Ro, & Russell, 2003) a visual search display. A computational model better predicted voluntary eye gaze purportedly preceded by attentional shift when face detection was incorporated than when no such components were included (Cerf, Harel, Einha¨user, & Koch, 2008). Moreover, Theeuwes & Van der Stigchel (2006) have provided strong evidence for stimulus-driven orienting toward task-irrelevant faces by demonstrating inhibition of return (delayed responding with a saccade) to a location that previously contained a face.
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These results suggest that faces are processed automatically. However, it is unclear whether these results mean that faces capture attention regardless of observers’ current behavioral goals. Given recent findings that attentional capture can be exogenous, it is important to determine whether stimulus-driven orienting of attention can be modulated by endogenous, top-down control (Einha¨user, Rutisha¨user, & Koch, 2008; Wyble, Folk, & Potter, 2013). However, the aforementioned studies implying automatic and necessary attentional capture by faces are inconsistent with evidence for intentional flexible attentional control. Specifically, researchers have shown that attentional capture by irrelevant distractors can be eliminated when a task is designed to prompt observers to adopt an attentional set that involves searching for a particular color (Ansorge & Heumann, 2003; Chen & Mordkoff, 2007; Folk & Remington, 1998; Folk, Remington, & Johnston, 1992; Lien, Ruthruff, Goodin, & Remington, 2008; Pratt & McAuliffe, 2002). This type of attentional control is sufficiently powerful to override stimulus-driven capture (Bacon & Egeth, 1994; Leber & Egeth, 2006). The purpose of the present study was to reconcile this apparent inconsistency regarding the attentional capture elicited by face distractors. If the visual system were, in general, capable of configuring top-down attentional control for visual searches involving not only simple features such as colors and shapes, but also more complex visual patterns, attentional capture by faces should be eliminated owing to flexible attentional control settings. However, attentional capture has been shown to be elicited by task-irrelevant faces (e.g., Langton et al., 2008). Nonetheless, we argue that it seems premature to conclude that faces are endowed with a special ability to capture attention. Indeed, careful examination of previous studies supporting automatic attentional capture by faces revealed that such studies were not designed to examine whether entirely task-irrelevant faces can capture attention. For example, studies in which observers’ primary goal was to search for faces do not tell us whether the visual system can exclude task-irrelevant face distractors (Eastwood et al., 2001) because, by definition, faces were targets (i.e., task relevant) in those circumstances. Thus, it is reasonable to assume that a face singleton would be processed and would affect visual performance. The same concern applies to studies that have supposedly demonstrated automatic attentional capture by faces by showing that the reaction times for visual searches were longer when a face distractor was included in a search array than when no such item was included (e.g., Langton et al., 2008; Ro, Russell, & Lavie, 2001). Face distractors shared similar features (size and color) with the search targets themselves. Moreover, most face distractors in those studies were presented at potential target locations
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(e.g., Theeuwes & Van der Stigchel, 2006; Langton et al., 2008; Bindemann, Burton, Langton, Schweinberger, & Doherty, 2007). Therefore, faces were a part of observers’ attentional set in these previous studies, and it remains unclear whether faces can break through such an attentional set when they are entirely task irrelevant. The present study examined this question. To introduce faces as entirely task-irrelevant distractors, the features that differentiate targets from non-target filler items should not overlap with those that define the distractor. To fulfill this requirement, we adopted an established paradigm that has been used to measure attentional capture by task-irrelevant distractors (Folk, Leber, & Egeth, 2002). This task is similar to those used in attentional blink studies (Shapiro et al., 1997) and rests on the widespread assumption that limited attentional resources are associated with deficits in cognitive processing. Specifically, in the original study conducted by Folk et al. (2002), observers searched for a target letter, as defined by a color (i.e., green), embedded in a rapid central stream of non-target heterogeneously colored letters. A task-irrelevant distractor (e.g., a pound sign) was briefly presented outside the current spatial focus of attention (above, below, to the left, or to the right of the central letter stream) before the target appeared. The researchers found no differences between irrelevant distractors and no distractors and sometimes these authors observed slightly impaired target identification with irrelevant color distractors as compared to no distractors. However, identification accuracy decreased when a distractor shared a feature with the target (green), implying that attentional capture is contingent on observers’ goals. This deficit has been attributed to the temporary unavailability of attentional resources that are diverted to the distractor. In the present study, the facial image that served as the distractor was displayed outside the central letter stream. Thus, we ensured that the faces were completely task irrelevant. We reasoned that if the visual processing of faces were automatic and if the faces capture attention regardless of observers’ behavioral goals, identification of a target letter should be more impaired when a distractor face was presented at an entirely task-irrelevant peripheral location relative to when no such distractor was presented or to when a control (scrambled) facial image was presented.
Experiment 1 The present experiment compared the accuracy of targetletter identification under a condition in which a distractor face was presented briefly before the onset of the target (face condition) and under the following three control conditions: the face-control condition, in which a
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scrambled facial image was presented; the frame condition, in which a rectangular frame was presented; and the nodistractor condition. We predicted that if the abrupt onset of visual items captures attention, accurate target identification would be more impaired under the three distractor conditions than under the no-distractor condition. More importantly, if the onset of a face captures attention, observers would be less accurate under the face condition than under the face-control condition. Such a pattern of results would mean that faces have a special ability to capture attention. In contrast, if attentional capture were governed by observers’ set, no differences in the rates of accurate identification would be observed under the face and the face-control conditions. Method Participants Nineteen undergraduates and graduate students (7 males and 12 females, aged 18 and 22 years, M = 20.0 years recruited from the Chukyo University subject pool for this and the following experiments) with normal or corrected-to-normal vision were recruited and paid for their participation. Stimuli and apparatus The stimuli consisted of a rapid central stream of 20 heterogeneously colored (red, green, yellow, purple, or light
blue) uppercase letters (Fig. 1). The letters subtended a visual angle of *1° in height at a viewing distance of *45 cm and were displayed on a black background. Stimuli were generated by MATLAB 2010 with the Psychophysics Toolbox (Brainard, 1997; Pelli, 1997) and displayed at the center of a CRT computer screen (1,024 9 768 pixels driven at a 60-Hz refresh rate). The distractor faces were digitized from university yearbooks and saved as color bitmap images. Of the 1,932 female images originally scanned, we identified the 80 most attractive pictures based on ratings obtained from 31 raters who were not involved in the present study. In Experiment 1, we used enlarged versions of the same set of images (472 9 354 pixels, subtending 8.9° in height and 12.3° in width). The images used under the face-control condition were Fourier-scrambled versions of the same facial images (Halit, Csibra, Volein, & Johnson, 2004). These control images were created by randomizing the phase spectra of the faces while keeping the amplitude and color spectra constant. Specifically a two-dimensional fast Fourier transform was applied to the RGB color components of the original images. The phase on each frequency was replaced by a random value between -p and p (uniform distribution). The image was then reconverted by an inverse Fourier transform. The colors of the letters were chosen so that participants would adopt the feature-search mode: the target was red for odd-numbered participants, and the nontarget was green, yellow, purple, or light blue. Red was replaced with green for even-numbered participants. Each
Fig. 1 A schematic diagram of the stimulus sequence in Experiment 1. Participants were required to identify a red letter (target) embedded in a rapid sequence of non-target letters in homogenous colors (green, yellow, purple, and light blue). The SOA of the central sequence was 100 ms and a distractor frame (if any) appeared 200 ms before the target. A facial image could appear in one of the distractor frame (the image presented here with permission of Shiori Sato) (color figure online)
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Procedure and design
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At the beginning of each trial, a fixation cross was displayed at the center of the screen. Observers initiated each trial by pressing the spacebar. After a delay of 500 ms, a rapid stream of letters was presented. The stream consisted of 20 different non-target letters and a target (a green letter for half of the randomly assigned observers and a red one for the other half). The number of non-targets preceding the target was determined randomly for each trial, varying between 11 and 15. The color of the non-targets was randomly determined for each trial under the constraint that the same color was never presented successively. When presented, distractor displays consisted of a 100-ms exposure of four rectangular frames, that were centered 5.5° above, below, to the right, and to the left of the central stream. The distractor display was presented 200 ms prior to the target, together with one of the central letters that preceded the target. Under the face-distractor condition, a peripheral facial image was embedded in one of the frames. Under the face-control condition, a Fourier-transformed image was embedded in the periphery in one of the frames. Under the frame condition, only the four rectangular frames were presented. Under the no-distractor condition, no peripheral distractor was presented. Observers identified the target using corresponding keys on the keyboard, and the accuracy rate was recorded. No speeded responses were required. These four conditions (80 trials each) were intermixed in an experimental block, which was preceded by 12 practice trials. Results The mean of accuracies of correct responses is shown in Fig. 2 as a function of conditions. A one-way ANOVA on the mean accuracies of correct responses revealed a significant main effect, F(3, 54) = 7.54, p = 0.0003, g2p = 0.30. The test for multiple comparisons revealed higher rates of correct responses under the no-distractor than under the frame, face, and face-control conditions, p \ 0.05, a = 0.013, 0.008, and 0.010, respectively. Comparisons involving other conditions, including the face and face-control conditions, were not significant, a = 0.05. Discussion The results of Experiment 1 reflect the occurrence of attentional capture. However, the capture was not specific
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letter was displayed for 67 ms followed by an inter-stimulus interval of 33 ms, yielding a presentation rate of 10 items per second. These temporal parameters of the central stream were maintained throughout Experiments 2 and 3.
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Fig. 2 Mean percentages of correct responses as a function of distractor conditions in Experiment 1. Error bars indicate standard errors
to faces: accuracy rates under conditions involving the appearance of any object (frame, face, and control-face conditions) were lower than those under the no-distractor condition, implying that the abrupt onset of any object captured attention (Christ & Abrams, 2006; Jonides & Yantis, 1988). The lower level of accuracy under all distractor conditions is inconsistent with the view that attentional capture depends on a current goal of searching for target colors only. According to this view, when observers engage in a letter identification task, any facial and control images that are irrelevant to the current behavioral goal should not capture attention. The impairment observed in the present experiment may have been due to participants’ involuntary attentional orientation to all distractors, because the distractors were temporally informative of the targets (i.e., they were presented with a fixed interval before the targets), although such an attentional shift would actually interfere with the selective search for target colors. In any event, we found no evidence of face-specific attentional capture. If facial images per se were especially able to capture attention, accuracy under the face condition should have been significantly lower than that under the control-face condition. Instead, the accuracy rates under the face condition were comparable to those under the conditions in which frames and control facial images appeared. It should be noted that the facial images were not followed by masking items and were clearly visible. Additionally, the images were large (8.9° 9 12.3°). In fact, some participants reported that they found a few stimulus
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images highly attractive. Therefore, the present results challenge the view that faces capture attention in a stimulus-driven way (Langton et al., 2008; Theeuwes & Van der Stigchel, 2006), at least under the present testing conditions. Nonetheless, we need to verify that the timing of the present procedure was sensitive enough to measure attentional capture by facial images because it has been demonstrated that natural images can be processed relatively quickly (e.g., Rousselet, Mace´, & Fabre-Thorpe, 2003). We examined this possibility in the next experiment, in which face distractors coincided with the target or with the item immediately preceding the target.
Experiment 2 Experiment 1 demonstrated no effect of face-specific attentional capture although visual onset interfered with target identification in all distractor condition. Given that the visual system can process natural images very efficiently and quickly (e.g., Li, VanRullen, Koch, & Perona, 2002; Rousselet et al., 2003; Kirchner & Thorpe, 2006), the present facial images may also have been processed with a minimal temporal delay, and this may have obscured the impact of capture in Experiment 1 because the temporal lag between the distractor and the target was too long. Experiment 2 examined whether attentional capture by faces could be detected when the temporal lag between the distractor and the target was shorter than that in the previous experiment. Specifically, the distractor frame coincided with the target or with the item immediately preceding the target (100 ms before the onset of the target). If the absence of attentional capture by faces were due to a rapid engagement/disengagement of attention, we would Fig. 3 Mean percentages of correct responses as a function of distractor conditions in Experiment 2. Error bars indicate standard errors
expect that the stimulus onset asynchrony (SOA) between the distractor frame and the target frame made a difference for the results—with more face-specific capture under the present short-SOA conditions than in Experiment 1. Method Twenty-six undergraduate and graduate students (8 males and 18 females, aged 18–23 years, M = 20.2) with normal or corrected-to-normal vision participated. The stimuli and procedure were identical to those in Experiment 1, except that the SOA between the distractor frame and the target frame differed. Stimuli were presented on an LCD computer monitor. The distractor was presented simultaneously with the target or with the item directly preceding the target (i.e., the distractor-target SOA of 0 or 100 ms, respectively) and disappeared after 100 ms of exposure. The four distractor types (no-distractor, frame, face-distractor, or face-control conditions) were presented in a manner orthogonal to the two distractor-target SOAs (0 or 100 ms), intermixed within an experimental block (320 trials in total), and preceded by 12 practice trials. We treated the SOA (0 or 100 ms) as a dummy variable when no distractor was presented. Although the values of 0 and 100 ms were internally assigned as the SOA parameter, they looked identical in appearance to the observers. Results The mean percentages of correct responses under each condition are presented in Fig. 3. A two-way ANOVA on the mean accuracies of correct responses was conducted with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: the no distractor, frame, controlface, and face-distractor conditions). The main effect of
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distractor condition was significant, F(3, 75) = 4.82, p = 0.004, g2p = 0.16. Multiple comparisons indicated that the accuracy was significantly lower under the face-distractor condition than under the no-distractor, frame, and face-control conditions, p \ 0.05, a = 0.0125, 0.0083, and 0.0100, respectively. Both the main effect of SOA and the interaction between SOA and distractor presentation were not significant, F(1, 25) = 0.79, p = 0.38, g2p = 0.03, and F(3, 75) = 0.78, p = 0.51, g2p = 0.03, respectively. Discussion The present experiment was performed because people can process natural images very quickly and efficiently (Thorpe, Fize, & Marlot, 1996; Kirchner & Thorpe, 2006; Rousselet et al., 2003). Thus, a face-specific attentional capture effect would have been undetectable in the context of the relatively long (i.e., 200 ms) target-distractor SOA in Experiment 1. In contrast in the present experiment that adopted much shorter SOAs revealed a face-specific attentional capture effect. The difference between the present conditions and the 200-ms target-distractor SOA was substantial: the faces interfered with target identification (i.e., attentional capture) in the present experiment, whereas no such facespecific capture was observed in Experiment 1. Given that faces are detected rapidly (e.g., within *100 ms; Rousselet et al., 2003), it is plausible that an efficient face-processing system would support quick engagement and disengagement of attention. Along these lines, our finding of the lowest accuracy under the face condition compared with the other conditions in Experiment 2 indicates that attentional focus was captured by the face distractor presented with or 100 ms before the target and that attention remained on this distractor for a measureable period of time (Bindemann, Burton, Hooge, Jenkins, & De Haan, 2005). Thus, respondents were unable to return their attention to the central stream when the target appeared. The mere presence of a frame was not associated with attentional capture in the present experiment. Although this pattern of results was observed in Experiments 2 and 3 (see below), the onset of a frame had an effect in Experiment 1, which may reflect stimulus-driven attentional capture by transient luminance changes (e.g., Franconeri et al., 2005). Because the effect of onset was unreliable and tangential to the main focus of this article (i.e., the effect of face distractors), we do not consider it further. The results of these experiments demonstrating that visual attention is captured by the presence of faces are inconsistent with the view that the deployment of attention depends on observers’ current behavioral goals. This principle was tested in the present experiment in that the face distractors were entirely task irrelevant in terms of the
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definition of targets and the spatial scope of the task. Specifically, the task of the observers was to identify a target letter, as defined by a designated color, embedded in a central rapid stream of heterogeneously colored nontargets. The targets never appeared in the periphery. Therefore, the faces presented outside the central stream were entirely irrelevant to observers’ task. If the deployment of attention had been governed by top-down control, such task-irrelevant peripheral distractors would have been ignored. The present results indicate that this was not the case.
Experiment 3 In the present experiment, we extended the findings of the previous experiment in which we demonstrated attentional capture by task-irrelevant face distractors, as the ability of faces in general to capture attention under the present experimental conditions remains unclear. Specifically, the face stimuli used in Experiments 1 and 2 were the 80 among *2,000 female faces that were rated as most attractive. Thus, the attentional capture observed in Experiments 2 and 3 may have been specific to the present stimulus set of extremely salient stimuli. Because pictures of attractive females are more likely than those of attractive males or females and males of average appearance to produce attentional capture according to research using a dot-probe task (Maner, Gaillio, & DeWall, 2007), exogenous attentional capture by faces may be limited to the specific stimulus set used in the first three experiments. Therefore, to expand upon the prior results, we replaced the distractor stimuli with a different set of facial images, including males, in Experiment 3. Method Twenty-one undergraduate and graduate students (5 males and 16 females, aged 18–22 years, M = 21.0 years) with normal or corrected-to-normal vision were recruited. With the exception of the distractor faces, the stimuli, apparatus, and procedure were identical to those in Experiment 2. Facial images for the distractor conditions were collected from Internet websites of Japanese local municipal council members (40 males and 40 females; color bitmap images of 354 9 472 pixels). Three raters, including the authors, rated these 80 images and those used in Experiments 1–3 using a 1–100 visual analog scale (1 unattractive and 100 very attractive). The mean ratings were 17.52 for the new set of 80 (a = 0.882) and 56.49 (a = 0.919) for the original set of images. These ratings indicate that the facial images in the new set were less attractive than those used in Experiments 1–3.
Psychological Research Fig. 4 Mean percentages of correct responses as a function of distractor conditions in Experiment 3. Error bars indicate standard errors
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Results and discussion The mean percentage of correct responses under each condition is presented in Fig. 4. A two-way ANOVA on the mean accuracies of correct responses was performed with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: no-distractor, frame, controlface, and face-distractor conditions). The main effects of SOA condition, F(1, 20) = 6.48, p = 0.0193, g2p = 0.25, and of the distractor type, F(3, 60) = 2.82, p = 0.0467, g2p = 0.12, were significant. The interaction between distractor type and SOA was also significant, F(3, 60) = 3.90, p = 0.0131, g2p = 0.16. A test for multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than that under the control-face distractor condition, p \ 0.05, a = 0.0083. No other comparisons showed significant differences, a [ 0.01. The results of Experiment 3 reflect attentional capture by faces. The accuracy with which targets were identified under the face condition was lower than that under the control condition even when less attractive pairs of stimulus images were used. These results suggest that faces overcome the observer’s attentional set and capture attention regardless of their attractiveness.
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Fourier-scrambled images served as controls with respect to low-level features by maintaining the same spatial frequencies and color spectra as the originals, confounds were introduced in that the original face images were structured, symmetrical, and meaningful, whereas the control images were not. Therefore, we replaced the upright face images with inverted versions of the same faces (the face inversion effect; Yin, 1969). If the inverted faces captured attention, the attentional capture observed in the present study could be attributed to the presence of any meaningfulness, structure, or symmetry in the image. In contrast, if attentional capture disappeared when these images were presented, we could attribute attentional capture solely to the presence of upright faces. Method Twenty-one undergraduate students (2 males and 19 females, aged 18–20 years, M = 19.0 years) with normal or corrected-to-normal vision were recruited for participation in this study. With the exception of the distractor faces, the stimuli, apparatus, and procedure were identical to those in Experiment 1. All the distractor-face and controlface images were inverted in the present experiment. Results and discussion
Experiment 4 The results thus far demonstrate that faces capture attention regardless of the observer’s attentional set and the attractiveness (Experiments 2 and 3). Nonetheless, it is possible that the attentional capture observed in the present study was caused not by the presence of the faces per se but by artifacts, such as the presence of structured, symmetrical, and/or meaningful objects. In other words, although the
The mean percentages of correct responses under each condition are presented in Fig. 5. A two-way ANOVA on the mean accuracies of correct responses was performed with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: no-distractor, frame, controlface, and face-distractor conditions). The main effects of the SOA, F(1, 20) = 4.54, p = 0.0458, g2p = 0.18, and of distractor type, F(3, 60) = 3.75, p = 0.0155, g2p = 0.16,
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Psychological Research Fig. 5 Mean percentages of correct responses as a function of distractor conditions in Experiment 4. Error bars indicate standard errors
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were significant. The interaction between distractor type and SOA was not significant, F(3, 60) = 1.23, p = 0.3065, g2p = 0.058. A test for multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than under the frame condition, p \ 0.05, a = 0.0083. Importantly, no other comparisons revealed significant differences, including between the face and control-face conditions, a [ 0.01. Although the present results revealed no attentional capture by inverted faces, this conclusion is based on a nonsignificant difference between the face and face-control condition. To bolster our claim that task-irrelevant (upright) faces capture attention, we conducted an additional ANOVA with one between-subject factor [face orientation: upright or inverted (i.e., Experiment 3 or 4)] and two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: frame, face, and face-control distractor conditions). The results indicated significant main effects of the SOA, F(1, 40) = 11.39, p = 0.002, g2p = 0.22, and of distractor type, F(2, 80) = 9.57, p \ 0.001, g2p = 0.19. Importantly, a significant interaction between face orientation and distractor type was found, F(2, 80) = 3.19, p = 0.0465, g2p = 0.074. Multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than under the face-control condition, p = 0.035, a \ 0.05, in Experiment 3. No such difference was found between the inverted face and its corresponding face-control condition in Experiment 4, p = 0.1225, a [ 0.05. These results support our claim that only upright face distractors captured attention. The results revealed that the accuracy with which the target was identified under the inverted-face condition did not differ from that under the control-face condition. These results suggest that the alternative explanation was not
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viable in that the mere presence of meaning, structure, and/ or symmetry in the inverted-face images did not produce attentional capture. Rather, the results of Experiment 4 support our argument that (upright) faces break through observers’ behavioral goal of searching for a letter of a specific color and capture attention. The present results also help to rule out another possibility that the present capture effect by faces hinges on a color similarity between the face images and the targets. Specifically, one could argue that there was more color overlap between the face images and the targets than between the other distractors and the targets. Because the color spectra of the present face images were identical to those in Experiment 2, attentional capture should have occurred if the color overlap governed the capture effect. In fact, this was not the case. The disappearance of the capture effect (i.e., difference between the critical two conditions, the face vs. face-control conditions) clearly indicates that the capture effect cannot be attributed to the color overlap between face images and targets.
General discussion The present study examined whether faces have a special ability to capture visual attention even when they are irrelevant to the observer’s current behavioral goal. Specifically, previous studies have emphasized that the human visual system is sensitive to faces and that the processing of such biologically important stimuli occurs automatically, resulting in attentional orienting toward task-irrelevant faces (Langton et. al., 2008; Bindemann et al., 2005; Theeuwes & Van der Stigchel, 2006). In other words, previous studies have interpreted findings that face
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distractors impair visual search performance as reflective of the special status of faces as critical stimuli that automatically attract attention. However, previous studies were actually inconclusive in this regard because they were not designed to examine whether attentional capture occurs even when faces are entirely irrelevant to the task and because they did not carefully control the role of attentional set when faces were used as targets or non-targets in visual search. The role of attentional set in visual searches involving faces was thus underestimated in most cases. The present study carefully controlled the observer’s attentional set in that the target in the task of identifying the central letter did not share features with the peripheral face distractors. In Experiment 1, the face-specific attentional capture effect was not observed. However, Experiments 2 and 3 showed that faces captured attention when they were completely task irrelevant. The only difference between Experiments 1 and 2 was that of the distractor-target SOA, which was shorter in Experiment 2 than in Experiment 1. The present capture effect was not limited to attractive faces because average-looking faces also captured attention in Experiment 3. Experiment 4 demonstrated that the attentional capture obtained in the present study was due to the presence of upright faces, rather than to that of symmetrical, structured, meaningful objects. These results suggest that attentional capture by faces occurs regardless of attentional set. Although the idea of exogenous attentional capture by faces is not new (Langton et al., 2008; Lavie et al., 2003) from the perspective that attentional capture occurs automatically (Theeuwes, 2010), the present study demonstrated that even entirely task-irrelevant faces are special in this regard. The present finding suggests that faces overcome attentional set regardless of their attractiveness. Importantly, the present study demonstrated attentional capture by faces defined by the differences in accuracies between the face and face-control conditions under short SOAs between the face and the target frames. This pattern of results contrasts sharply with the typical temporal profile of attentional capture by color singletons (e.g., Folk et al., 2002). For example, an SOA of *200 ms was necessary for a peripheral color singleton serving as a distractor to capture attention when observers viewed a central stream of letters to identify a uniquely colored target (Folk et al., 2002). That is, distractors need to be presented before the target to attract attention. In contrast with this relatively slow time course, the face distractors used in the present study exerted effects even when they were presented simultaneously with the target. The rapidity with which humans process natural images contributes to the rapidity of capture (Li, VanRullen, Koch, & Perona, 2002; Rousselet et al., 2003; Kirchner & Thorpe, 2006). It should be noted that the present study was not designed to examine whether spatial focus of attention was
exogenously drawn to the task-irrelevant peripheral faces. Several previous experiments (e.g., Folk et al., 2002, Experiment 3) were specifically designed to demonstrate that the spatial focus of attention shifted to peripheral distractors. However, in the present study, it was not clear whether attention was captured or whether faces increased some form of non-spatial filtering costs (cf. Folk & Remington, 1998). Although the present task was designed to eliminate overlap between the spatial definitions of the target and face distractors, this does not mean that the spatial component of attention was involved in the present attentional capture effect. It is conceivable that a spatial component may not be involved. Specifically, different group of researchers (e.g., Folk, Leber, & Egeth, 2008; Ghorashi, Zuvic, Visser, & Di Lollo, 2003; Inukai, Kawahara, & Kumada, 2010; Kahneman, Treisman, & Burkell, 1983) have found some types of attentional capture implying no involvement of spatial shift of attention in contrast to standard definition of attentional capture. Therefore, further studies are required to determine whether attentional capture is involved in the cost in reaction times incurred by irrelevant faces. The view that faces have a special ability related to attentional control is also consistent with previous studies (e.g., Langton et al., 2008; Lavie et al., 2003). Some of the procedures of those studies were similar to those of the present study, including the intersection between observer’s attentional set and the locations of facial stimuli. It should be noted that Lavie and colleagues demonstrated examples of ‘‘faces’’ capturing attention when they were clearly irrelevant. For example, Forster and Lavie (2008) found a delay in visual search when cartoon characters as irrelevant distractors suddenly appeared outside the search array. It was unclear whether this delay was face specific because the researchers compared the presence or absence of cartoon figures. Therefore, the mere presence of meaningful objects may have been sufficient to produce the effect. Another example (Jenkins, Lavie, & Driver, 2003) revealed that faces function differently from other types of distractors, suggesting face-specific capacity limitations. This does not necessarily mean that faces capture attention regardless of the observer’s task set. In fact, distractor images presented in the periphery were response congruent (therefore, beneficial for conducting the task) in half of the trials, and the face images shared the same peripheral locations in their study. Therefore, observers might have had an incentive to monitor those peripheral locations and distractors that fell in that location. The present study differed from these previous studies in that we examined conditions under which faces were totally irrelevant to the experimental task. The present study directly investigated whether faces capture attention regardless of endogenously established attentional set. The results demonstrate that
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faces are special in terms of attentional capture and can overcome the control of attentional set in that completely task-irrelevant faces, regardless of attractiveness, were able to break through a top-down attentional set given a brief distractor-target SOA. Acknowledgments This study was supported by Grant-in-Aid for Scientific Research on Innovative Areas, ‘‘Face perception and recognition’’ from MEXT KAKENHI 23119731 to JK. We thank Shoko Kanaya for her helpful comments on this work.
References Ansorge, U., & Heumann, M. (2003). Top-down contingencies in peripheral cuing: the role of color and location. Journal of Experimental Psychology: Human Perception and Performance, 29, 937–948. Bacon, W. F., & Egeth, H. E. (1994). Overriding stimulus-driven attentional capture. Perception and Psychophysics, 55, 485–496. Bindemann, M., Burton, A. M., Hooge, I. T. C., Jenkins, R., & DeHaan, E. H. F. (2005). Faces retain attention. Psychonomic Bulletin & Review, 12, 1048–1053. Bindemann, M., Burton, A. M., Langton, S. R. H., Schweinberger, S. R., & Doherty, M. J. (2007). The control of attention to faces. Journal of Vision, 7, 1–8. Brainard, D. H. (1997). The Psychophysics Toolbox. Spatial Vision, 10, 433–436. Cerf, M., Harel, J., Einha¨user, W., & Koch, C. (2008). Predicting human gaze using low-level saliency combined with face detection. Advances in Neural Information Processing (NIPS), 2007(20), 241–248. Chen, P., & Mordkoff, J. T. (2007). Contingent capture at a very short SOA: evidence against rapid disengagement. Visual Cognition, 15, 637–646. Christ, S. E., & Abrams, R. A. (2006). Abrupt onsets cannot be ignored. Psychonomic Bulletin & Review, 13, 875–880. Eastwood, J. D., Smilek, D., & Merikle, P. M. (2001). Differential attentional guidance by unattended faces expressing positive and negative emotion. Perception & Psychologics, 63, 1004–1013. Einha¨user, W., Rutishauser, U., & Koch, C. (2008). Task-demands can immediately reverse the effects of sensory-driven saliency in complex visual stimuli. Journal of Vision, 8, 1–19. Folk, C. L., Leber, A. B., & Egeth, H. E. (2002). Made you blink! Contingent attentional capture produces a spatial blink. Perception and Psychophysics, 64, 741–753. Folk, C. L., Leber, A. B., & Egeth, H. E. (2008). Top-down control settings and the attentional blink: evidence for non-spatial contingent capture. Visual Cognition, 16, 616–642. Folk, C. L., & Remington, R. (1998). Selectivity in distraction by irrelevant featural singletons: evidence for two forms of attentional capture. Journal of Experimental Psychology: Human Perception and Performance, 24, 847–858. Folk, C. L., Remington, R. W., & Johnston, J. C. (1992). Involuntary covert orienting is contingent on attentional control settings. Journal of Experimental Psychology: Human Perception and Performance, 18, 1030–1044. Forster, S., & Lavie, N. (2008). Failures to ignore entirely irrelevant distractors: the role of load. Journal of Experimental Psychology: Applied, 14, 73–83. Franconeri, S. L., Hollingworth, A., & Simons, D. J. (2005). Do new objects capture attention? Psychological Science, 16, 275–281. Ghorashi, S. M. S., Zuvic, S. M., Visser, T. A. W., & Di Lollo, V. (2003). Focal distraction: spatial shifts of attentional focus are
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not required for contingent capture. Journal of Experimental Psychology: Human Perception and Performance, 29, 78–91. ´ ., & Johnson, M. H. (2004). FaceHalit, H., Csibra, G., Volein, A sensitive cortical processing in early infancy. Journal of Child Psychology and Psychiatry, 45, 1228–1234. Inukai, T., Kawahara, J.-I., & Kumada, T. (2010). Nonspatial interdimensional attentional capture. Attention, Perception, & Psychophysics, 72, 658–666. Jenkins, R., Lavie, N., & Driver, J. (2003). Ignoring famous faces: category specific dilution of distractor interference. Perception and Psychophysics, 65, 298–309. Jonides, J., & Yantis, S. (1988). Uniqueness of abrupt visual onset in capturing attention. Perception and Psychophysics, 43, 346–354. Kahneman, D., Treisman, A., & Burkell, J. (1983). The cost of visual filtering. Journal of Experimental Psychology: Human Perception and Performance, 9, 510–522. Kawahara, J., Yanase, K., & Kitazaki, M. (2012). Attentional capture by the onset and offset of motion signals outside the spatial focus of attention. Journal of Vision, 12, 1–13. Kirchner, H., & Thorpe, S. (2006). Ultra-rapid object detection with saccadic eye movements: visual processing speed revisited. Vision Research, 46, 1762–1776. Langton, S. R. H., Law, A. S., Burton, A. M., & Schweinberger, S. R. (2008). Attention capture by faces. Cognition, 107, 330–342. Lavie, N., Ro, T., & Russell, C. (2003). The role of perceptual load in processing distractor faces. Psychological Science, 14, 510–515. Leber, A. B., & Egeth, H. E. (2006). It’s under control: top-down search strategies can override attentional capture. Psychonomic Bulletin & Review, 13, 132–138. Lien, M.-C., Ruthruff, E., Goodin, Z., & Remington, R. W. (2008). Contingent attentional capture by top-down control settings: converging evidence from event-related potentials. Journal of Experimental Psychology: Human Perception and Performance, 34, 509–530. Li, F. F., VanRullen, R., Koch, C., & Perona, P. (2002). Rapid natural scene categorization in the near absence of attention. Proceeding of the National Academy of Sciences, 99, 9596–9601. Maner, J. K., Gailliot, M. T., & DeWall, C. N. (2007). Adaptive attentional attunement: evidence for mating-related perceptual bias. Evolution and Human Behavior, 28, 28–36. Pelli, D. G. (1997). The VideoToolbox software for visual psychophysics: transforming numbers into movies. Spatial Vision, 10, 437–442. Pratt, J., & McAuliffe, J. (2002). Determining whether attentional control settings are inclusive or exclusive. Perception and Psychophysics, 64, 1361–1370. Ro, T., Russell, C., & Lavie, N. (2001). Changing faces: a detection advantage in the flicker paradigm. Psychological Science, 12, 94–99. Rousselet, G. A., Mace´, M. J.-M., & Fabre-Thorpe, M. (2003). Is it an animal? Is it a human face? Face processing in upright and inverted natural scenes. Journal of Vision, 3, 440–455. Schreij, D., Owens, C., & Theeuwes, J. (2008). Abrupt onsets capture attention independent of top-down control settings. Perception and Psychophysics, 70, 208–218. Shapiro, K. L., Arnell, K. M., & Raymond, J. E. (1997). The attentional blink. Trends in Cognitive Science, 1, 291–296. Theeuwes, J. (2010). Top-down and bottom-up control of visual selection. Acta Psychologica, 135, 77–99. Theeuwes, J., & Van der Stigchel, S. (2006). Faces capture attention: evidence from inhibition of return. Visual Cognition, 13, 657–665. Thorpe, S., Fize, D., & Marlot, C. (1996). Speed of processing in the human visual system. Nature, 381, 520–522. Van der Stigchel, S., Belopolsky, A. V., Peters, J. C., Wijnen, J. G., Meeter, M., & Theeuwes, J. (2009). The limits of top-down control of visual attention. Acta Psychologica, 132, 201–212.
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Experimental Psychology: Human Perception and Performance, 39, 861–871. Yin, R. K. (1969). Looking at upside-down faces. Journal of Experimental Psychology, 81, 141–145.
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ORIGINAL ARTICLE
Attentional capture by completely task-irrelevant faces Shiori Sato • Jun I. Kawahara
Received: 14 January 2014 / Accepted: 9 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract The present study investigated whether faces capture attention regardless of attentional set. The presentation of a face as a distractor during a visual search has been shown to impair performance relative to when the face was absent, implying that faces automatically attract attention. If attentional control is contingent on the observer’s current goal, faces should not capture attention when they are irrelevant to the observer’s attentional set. Previous studies demonstrating face-induced attentional capture used faces that were relevant to the task. Thus, a task in which faces were completely irrelevant to the observer’s set was created. Participants identified a target letter among heterogeneously colored non-targets while ignoring a peripheral facial image that appeared as a brief distractor. No face-specific capture was observed when the targetdistractor stimulus onset asynchrony (SOA) was long (Experiment 1). When the SOA was shortened, attentional capture by irrelevant faces was observed (Experiment 2). Experiment 3 extended this finding to all conditions, regardless of the attractiveness of faces. No such capture effect was found in Experiment 4 with inverted-face distractors. These results indicate that completely task-irrelevant faces break through top-down attentional set given a brief distractor-target SOA.
S. Sato J. I. Kawahara (&) Department of Psychology, Chukyo University, 101-2 Yagoto, Showa, Nagoya 466-8666, Japan e-mail: [email protected] J. I. Kawahara National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
Introduction Of the various objects and events in our visual environment, it is reasonable to assume that our attention shifts to extremely salient stimuli (e.g., an approaching fire engine while driving). This assumption is supported by considerable evidence that salient stimuli are quickly and accurately perceived, demonstrating that visual attention is oriented to the abrupt onset of salient objects or events regardless of observers’ current behavioral goals (Franconeri, Hollingworth, & Simons, 2005; von Mu¨hlenen & Lleras, 2007; Schreij, Owens, & Theeuwes, 2008). Similarly, the presence of such salient stimuli (Kawahara, Yanase, & Kitazaki, 2012; Van der Stigchel et al., 2009) impairs performance when they act as distractors. It is also widely accepted that visual attention is oriented toward objects of great biological and social significance. For example, human faces expressing a negative emotion are detected more efficiently than faces expressing a neutral emotion (Eastwood, Smilek, & Merikle, 2001). Furthermore, the mere presence of a distractor face, regardless of expression, has been shown to delay visual search relative to cases in which no distractor face was presented, implying that faces summon attention when they are presented within (Langton, Law, Burton, & Schweinberger, 2008) or outside of (Lavie, Ro, & Russell, 2003) a visual search display. A computational model better predicted voluntary eye gaze purportedly preceded by attentional shift when face detection was incorporated than when no such components were included (Cerf, Harel, Einha¨user, & Koch, 2008). Moreover, Theeuwes & Van der Stigchel (2006) have provided strong evidence for stimulus-driven orienting toward task-irrelevant faces by demonstrating inhibition of return (delayed responding with a saccade) to a location that previously contained a face.
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These results suggest that faces are processed automatically. However, it is unclear whether these results mean that faces capture attention regardless of observers’ current behavioral goals. Given recent findings that attentional capture can be exogenous, it is important to determine whether stimulus-driven orienting of attention can be modulated by endogenous, top-down control (Einha¨user, Rutisha¨user, & Koch, 2008; Wyble, Folk, & Potter, 2013). However, the aforementioned studies implying automatic and necessary attentional capture by faces are inconsistent with evidence for intentional flexible attentional control. Specifically, researchers have shown that attentional capture by irrelevant distractors can be eliminated when a task is designed to prompt observers to adopt an attentional set that involves searching for a particular color (Ansorge & Heumann, 2003; Chen & Mordkoff, 2007; Folk & Remington, 1998; Folk, Remington, & Johnston, 1992; Lien, Ruthruff, Goodin, & Remington, 2008; Pratt & McAuliffe, 2002). This type of attentional control is sufficiently powerful to override stimulus-driven capture (Bacon & Egeth, 1994; Leber & Egeth, 2006). The purpose of the present study was to reconcile this apparent inconsistency regarding the attentional capture elicited by face distractors. If the visual system were, in general, capable of configuring top-down attentional control for visual searches involving not only simple features such as colors and shapes, but also more complex visual patterns, attentional capture by faces should be eliminated owing to flexible attentional control settings. However, attentional capture has been shown to be elicited by task-irrelevant faces (e.g., Langton et al., 2008). Nonetheless, we argue that it seems premature to conclude that faces are endowed with a special ability to capture attention. Indeed, careful examination of previous studies supporting automatic attentional capture by faces revealed that such studies were not designed to examine whether entirely task-irrelevant faces can capture attention. For example, studies in which observers’ primary goal was to search for faces do not tell us whether the visual system can exclude task-irrelevant face distractors (Eastwood et al., 2001) because, by definition, faces were targets (i.e., task relevant) in those circumstances. Thus, it is reasonable to assume that a face singleton would be processed and would affect visual performance. The same concern applies to studies that have supposedly demonstrated automatic attentional capture by faces by showing that the reaction times for visual searches were longer when a face distractor was included in a search array than when no such item was included (e.g., Langton et al., 2008; Ro, Russell, & Lavie, 2001). Face distractors shared similar features (size and color) with the search targets themselves. Moreover, most face distractors in those studies were presented at potential target locations
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(e.g., Theeuwes & Van der Stigchel, 2006; Langton et al., 2008; Bindemann, Burton, Langton, Schweinberger, & Doherty, 2007). Therefore, faces were a part of observers’ attentional set in these previous studies, and it remains unclear whether faces can break through such an attentional set when they are entirely task irrelevant. The present study examined this question. To introduce faces as entirely task-irrelevant distractors, the features that differentiate targets from non-target filler items should not overlap with those that define the distractor. To fulfill this requirement, we adopted an established paradigm that has been used to measure attentional capture by task-irrelevant distractors (Folk, Leber, & Egeth, 2002). This task is similar to those used in attentional blink studies (Shapiro et al., 1997) and rests on the widespread assumption that limited attentional resources are associated with deficits in cognitive processing. Specifically, in the original study conducted by Folk et al. (2002), observers searched for a target letter, as defined by a color (i.e., green), embedded in a rapid central stream of non-target heterogeneously colored letters. A task-irrelevant distractor (e.g., a pound sign) was briefly presented outside the current spatial focus of attention (above, below, to the left, or to the right of the central letter stream) before the target appeared. The researchers found no differences between irrelevant distractors and no distractors and sometimes these authors observed slightly impaired target identification with irrelevant color distractors as compared to no distractors. However, identification accuracy decreased when a distractor shared a feature with the target (green), implying that attentional capture is contingent on observers’ goals. This deficit has been attributed to the temporary unavailability of attentional resources that are diverted to the distractor. In the present study, the facial image that served as the distractor was displayed outside the central letter stream. Thus, we ensured that the faces were completely task irrelevant. We reasoned that if the visual processing of faces were automatic and if the faces capture attention regardless of observers’ behavioral goals, identification of a target letter should be more impaired when a distractor face was presented at an entirely task-irrelevant peripheral location relative to when no such distractor was presented or to when a control (scrambled) facial image was presented.
Experiment 1 The present experiment compared the accuracy of targetletter identification under a condition in which a distractor face was presented briefly before the onset of the target (face condition) and under the following three control conditions: the face-control condition, in which a
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scrambled facial image was presented; the frame condition, in which a rectangular frame was presented; and the nodistractor condition. We predicted that if the abrupt onset of visual items captures attention, accurate target identification would be more impaired under the three distractor conditions than under the no-distractor condition. More importantly, if the onset of a face captures attention, observers would be less accurate under the face condition than under the face-control condition. Such a pattern of results would mean that faces have a special ability to capture attention. In contrast, if attentional capture were governed by observers’ set, no differences in the rates of accurate identification would be observed under the face and the face-control conditions. Method Participants Nineteen undergraduates and graduate students (7 males and 12 females, aged 18 and 22 years, M = 20.0 years recruited from the Chukyo University subject pool for this and the following experiments) with normal or corrected-to-normal vision were recruited and paid for their participation. Stimuli and apparatus The stimuli consisted of a rapid central stream of 20 heterogeneously colored (red, green, yellow, purple, or light
blue) uppercase letters (Fig. 1). The letters subtended a visual angle of *1° in height at a viewing distance of *45 cm and were displayed on a black background. Stimuli were generated by MATLAB 2010 with the Psychophysics Toolbox (Brainard, 1997; Pelli, 1997) and displayed at the center of a CRT computer screen (1,024 9 768 pixels driven at a 60-Hz refresh rate). The distractor faces were digitized from university yearbooks and saved as color bitmap images. Of the 1,932 female images originally scanned, we identified the 80 most attractive pictures based on ratings obtained from 31 raters who were not involved in the present study. In Experiment 1, we used enlarged versions of the same set of images (472 9 354 pixels, subtending 8.9° in height and 12.3° in width). The images used under the face-control condition were Fourier-scrambled versions of the same facial images (Halit, Csibra, Volein, & Johnson, 2004). These control images were created by randomizing the phase spectra of the faces while keeping the amplitude and color spectra constant. Specifically a two-dimensional fast Fourier transform was applied to the RGB color components of the original images. The phase on each frequency was replaced by a random value between -p and p (uniform distribution). The image was then reconverted by an inverse Fourier transform. The colors of the letters were chosen so that participants would adopt the feature-search mode: the target was red for odd-numbered participants, and the nontarget was green, yellow, purple, or light blue. Red was replaced with green for even-numbered participants. Each
Fig. 1 A schematic diagram of the stimulus sequence in Experiment 1. Participants were required to identify a red letter (target) embedded in a rapid sequence of non-target letters in homogenous colors (green, yellow, purple, and light blue). The SOA of the central sequence was 100 ms and a distractor frame (if any) appeared 200 ms before the target. A facial image could appear in one of the distractor frame (the image presented here with permission of Shiori Sato) (color figure online)
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Procedure and design
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At the beginning of each trial, a fixation cross was displayed at the center of the screen. Observers initiated each trial by pressing the spacebar. After a delay of 500 ms, a rapid stream of letters was presented. The stream consisted of 20 different non-target letters and a target (a green letter for half of the randomly assigned observers and a red one for the other half). The number of non-targets preceding the target was determined randomly for each trial, varying between 11 and 15. The color of the non-targets was randomly determined for each trial under the constraint that the same color was never presented successively. When presented, distractor displays consisted of a 100-ms exposure of four rectangular frames, that were centered 5.5° above, below, to the right, and to the left of the central stream. The distractor display was presented 200 ms prior to the target, together with one of the central letters that preceded the target. Under the face-distractor condition, a peripheral facial image was embedded in one of the frames. Under the face-control condition, a Fourier-transformed image was embedded in the periphery in one of the frames. Under the frame condition, only the four rectangular frames were presented. Under the no-distractor condition, no peripheral distractor was presented. Observers identified the target using corresponding keys on the keyboard, and the accuracy rate was recorded. No speeded responses were required. These four conditions (80 trials each) were intermixed in an experimental block, which was preceded by 12 practice trials. Results The mean of accuracies of correct responses is shown in Fig. 2 as a function of conditions. A one-way ANOVA on the mean accuracies of correct responses revealed a significant main effect, F(3, 54) = 7.54, p = 0.0003, g2p = 0.30. The test for multiple comparisons revealed higher rates of correct responses under the no-distractor than under the frame, face, and face-control conditions, p \ 0.05, a = 0.013, 0.008, and 0.010, respectively. Comparisons involving other conditions, including the face and face-control conditions, were not significant, a = 0.05. Discussion The results of Experiment 1 reflect the occurrence of attentional capture. However, the capture was not specific
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letter was displayed for 67 ms followed by an inter-stimulus interval of 33 ms, yielding a presentation rate of 10 items per second. These temporal parameters of the central stream were maintained throughout Experiments 2 and 3.
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Fig. 2 Mean percentages of correct responses as a function of distractor conditions in Experiment 1. Error bars indicate standard errors
to faces: accuracy rates under conditions involving the appearance of any object (frame, face, and control-face conditions) were lower than those under the no-distractor condition, implying that the abrupt onset of any object captured attention (Christ & Abrams, 2006; Jonides & Yantis, 1988). The lower level of accuracy under all distractor conditions is inconsistent with the view that attentional capture depends on a current goal of searching for target colors only. According to this view, when observers engage in a letter identification task, any facial and control images that are irrelevant to the current behavioral goal should not capture attention. The impairment observed in the present experiment may have been due to participants’ involuntary attentional orientation to all distractors, because the distractors were temporally informative of the targets (i.e., they were presented with a fixed interval before the targets), although such an attentional shift would actually interfere with the selective search for target colors. In any event, we found no evidence of face-specific attentional capture. If facial images per se were especially able to capture attention, accuracy under the face condition should have been significantly lower than that under the control-face condition. Instead, the accuracy rates under the face condition were comparable to those under the conditions in which frames and control facial images appeared. It should be noted that the facial images were not followed by masking items and were clearly visible. Additionally, the images were large (8.9° 9 12.3°). In fact, some participants reported that they found a few stimulus
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images highly attractive. Therefore, the present results challenge the view that faces capture attention in a stimulus-driven way (Langton et al., 2008; Theeuwes & Van der Stigchel, 2006), at least under the present testing conditions. Nonetheless, we need to verify that the timing of the present procedure was sensitive enough to measure attentional capture by facial images because it has been demonstrated that natural images can be processed relatively quickly (e.g., Rousselet, Mace´, & Fabre-Thorpe, 2003). We examined this possibility in the next experiment, in which face distractors coincided with the target or with the item immediately preceding the target.
Experiment 2 Experiment 1 demonstrated no effect of face-specific attentional capture although visual onset interfered with target identification in all distractor condition. Given that the visual system can process natural images very efficiently and quickly (e.g., Li, VanRullen, Koch, & Perona, 2002; Rousselet et al., 2003; Kirchner & Thorpe, 2006), the present facial images may also have been processed with a minimal temporal delay, and this may have obscured the impact of capture in Experiment 1 because the temporal lag between the distractor and the target was too long. Experiment 2 examined whether attentional capture by faces could be detected when the temporal lag between the distractor and the target was shorter than that in the previous experiment. Specifically, the distractor frame coincided with the target or with the item immediately preceding the target (100 ms before the onset of the target). If the absence of attentional capture by faces were due to a rapid engagement/disengagement of attention, we would Fig. 3 Mean percentages of correct responses as a function of distractor conditions in Experiment 2. Error bars indicate standard errors
expect that the stimulus onset asynchrony (SOA) between the distractor frame and the target frame made a difference for the results—with more face-specific capture under the present short-SOA conditions than in Experiment 1. Method Twenty-six undergraduate and graduate students (8 males and 18 females, aged 18–23 years, M = 20.2) with normal or corrected-to-normal vision participated. The stimuli and procedure were identical to those in Experiment 1, except that the SOA between the distractor frame and the target frame differed. Stimuli were presented on an LCD computer monitor. The distractor was presented simultaneously with the target or with the item directly preceding the target (i.e., the distractor-target SOA of 0 or 100 ms, respectively) and disappeared after 100 ms of exposure. The four distractor types (no-distractor, frame, face-distractor, or face-control conditions) were presented in a manner orthogonal to the two distractor-target SOAs (0 or 100 ms), intermixed within an experimental block (320 trials in total), and preceded by 12 practice trials. We treated the SOA (0 or 100 ms) as a dummy variable when no distractor was presented. Although the values of 0 and 100 ms were internally assigned as the SOA parameter, they looked identical in appearance to the observers. Results The mean percentages of correct responses under each condition are presented in Fig. 3. A two-way ANOVA on the mean accuracies of correct responses was conducted with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: the no distractor, frame, controlface, and face-distractor conditions). The main effect of
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distractor condition was significant, F(3, 75) = 4.82, p = 0.004, g2p = 0.16. Multiple comparisons indicated that the accuracy was significantly lower under the face-distractor condition than under the no-distractor, frame, and face-control conditions, p \ 0.05, a = 0.0125, 0.0083, and 0.0100, respectively. Both the main effect of SOA and the interaction between SOA and distractor presentation were not significant, F(1, 25) = 0.79, p = 0.38, g2p = 0.03, and F(3, 75) = 0.78, p = 0.51, g2p = 0.03, respectively. Discussion The present experiment was performed because people can process natural images very quickly and efficiently (Thorpe, Fize, & Marlot, 1996; Kirchner & Thorpe, 2006; Rousselet et al., 2003). Thus, a face-specific attentional capture effect would have been undetectable in the context of the relatively long (i.e., 200 ms) target-distractor SOA in Experiment 1. In contrast in the present experiment that adopted much shorter SOAs revealed a face-specific attentional capture effect. The difference between the present conditions and the 200-ms target-distractor SOA was substantial: the faces interfered with target identification (i.e., attentional capture) in the present experiment, whereas no such facespecific capture was observed in Experiment 1. Given that faces are detected rapidly (e.g., within *100 ms; Rousselet et al., 2003), it is plausible that an efficient face-processing system would support quick engagement and disengagement of attention. Along these lines, our finding of the lowest accuracy under the face condition compared with the other conditions in Experiment 2 indicates that attentional focus was captured by the face distractor presented with or 100 ms before the target and that attention remained on this distractor for a measureable period of time (Bindemann, Burton, Hooge, Jenkins, & De Haan, 2005). Thus, respondents were unable to return their attention to the central stream when the target appeared. The mere presence of a frame was not associated with attentional capture in the present experiment. Although this pattern of results was observed in Experiments 2 and 3 (see below), the onset of a frame had an effect in Experiment 1, which may reflect stimulus-driven attentional capture by transient luminance changes (e.g., Franconeri et al., 2005). Because the effect of onset was unreliable and tangential to the main focus of this article (i.e., the effect of face distractors), we do not consider it further. The results of these experiments demonstrating that visual attention is captured by the presence of faces are inconsistent with the view that the deployment of attention depends on observers’ current behavioral goals. This principle was tested in the present experiment in that the face distractors were entirely task irrelevant in terms of the
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definition of targets and the spatial scope of the task. Specifically, the task of the observers was to identify a target letter, as defined by a designated color, embedded in a central rapid stream of heterogeneously colored nontargets. The targets never appeared in the periphery. Therefore, the faces presented outside the central stream were entirely irrelevant to observers’ task. If the deployment of attention had been governed by top-down control, such task-irrelevant peripheral distractors would have been ignored. The present results indicate that this was not the case.
Experiment 3 In the present experiment, we extended the findings of the previous experiment in which we demonstrated attentional capture by task-irrelevant face distractors, as the ability of faces in general to capture attention under the present experimental conditions remains unclear. Specifically, the face stimuli used in Experiments 1 and 2 were the 80 among *2,000 female faces that were rated as most attractive. Thus, the attentional capture observed in Experiments 2 and 3 may have been specific to the present stimulus set of extremely salient stimuli. Because pictures of attractive females are more likely than those of attractive males or females and males of average appearance to produce attentional capture according to research using a dot-probe task (Maner, Gaillio, & DeWall, 2007), exogenous attentional capture by faces may be limited to the specific stimulus set used in the first three experiments. Therefore, to expand upon the prior results, we replaced the distractor stimuli with a different set of facial images, including males, in Experiment 3. Method Twenty-one undergraduate and graduate students (5 males and 16 females, aged 18–22 years, M = 21.0 years) with normal or corrected-to-normal vision were recruited. With the exception of the distractor faces, the stimuli, apparatus, and procedure were identical to those in Experiment 2. Facial images for the distractor conditions were collected from Internet websites of Japanese local municipal council members (40 males and 40 females; color bitmap images of 354 9 472 pixels). Three raters, including the authors, rated these 80 images and those used in Experiments 1–3 using a 1–100 visual analog scale (1 unattractive and 100 very attractive). The mean ratings were 17.52 for the new set of 80 (a = 0.882) and 56.49 (a = 0.919) for the original set of images. These ratings indicate that the facial images in the new set were less attractive than those used in Experiments 1–3.
Psychological Research Fig. 4 Mean percentages of correct responses as a function of distractor conditions in Experiment 3. Error bars indicate standard errors
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SOA = 100 ms
Accuracy (%)
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Results and discussion The mean percentage of correct responses under each condition is presented in Fig. 4. A two-way ANOVA on the mean accuracies of correct responses was performed with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: no-distractor, frame, controlface, and face-distractor conditions). The main effects of SOA condition, F(1, 20) = 6.48, p = 0.0193, g2p = 0.25, and of the distractor type, F(3, 60) = 2.82, p = 0.0467, g2p = 0.12, were significant. The interaction between distractor type and SOA was also significant, F(3, 60) = 3.90, p = 0.0131, g2p = 0.16. A test for multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than that under the control-face distractor condition, p \ 0.05, a = 0.0083. No other comparisons showed significant differences, a [ 0.01. The results of Experiment 3 reflect attentional capture by faces. The accuracy with which targets were identified under the face condition was lower than that under the control condition even when less attractive pairs of stimulus images were used. These results suggest that faces overcome the observer’s attentional set and capture attention regardless of their attractiveness.
Face
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Face
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Fourier-scrambled images served as controls with respect to low-level features by maintaining the same spatial frequencies and color spectra as the originals, confounds were introduced in that the original face images were structured, symmetrical, and meaningful, whereas the control images were not. Therefore, we replaced the upright face images with inverted versions of the same faces (the face inversion effect; Yin, 1969). If the inverted faces captured attention, the attentional capture observed in the present study could be attributed to the presence of any meaningfulness, structure, or symmetry in the image. In contrast, if attentional capture disappeared when these images were presented, we could attribute attentional capture solely to the presence of upright faces. Method Twenty-one undergraduate students (2 males and 19 females, aged 18–20 years, M = 19.0 years) with normal or corrected-to-normal vision were recruited for participation in this study. With the exception of the distractor faces, the stimuli, apparatus, and procedure were identical to those in Experiment 1. All the distractor-face and controlface images were inverted in the present experiment. Results and discussion
Experiment 4 The results thus far demonstrate that faces capture attention regardless of the observer’s attentional set and the attractiveness (Experiments 2 and 3). Nonetheless, it is possible that the attentional capture observed in the present study was caused not by the presence of the faces per se but by artifacts, such as the presence of structured, symmetrical, and/or meaningful objects. In other words, although the
The mean percentages of correct responses under each condition are presented in Fig. 5. A two-way ANOVA on the mean accuracies of correct responses was performed with two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: no-distractor, frame, controlface, and face-distractor conditions). The main effects of the SOA, F(1, 20) = 4.54, p = 0.0458, g2p = 0.18, and of distractor type, F(3, 60) = 3.75, p = 0.0155, g2p = 0.16,
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Psychological Research Fig. 5 Mean percentages of correct responses as a function of distractor conditions in Experiment 4. Error bars indicate standard errors
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SOA = 100 ms
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were significant. The interaction between distractor type and SOA was not significant, F(3, 60) = 1.23, p = 0.3065, g2p = 0.058. A test for multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than under the frame condition, p \ 0.05, a = 0.0083. Importantly, no other comparisons revealed significant differences, including between the face and control-face conditions, a [ 0.01. Although the present results revealed no attentional capture by inverted faces, this conclusion is based on a nonsignificant difference between the face and face-control condition. To bolster our claim that task-irrelevant (upright) faces capture attention, we conducted an additional ANOVA with one between-subject factor [face orientation: upright or inverted (i.e., Experiment 3 or 4)] and two within-subject factors (distractor-target SOA: 0 or 100 ms 9 distractor type: frame, face, and face-control distractor conditions). The results indicated significant main effects of the SOA, F(1, 40) = 11.39, p = 0.002, g2p = 0.22, and of distractor type, F(2, 80) = 9.57, p \ 0.001, g2p = 0.19. Importantly, a significant interaction between face orientation and distractor type was found, F(2, 80) = 3.19, p = 0.0465, g2p = 0.074. Multiple comparisons indicated that accuracy under the face-distractor condition was significantly lower than under the face-control condition, p = 0.035, a \ 0.05, in Experiment 3. No such difference was found between the inverted face and its corresponding face-control condition in Experiment 4, p = 0.1225, a [ 0.05. These results support our claim that only upright face distractors captured attention. The results revealed that the accuracy with which the target was identified under the inverted-face condition did not differ from that under the control-face condition. These results suggest that the alternative explanation was not
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Face
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No Frame Distractor
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viable in that the mere presence of meaning, structure, and/ or symmetry in the inverted-face images did not produce attentional capture. Rather, the results of Experiment 4 support our argument that (upright) faces break through observers’ behavioral goal of searching for a letter of a specific color and capture attention. The present results also help to rule out another possibility that the present capture effect by faces hinges on a color similarity between the face images and the targets. Specifically, one could argue that there was more color overlap between the face images and the targets than between the other distractors and the targets. Because the color spectra of the present face images were identical to those in Experiment 2, attentional capture should have occurred if the color overlap governed the capture effect. In fact, this was not the case. The disappearance of the capture effect (i.e., difference between the critical two conditions, the face vs. face-control conditions) clearly indicates that the capture effect cannot be attributed to the color overlap between face images and targets.
General discussion The present study examined whether faces have a special ability to capture visual attention even when they are irrelevant to the observer’s current behavioral goal. Specifically, previous studies have emphasized that the human visual system is sensitive to faces and that the processing of such biologically important stimuli occurs automatically, resulting in attentional orienting toward task-irrelevant faces (Langton et. al., 2008; Bindemann et al., 2005; Theeuwes & Van der Stigchel, 2006). In other words, previous studies have interpreted findings that face
Psychological Research
distractors impair visual search performance as reflective of the special status of faces as critical stimuli that automatically attract attention. However, previous studies were actually inconclusive in this regard because they were not designed to examine whether attentional capture occurs even when faces are entirely irrelevant to the task and because they did not carefully control the role of attentional set when faces were used as targets or non-targets in visual search. The role of attentional set in visual searches involving faces was thus underestimated in most cases. The present study carefully controlled the observer’s attentional set in that the target in the task of identifying the central letter did not share features with the peripheral face distractors. In Experiment 1, the face-specific attentional capture effect was not observed. However, Experiments 2 and 3 showed that faces captured attention when they were completely task irrelevant. The only difference between Experiments 1 and 2 was that of the distractor-target SOA, which was shorter in Experiment 2 than in Experiment 1. The present capture effect was not limited to attractive faces because average-looking faces also captured attention in Experiment 3. Experiment 4 demonstrated that the attentional capture obtained in the present study was due to the presence of upright faces, rather than to that of symmetrical, structured, meaningful objects. These results suggest that attentional capture by faces occurs regardless of attentional set. Although the idea of exogenous attentional capture by faces is not new (Langton et al., 2008; Lavie et al., 2003) from the perspective that attentional capture occurs automatically (Theeuwes, 2010), the present study demonstrated that even entirely task-irrelevant faces are special in this regard. The present finding suggests that faces overcome attentional set regardless of their attractiveness. Importantly, the present study demonstrated attentional capture by faces defined by the differences in accuracies between the face and face-control conditions under short SOAs between the face and the target frames. This pattern of results contrasts sharply with the typical temporal profile of attentional capture by color singletons (e.g., Folk et al., 2002). For example, an SOA of *200 ms was necessary for a peripheral color singleton serving as a distractor to capture attention when observers viewed a central stream of letters to identify a uniquely colored target (Folk et al., 2002). That is, distractors need to be presented before the target to attract attention. In contrast with this relatively slow time course, the face distractors used in the present study exerted effects even when they were presented simultaneously with the target. The rapidity with which humans process natural images contributes to the rapidity of capture (Li, VanRullen, Koch, & Perona, 2002; Rousselet et al., 2003; Kirchner & Thorpe, 2006). It should be noted that the present study was not designed to examine whether spatial focus of attention was
exogenously drawn to the task-irrelevant peripheral faces. Several previous experiments (e.g., Folk et al., 2002, Experiment 3) were specifically designed to demonstrate that the spatial focus of attention shifted to peripheral distractors. However, in the present study, it was not clear whether attention was captured or whether faces increased some form of non-spatial filtering costs (cf. Folk & Remington, 1998). Although the present task was designed to eliminate overlap between the spatial definitions of the target and face distractors, this does not mean that the spatial component of attention was involved in the present attentional capture effect. It is conceivable that a spatial component may not be involved. Specifically, different group of researchers (e.g., Folk, Leber, & Egeth, 2008; Ghorashi, Zuvic, Visser, & Di Lollo, 2003; Inukai, Kawahara, & Kumada, 2010; Kahneman, Treisman, & Burkell, 1983) have found some types of attentional capture implying no involvement of spatial shift of attention in contrast to standard definition of attentional capture. Therefore, further studies are required to determine whether attentional capture is involved in the cost in reaction times incurred by irrelevant faces. The view that faces have a special ability related to attentional control is also consistent with previous studies (e.g., Langton et al., 2008; Lavie et al., 2003). Some of the procedures of those studies were similar to those of the present study, including the intersection between observer’s attentional set and the locations of facial stimuli. It should be noted that Lavie and colleagues demonstrated examples of ‘‘faces’’ capturing attention when they were clearly irrelevant. For example, Forster and Lavie (2008) found a delay in visual search when cartoon characters as irrelevant distractors suddenly appeared outside the search array. It was unclear whether this delay was face specific because the researchers compared the presence or absence of cartoon figures. Therefore, the mere presence of meaningful objects may have been sufficient to produce the effect. Another example (Jenkins, Lavie, & Driver, 2003) revealed that faces function differently from other types of distractors, suggesting face-specific capacity limitations. This does not necessarily mean that faces capture attention regardless of the observer’s task set. In fact, distractor images presented in the periphery were response congruent (therefore, beneficial for conducting the task) in half of the trials, and the face images shared the same peripheral locations in their study. Therefore, observers might have had an incentive to monitor those peripheral locations and distractors that fell in that location. The present study differed from these previous studies in that we examined conditions under which faces were totally irrelevant to the experimental task. The present study directly investigated whether faces capture attention regardless of endogenously established attentional set. The results demonstrate that
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faces are special in terms of attentional capture and can overcome the control of attentional set in that completely task-irrelevant faces, regardless of attractiveness, were able to break through a top-down attentional set given a brief distractor-target SOA. Acknowledgments This study was supported by Grant-in-Aid for Scientific Research on Innovative Areas, ‘‘Face perception and recognition’’ from MEXT KAKENHI 23119731 to JK. We thank Shoko Kanaya for her helpful comments on this work.
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