Psychological Research DOI 10.1007/s00426-014-0640-y
ORIGINAL ARTICLE
The influence of attention toward facial expressions on size perception Jeong-Won Choi • Kiho Kim • Jang-Han Lee
Received: 23 February 2014 / Accepted: 11 December 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract According to the New Look theory, size perception is affected by emotional factors. Although previous studies have attempted to explain the effects of both emotion and motivation on size perception, they have failed to identify the underlying mechanisms. This study aimed to investigate the underlying mechanisms of size perception by applying attention toward facial expressions using the Ebbinghaus illusion as a measurement tool. The participants, female university students, were asked to judge the size of a target stimulus relative to the size of facial expressions (i.e., happy, angry, and neutral) surrounding the target. The results revealed that the participants perceived angry and neutral faces to be larger than happy faces. This finding indicates that individuals pay closer attention to neutral and angry faces than happy ones. These results suggest that the mechanisms underlying size perception involve cognitive processes that focus attention toward relevant stimuli and block out irrelevant stimuli.
Introduction The recognition of an object involves a subjective, rather than objective, perception of size relative to the size of surrounding objects. Size perception is known to be affected by physical factors, such as length, height, and J.-W. Choi K. Kim J.-H. Lee (&) Department of Psychology, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 156-756, Korea e-mail: [email protected] J.-W. Choi e-mail: [email protected] K. Kim e-mail: [email protected]
volume, as well as psychological factors, including emotion and motivation. The New Look theory describes the effect of emotional factors on size perception and suggests that perceptual processing, such as the judgment of size, depends on whether the stimulus is effectively loaded and other emotional variables (van Ulzen, Semin, Oudejans, & Beek, 2008). For example, poor children were more likely to perceive coins as being larger than cardboard discs of the same size than rich children were (Bruner & Danilova, 1947). Among positive (dollar sign), neutral (square), and negative (swastika) symbols, subjects overestimated the size of the symbols with positive and negative valence compared with neutral symbols (Bruner & Postman, 1948). Emotional stimuli are perceived as larger than neutral stimuli due to embodied cognition. In embodied cognition, our visual system is affected by various factors, especially emotional states, intention of behavior and biological needs, depending on the context (Proffitt, Stefanucci, Banton, & Epstein, 2003; van Ulzen et al., 2008). However, although the New Look theory has identified the effect of emotional factors on size perception, it could not explain the direction of the perception of positive stimuli (i.e., whether it is perceived as large or small) or the result for negative stimuli. Therefore, it has been unable to identify the underlying mechanisms by which emotion affects size perception. Several researchers have applied motivational factors to uncover the mechanisms underlying size perception. Studies have shown that individuals with motivation toward a particular stimulus perceive the stimulus to be larger than the size perceived by individuals without motivation (Brendl, Markman, & Messner, 2003; Veltkamp, Aarts, & Custers, 2008). For example, smokers have a tendency to perceive cigarettes as being longer than they are (Brendl et al., 2003). In addition, persons who are
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thirsty judge a glass of water to be larger than persons who are not thirsty do (Veltkamp et al., 2008). These results show that size perception could be explained by motivational factors. Although the researchers found that both motivational and emotional factors are relevant to size perception, they could not explain how those factors fit into the mechanism of size perception. A cognitive model was proposed to explain the effect of motivation on perceptual processing (Gable & Harmon-Jones, 2010). Motivation has been classified into two types: approach and avoidance motivation (Elliot, 2006). Although these motivational factors represent different directions of behavior with respect to goal attainment, these factors equally activate the cognitive processes that underlie goal-seeking behaviors. Regardless of the direction of motivation, increasing motivation toward a target provokes cognitive processes that concurrently focus attention toward relevant stimuli and block out irrelevant stimuli. Therefore, the stimulus attracting selective attention would be perceived as larger than an unattractive stimulus would. Increasing the motivation toward an object triggers selective attention, which leads to the perception of a larger size. The ability to selectively assign attention to stimuli that have motivational significance is an evolutionary mechanism that has been developed to adapt and cope with significant information within the environment. This study investigated the effect of attentional factors on size perception using facial expressions that are commonly used in attention-related studies. Prior studies have reported that emotional expressions might facilitate the detection and orientation of attention to faces, as some emotion-related information can be perceived implicitly outside of conscious awareness and tends to attract attention (Roskos-Ewoldsen & Fazio, 1992; Esteves, Dimberg, & Ohman, 1994; Bradley et al., 1997). In particular, angry faces capture more attention than happy faces (Eastwood, Smilek, & Merikle, 2003; Juth, Lundqvist, Karlsson, & Ohman, 2005; Pinkham, Griffin, Baron, Sasson, & Gur, 2010). Negative stimuli, such as anger and fear, are evolutionarily learned stimuli and have a prominent influence on perceptual processing to enhance attention (Cannon, 1929). Facial expressions also provide higher ecological validity than other stimulus types because facial expressions convey social information, including cues to interpret the responses of others, which facilitates decision-making in social interactions (Ekman, 1982; Izard & Bartlett, 1972; Knutson, 1996; Plutchik, 1980; Planalp, DeFrancisco, & Rutherford, 1996). Thus, the current study used three facial stimuli: an angry face, which is widely known to attract the most attention; a happy face, which is widely known to attract less attention than an angry face; and a neutral face as a control stimulus.
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To reasonably examine size perception, this study used the Ebbinghaus illusion to measure size perception. The Ebbinghaus illusion is a phenomenon in which individuals routinely overestimate the size of a central target circle that is surrounded by smaller circles compared with a central target circle surrounded by larger circles. This phenomenon occurs despite the fact that the size of the central target circle never changes (Stapel & Koomen, 1997). Studies that have measured size perception with the Ebbinghaus illusion have used illustrations, figures, and pictures of objects or animals as stimuli (Coren, 1971; Coren & Enns, 1993; Coren & Girgus, 1978; Stapel & Koomen, 1997; van Ulzen et al., 2008). The surrounding circles in the Ebbinghaus illusion draw attention away from the central target circle. If the surrounding circles attract attention and are perceived to be large, then the size of the central target circle subjectively decreases. The shape of the original Ebbinghaus illusion was modified in this study by inserting facial expressions in the surrounding circles. Because the central target circle remained blank, the judgment of the size of the central target circle was distracted by the facial expressions. If an individual’s attention toward the surrounding circles is diverted (i.e., the surrounding circles are perceived to be larger than the central target circle), he or she will indicate that the central circle is relatively small. The current study aimed to examine the effects of both the size of the surrounding circles as well as the facial expressions (i.e., happy, angry, and neutral faces) on size perception using the Ebbinghaus illusion. In addition, this study aimed to describe the mechanism of size perception based on attentional factors.
Methods Participants Prior to the experiment, 368 female undergraduate students from Chung-ang University in Seoul, Korea, completed the Social Avoidance and Distress Scale (SADS; Watson & Friend, 1969) and Beck Depression Inventory (BDI; Beck, Ward, Mendelson, Mock, & Erbaugh, 1961). To screen the normal student group with both questionnaires, 30 persons (mean age 20.63 years, SD 1.57, range 18–24 years) with scores within ±1 SD of the mean score on the SADS (M = 75.97, SD = 3.45) and lower than 10 on the BDI (M = 4.93, SD = 2.64) were selected as participants. These inclusion criteria were used to ensure that only participants without depressive symptoms were included in the study. All of the participants provided written informed consent to participate in this study and received a modest monetary compensation after the experiment.
Psychological Research
Self-report inventory The Social Avoidance and Distress Scale (SADS; Watson & Friend, 1969) is a self-report inventory that measures two aspects of social anxiety: the level of anxiety or distress associated with social interaction and the level of avoidance of social situations. The SADS includes 28 items that are rated on a 5-point scale from 1 (not at all) to 5 (very much so). The total scores on the SADS range from 28 to 140 points, and higher scores indicate a greater level of social anxiety. Cronbach’s a in this study was 0.83. The Beck Depression Inventory (BDI; Beck et al., 1961) is a self-report inventory that measures the severity of depression. The BDI is composed of 21 items related to physical and cognitive symptoms of depression. Each item is rated on a 4-point scale from 0 to 3, and the total scores range from 0 to 63. Cut-off scores were determined such that a total score of 0–9 was considered minimal, 10–18 mild, 19–29 moderate, and 30–63 severe depression. Cronbach’s a in this study was 0.84. The State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, & Lushene, 1970) is a self-report inventory that consists of two subscales, state anxiety and trait anxiety, with 20 items each. Each item is rated on a 4-point Likert scale from 1 (not at all) to 4 (very much so). Scores range from 20 to 80 on each subscale, and higher scores indicate a greater level of anxiety. In this study, the Korean version of the STAI was used, and state anxiety (STAI-S) was measured both pre- and post-task to evaluate changes in state anxiety levels. Cronbach’s a in this study was 0.83 for state anxiety and 0.86 for trait anxiety. Materials For the stimuli used in the modified Ebbinghaus illusion, we extracted facial expressions from the Korea University Facial Expression Collection (KUFEC; Lee, Lee, Lee, Choi, & Kim, 2006). To verify the validity and reliability of the selected stimuli, 24 students rated the valence, arousal, and accuracy of the emotional category for each facial expression. The final set of stimuli used in the experiment included three types of facial expressions (i.e., happy, angry, and neutral) from two female models. The stimuli used in the original Ebbinghaus illusion are round circles of the same diameter. However, for the modified Ebbinghaus illusion that was used in this study, the round circles were changed to ovals to accommodate the shape of the facial stimuli. The faces were manipulated using grayscale and omitting bangs to control for other factors that may influence size perception. The size of the stimuli that were used in a previous study (Stapel & Koomen, 1997) was modified for this study through pilot tests. The horizontal diameter of the target
circle was maintained at 2.2 cm in our study. However, the initial sizes of the large and small surrounding circles were too small to permit an accurate perception of the emotion of the facial expressions. Therefore, the large surrounding circles were reduced to a horizontal diameter of 3 cm and the small surrounding circles were enlarged to a horizontal diameter of 1.5 cm to allow the facial expressions to be observed clearly. The distance between the target circle and surrounding circles for large circles was 1.03 cm, that between the target circle and surrounding circles for small circles was 2.8 cm, and that between surrounding circles for both small and large circles was 1.6 cm. Size comparison task Unlike in the original Ebbinghaus illusion, in which the stimulus on one side of the screen shows small circles surrounding a central target circle and the stimulus on the other side of the screen presents an image surrounded by large surrounding circles, the pairs in our experiment were modified such that the size of the surrounding stimulus was the same on both sides to compare the attributes of the stimuli (i.e., the attentional intensity in our study) rather than the size of the surrounding circles (see Fig. 1). Therefore, two conditions were established in this task based on the size of the stimuli: large surrounding circles (large condition) and small surrounding circles (small condition). Large stimuli were presented on both sides in the large condition, and small stimuli were presented on both sides in the small condition. The facial pairs, Happy–Angry, Angry–Neutral, and Neutral–Happy, were presented on one screen at the same time. The facial pairs were presented in a counterbalanced order between the left and right sides of the screen. Stimuli were also presented at different locations on the screen (up and down) to prevent persistence of vision. The facial pair and size conditions were presented in a randomized order. The task consisted of 192 trials, half of which were catch trials that contained surrounding circles of different sizes on both stimuli sides. The 192 trials were performed in two blocks. The first block was initiated after 10 practice trials. Participants were instructed to observe the screen carefully when the two stimuli pairs were presented and asked to push one of three arrow keys (i.e., right, left, or up) to record their response. Participants were instructed to push the right arrow key if the right target circle seemed to be larger than the left target circle, the left arrow if they felt the reverse to be true, and the upward arrow key if the two target circles seemed to be the same size. The stimuli of a trial were presented until the participant responded. Catch trials were excluded from data analysis because surrounding circles containing different sizes result in normal perceptual illusion, EI, regardless of the contents (i.e., facial expressions).
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Psychological Research Fig. 1 An example of stimuli presented in time and order
Procedures The experiment was conducted in a quiet laboratory, and each participant completed the task individually. When participants arrived at the laboratory, they were asked to complete the consent form and the STAI-S first. Next, the participants were provided with instructions about the size comparison task and the method. Their faces were then fixed at a distance of 60 cm from the monitor using a fixation tool. Participants then performed the task (including a 5-min break). After the task was completed, the participants were asked to complete the STAI-S again. Lastly, the participants were debriefed on the task and received approximately three dollars as a monetary reward.
separately for each size condition. A higher value of this index, which represents a higher number of ‘large’ responses for the central target circle, indicates that participants perceived the facial stimuli within the surrounding circles as small. To confirm differences in size perception relative to the three facial pairs and the two surrounding circle sizes, a 3 (facial pair: H-A, A-N, N-H) 9 2 (surrounding circle size: large, small) repeated measures analysis of variance (ANOVA) was conducted. For additional analysis, a paired t test was conducted to compare size perceptions within facial pairs. All data were analyzed with SPSS 17.0 for Windows, and a Greenhouse–Geisser correction was applied to correct for multiple comparisons.
Apparatus Results The size comparison task was presented using E-Prime 2.0 (Psychological Software Tool; Pittsburgh, PA, USA) on a desktop computer with a 1900 monitor set at a resolution of 1,024 9 768 pixels. The participants’ faces were fixed at a distance of 60 cm from the monitor using a fixation tool. Data analysis To investigate the patterns of size perception relative to the attention induced by the facial expressions, the data from the size comparison task were used to calculate an index of the ratio of the differences in responses for each facial pair. The index was calculated by dividing the sum of the number of times the participants responded with ‘large’ for a particular facial stimulus by the sum of the trials in which that facial stimulus appeared. This index was computed
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Self-questionnaires The scores on the STAI-S pre- and post-task were compared to determine changes in state anxiety level. There was no significant difference between pre- (M = 40.40, SD = 8.81) and post-task (M = 42.83, SD = 9.72, t(29) = -1.30, MSE = 0.76, n.s.) state anxiety levels. This result indicates that state anxiety was not provoked by this task. Size comparison task A 3 (facial pair: Happy-Angry, Angry-Neutral, NeutralHappy) 9 2 (surrounding circle size: large, small) repeated measures ANOVA was conducted to examine the effect of attention induced by facial expressions on size perception.
Psychological Research
A significant main effect for surrounding circle size was observed (F(1, 29) = 13.35, MSE = 130.58, p \ 0.01, g2p = 0.28). This result indicates that the central target circle was perceived as large when the surrounding circles were small compared to the size perceived when the surrounding circles were large. A significant effect for facial pairing (F(1.65, 56.18) = 18.93, MSE = 209.66, p \ 0.01, g2p = 0.36) was also observed such that angry faces captured more attention than happy ones and neutral faces captured more attention than happy ones. The results showed a significant effect of interaction between the surrounding circles and facial stimulus (F(1.68, 57.22) = 4.01, MSE = 15.62, p \ 0.05, g2p = 0.11). This result indicates that the effect of facial expression on size perception varied by the size of the surrounding circles. For additional analysis, a paired t test was conducted to compare the differences in the pattern of size perception for each facial pair within each size condition (Fig. 2). The results were significant for the Happy–Angry pairs for small surrounding circles, t(34) = 2.84, MSE = 0.69, p \ 0.01, and large surrounding circles, t(34) = 4.97, MSE = 70, p \ 0.01; and for the Happy-Neutral pairs for small surrounding circles, t(34) = 2.75, MSE = 0.79, p = 0.01, and large surrounding circles, t(34) = 5.51, MSE = 0.65, p \ 0.01. These results indicate that participants perceived the angry faces as large in the Happy– Angry pairs and neutral faces as large in the Happy–Neutral pairs. These results also suggest that this pattern of size perception was similar for both size conditions. However, no significant result was observed for the Angry–Neutral pairs in either size condition, preventing us from identifying a difference in size perception for angry versus neutral faces.
Discussion The current study aimed to examine the effect of attention induced by facial expressions on size perception using a modified Ebbinghaus illusion as a measurement tool. The result suggests that the perception of the central target circle as large means that the size of the surrounding circles was perceived as small relative to the central target circle. This might indicate that the facial stimuli that were contained within the surrounding circles attracted little attention. In contrast, the perception of the central target circle as small might means that the surrounding circles were perceived as large relative to the central target circle. This might indicate that the facial stimuli that were contained within the surrounding circles attracted greater attention. In the current task, the central target circles were blank, and the surrounding circles contained facial expressions. Thus, the facial expressions to which the participants paid more attention could be identified by comparing the facial pairs presented on the two sides of the screen. The results from this study showed that the angry faces led to an overestimation of size relative to the happy faces in the Happy–Angry pairs. This result suggested that the angry faces attracted more attention than the happy faces, in agreement with previous studies that found that angry faces attract more attention than happy faces (Eastwood et al., 2003; Juth et al., 2005; Pinkham et al., 2010). This result indicated that individuals would be more susceptible to angry faces than happy faces. Interestingly, the results of the Neutral–Happy pairs revealed that participants perceived the neutral faces as larger than the happy faces, which indicates that the neutral faces attracted more attention than the happy faces. Additionally, there was no statistically significant
Fig. 2 Ratio of response differences for each facial pair in small and large conditions
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difference between the neutral faces and the angry faces in the Neutral–Angry pairs. One interpretation of these results is that participants perceived both neutral faces and angry faces as negative facial expressions. Therefore, both neutral and angry faces may attract more attention than happy faces. These results are consistent with previous studies that found that neutral faces may be evaluated negatively as angry faces depending on social norms or investigators’ expectations (Parrot & Hertel, 1999). Another purpose of this study was to examine attentional resource allocation with respect to size perception using the Ebbinghaus illusion that has been supported by a series of assumptions. To this end, size comparison tasks were performed with the facial expressions attracting attention. According to the New Look theory, happy and angry faces are perceived as larger than neutral faces. However, according to the principle that describes the effect of motivation on size perception, happy faces should be perceived as larger than angry or neutral faces. The results of the current study showed that both the angry and neutral faces were perceived as larger than the happy faces, in disagreement with both explanations. This result might indicate that negative stimuli attract more attention than positive stimuli, as has been reported in several studies (Eastwood et al., 2003; Juth et al., 2005; Pinkham et al., 2010). Therefore, negative stimuli may enhance attention to a greater extent than positive stimuli, leading to a larger perceived size of negative stimuli. The results of this study can explain some of the mechanisms underlying size perception. In this study, we used attention-inducing stimuli combined with attentiondistracting stimuli in the Ebbinghaus illusion task. We confirmed that emotion-related information can attract attention and alter size perception. Based on the importance of facial expressions in social interactions, the perception of an object’s size as large may be an adaptive strategy that can be easily implemented in a social environment (Veltkamp et al., 2008). Therefore, the fact that negative faces are perceived as larger than happy faces indicates that people are more affected by angry faces than happy faces, which may suggest a strategy for coping with negative feedback in social circumstances by focusing attention on negative stimuli (Cannon, 1929). This study also attempted to explain the allocation of attentional resources using the Ebbinghaus illusion as a measurement tool based on a series of assumptions. Although the size of the surrounding circles was modified from the original Ebbinghaus illusion and facial expressions were applied as the stimuli, the results replicated the visual illusion of the original Ebbinghaus illusion. When pairs of facial expressions were compared, the central target circle was perceived as larger in the small condition than in the large condition. This result indicates that the large condition is
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more appropriate when measuring attention to facial expressions with the Ebbinghaus illusion because it ensures that the stimuli will be clearly recognized. However, because similar patterns of size perception with facial expressions appeared in both size conditions, these results show that the visual illusion was maintained despite a modification of the shape of the Ebbinghaus illusion and the use of facial expressions as stimuli. These results also suggest that the Ebbinghaus illusion is an appropriate tool for measuring attention. Although we investigated the mechanism of size perception using attentional factors, there are some limitations to this study. First, our paradigm consisted of an indirect measurement of attention toward stimuli without measuring the real allocation of attention or cognitive processes. Therefore, further studies should consider a manipulation task that assesses attentional patterns of the stimuli using an eyetracker or other instrumentation. Second, we used only a few types of positive and negative facial expressions. Further studies should investigate not only the effect of other types of facial expressions on size perception but also the effect of other types of emotional stimuli on size perception. Lastly, only female participants were included in this experiment. Furthermore, only female faces were included as the task stimuli because responses to the facial emotions of the same and opposite gender may differ. Thus, further research is required to replicate the experiment using both male and female models as well as male and female participants. Despite these limitations, this study empirically examined the mechanisms of emotion-induced attention with respect to size perception. Through this paradigm of size perception, our results suggest which facial expressions allocate more attention within the context of social interactions. The development of a measure that can determine whether an individual is able to focus his or her attention on relevant stimuli and ignore irrelevant stimuli may be helpful in the treatment of individuals who have difficulty with social interactions.
References Beck, A. T., Ward, C. H., Mendelson, M., Mock, J., & Erbaugh, J. (1961). An inventory for measuring depression. Archives of General Psychiatry, 4, 561–571. Bradley, B. P., Mogg, K., Millar, N., Bonham-Carter, C., Fergusson, E., Jenkins, J., & Parr, M. (1997). Attentional bias for emotional faces. Cognition and Emotion, 11, 25–42. Brendl, C. M., Markman, A. B., & Messner, C. (2003). The devaluation effect: Activating a need devalues unrelated objects. Journal of Consumer Research, 29, 463–473. Bruner, J. S., & Danilova, M. V. (1947). Value and need as organizing factors in perception. Journal of Abnormal and Social Psychology, 42, 33–44.
Psychological Research Bruner, J. S., & Postman, L. (1948). Symbolic value as an organizing factor in perception. Journal of Social Psychology, 27, 203–208. Cannon, W. B. (1929). Bodily changes in pain, hunger, fear, and rage. New York: Littleton. Coren, S. (1971). A size contrast illusion without physical size difference. American Journal of Psychology, 84, 565–566. Coren, S., & Enns, J. T. (1993). Size contrast as a function of conceptual similarity between test and inducers. Perception and Psychophysics, 54, 579–588. Coren, S., & Girgus, J. S. (1978). Seeing is deceiving: The psychology of visual illusions. Hillsdale: Lawrence Erlbaum Associates. Eastwood, J. D., Smilek, D., & Merikle, P. M. (2003). Negative facial expression captures attention and disrupts performance. Attention, Perception, & Psychophysics, 65, 352–358. Ekman, P. (1982). Emotion in the human face (2nd ed.). Cambridge: University of Cambridge Press. Elliot, A. J. (2006). The hierarchical model of approach-avoidance motivation. Motivation and Emotion, 30, 111–116. ¨ hman, A. (1994). Automatically elicited Esteves, F., Dimberg, U., & O fear: Conditioned skin conductance responses to masked facial expressions. Cognition and Emotion, 9, 99–108. Gable, P. A., & Harmon-Jones, E. (2010). The effect of low versus high approach-motivated positive affect on memory for peripherally versus centrally presented information. Emotion, 10, 599–603. Izard, C. E., & Bartlett, E. S. (1972). Patterns of emotions: A new analysis of anxiety and depression. Oxford: Academic Press. Juth, P., Lundqvist, D., Karlsson, A., & Ohman, A. (2005). Looking for foes and friends: Perceptual and emotional factors when finding a face in the crowd. Emotion, 5, 379–395. Knutson, B. (1996). Facial expressions of emotion influence interpersonal trait inferences. Journal of Nonverbal Behavior, 20, 165–182. Lee, T. H., Lee, K., Lee, K. Y., Choi, J. S., & Kim, H. T. (2006). Korea University facial expression collection: KUFEC. Seoul: Lab of Behavioral Neuroscience, Department of Psychology, Korea University.
Parrot, W. G., & Hertel, P. (1999). Research methods in cognition and emotion. In T. Dalgleish & M. Power (Eds.), Handbook of cognition and emotion (pp. 61–81). New York: John Wiley & Sons Ltd. Pinkham, A. E., Griffin, M., Baron, R., Sasson, N. J., & Gur, R. C. (2010). The face in the crowd effect: Anger superiority when using real faces and multiple identities. Emotion, 10, 141. Planalp, S., DeFrancisco, V. L., & Rutherford, D. (1996). Varieties of cues to emotion in naturally occurring situations. Cognition and Emotion, 10, 137–153. Plutchik, R. A. (1980). Emotion: A psychoevolutionary synthesis. New York: Harper & Row. Proffitt, D. A., Stefanucci, J., Banton, T., & Epstein, W. (2003). The role of effort in perceiving distance. Psychological Science, 14(2), 106–112. Roskos-Ewoldsen, D. R., & Fazio, R. H. (1992). On the orienting value of attitudes: Attitude accessibility as a determinant of an object’s attraction of visual attention. Journal of Personality and Social Psychology, 63, 198–211. Spielberger, C. D., Gorsuch, R. L., & Lushene, R. E. (1970). Manual for the State-Trait Anxiety Inventory. Palo Alto: Consulting Psychologists Press. Stapel, D. A., & Koomen, W. (1997). Social categorization and perceptual judgment of size: When perception is social. Journal of Personality and Social Psychology, 73, 1177–1190. van Ulzen, N. R., Semin, G. R., Oudejans, R. R. D., & Beek, P. J. (2008). Affective stimulus properties influence size perception and the Ebbinghaus illusion. Psychological Research, 72, 304–310. Veltkamp, M., Aarts, H., & Custers, R. (2008). Perception in the service of goal pursuit: Motivation to attain goals enhances the perceived size of goal-instrumental objects. Social Cognition, 26, 720–736. Watson, D., & Friend, R. (1969). Measurement of social-evaluative anxiety. Journal of Consulting and Clinical Psychology, 33, 448–457.
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ORIGINAL ARTICLE
The influence of attention toward facial expressions on size perception Jeong-Won Choi • Kiho Kim • Jang-Han Lee
Received: 23 February 2014 / Accepted: 11 December 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract According to the New Look theory, size perception is affected by emotional factors. Although previous studies have attempted to explain the effects of both emotion and motivation on size perception, they have failed to identify the underlying mechanisms. This study aimed to investigate the underlying mechanisms of size perception by applying attention toward facial expressions using the Ebbinghaus illusion as a measurement tool. The participants, female university students, were asked to judge the size of a target stimulus relative to the size of facial expressions (i.e., happy, angry, and neutral) surrounding the target. The results revealed that the participants perceived angry and neutral faces to be larger than happy faces. This finding indicates that individuals pay closer attention to neutral and angry faces than happy ones. These results suggest that the mechanisms underlying size perception involve cognitive processes that focus attention toward relevant stimuli and block out irrelevant stimuli.
Introduction The recognition of an object involves a subjective, rather than objective, perception of size relative to the size of surrounding objects. Size perception is known to be affected by physical factors, such as length, height, and J.-W. Choi K. Kim J.-H. Lee (&) Department of Psychology, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 156-756, Korea e-mail: [email protected] J.-W. Choi e-mail: [email protected] K. Kim e-mail: [email protected]
volume, as well as psychological factors, including emotion and motivation. The New Look theory describes the effect of emotional factors on size perception and suggests that perceptual processing, such as the judgment of size, depends on whether the stimulus is effectively loaded and other emotional variables (van Ulzen, Semin, Oudejans, & Beek, 2008). For example, poor children were more likely to perceive coins as being larger than cardboard discs of the same size than rich children were (Bruner & Danilova, 1947). Among positive (dollar sign), neutral (square), and negative (swastika) symbols, subjects overestimated the size of the symbols with positive and negative valence compared with neutral symbols (Bruner & Postman, 1948). Emotional stimuli are perceived as larger than neutral stimuli due to embodied cognition. In embodied cognition, our visual system is affected by various factors, especially emotional states, intention of behavior and biological needs, depending on the context (Proffitt, Stefanucci, Banton, & Epstein, 2003; van Ulzen et al., 2008). However, although the New Look theory has identified the effect of emotional factors on size perception, it could not explain the direction of the perception of positive stimuli (i.e., whether it is perceived as large or small) or the result for negative stimuli. Therefore, it has been unable to identify the underlying mechanisms by which emotion affects size perception. Several researchers have applied motivational factors to uncover the mechanisms underlying size perception. Studies have shown that individuals with motivation toward a particular stimulus perceive the stimulus to be larger than the size perceived by individuals without motivation (Brendl, Markman, & Messner, 2003; Veltkamp, Aarts, & Custers, 2008). For example, smokers have a tendency to perceive cigarettes as being longer than they are (Brendl et al., 2003). In addition, persons who are
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thirsty judge a glass of water to be larger than persons who are not thirsty do (Veltkamp et al., 2008). These results show that size perception could be explained by motivational factors. Although the researchers found that both motivational and emotional factors are relevant to size perception, they could not explain how those factors fit into the mechanism of size perception. A cognitive model was proposed to explain the effect of motivation on perceptual processing (Gable & Harmon-Jones, 2010). Motivation has been classified into two types: approach and avoidance motivation (Elliot, 2006). Although these motivational factors represent different directions of behavior with respect to goal attainment, these factors equally activate the cognitive processes that underlie goal-seeking behaviors. Regardless of the direction of motivation, increasing motivation toward a target provokes cognitive processes that concurrently focus attention toward relevant stimuli and block out irrelevant stimuli. Therefore, the stimulus attracting selective attention would be perceived as larger than an unattractive stimulus would. Increasing the motivation toward an object triggers selective attention, which leads to the perception of a larger size. The ability to selectively assign attention to stimuli that have motivational significance is an evolutionary mechanism that has been developed to adapt and cope with significant information within the environment. This study investigated the effect of attentional factors on size perception using facial expressions that are commonly used in attention-related studies. Prior studies have reported that emotional expressions might facilitate the detection and orientation of attention to faces, as some emotion-related information can be perceived implicitly outside of conscious awareness and tends to attract attention (Roskos-Ewoldsen & Fazio, 1992; Esteves, Dimberg, & Ohman, 1994; Bradley et al., 1997). In particular, angry faces capture more attention than happy faces (Eastwood, Smilek, & Merikle, 2003; Juth, Lundqvist, Karlsson, & Ohman, 2005; Pinkham, Griffin, Baron, Sasson, & Gur, 2010). Negative stimuli, such as anger and fear, are evolutionarily learned stimuli and have a prominent influence on perceptual processing to enhance attention (Cannon, 1929). Facial expressions also provide higher ecological validity than other stimulus types because facial expressions convey social information, including cues to interpret the responses of others, which facilitates decision-making in social interactions (Ekman, 1982; Izard & Bartlett, 1972; Knutson, 1996; Plutchik, 1980; Planalp, DeFrancisco, & Rutherford, 1996). Thus, the current study used three facial stimuli: an angry face, which is widely known to attract the most attention; a happy face, which is widely known to attract less attention than an angry face; and a neutral face as a control stimulus.
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To reasonably examine size perception, this study used the Ebbinghaus illusion to measure size perception. The Ebbinghaus illusion is a phenomenon in which individuals routinely overestimate the size of a central target circle that is surrounded by smaller circles compared with a central target circle surrounded by larger circles. This phenomenon occurs despite the fact that the size of the central target circle never changes (Stapel & Koomen, 1997). Studies that have measured size perception with the Ebbinghaus illusion have used illustrations, figures, and pictures of objects or animals as stimuli (Coren, 1971; Coren & Enns, 1993; Coren & Girgus, 1978; Stapel & Koomen, 1997; van Ulzen et al., 2008). The surrounding circles in the Ebbinghaus illusion draw attention away from the central target circle. If the surrounding circles attract attention and are perceived to be large, then the size of the central target circle subjectively decreases. The shape of the original Ebbinghaus illusion was modified in this study by inserting facial expressions in the surrounding circles. Because the central target circle remained blank, the judgment of the size of the central target circle was distracted by the facial expressions. If an individual’s attention toward the surrounding circles is diverted (i.e., the surrounding circles are perceived to be larger than the central target circle), he or she will indicate that the central circle is relatively small. The current study aimed to examine the effects of both the size of the surrounding circles as well as the facial expressions (i.e., happy, angry, and neutral faces) on size perception using the Ebbinghaus illusion. In addition, this study aimed to describe the mechanism of size perception based on attentional factors.
Methods Participants Prior to the experiment, 368 female undergraduate students from Chung-ang University in Seoul, Korea, completed the Social Avoidance and Distress Scale (SADS; Watson & Friend, 1969) and Beck Depression Inventory (BDI; Beck, Ward, Mendelson, Mock, & Erbaugh, 1961). To screen the normal student group with both questionnaires, 30 persons (mean age 20.63 years, SD 1.57, range 18–24 years) with scores within ±1 SD of the mean score on the SADS (M = 75.97, SD = 3.45) and lower than 10 on the BDI (M = 4.93, SD = 2.64) were selected as participants. These inclusion criteria were used to ensure that only participants without depressive symptoms were included in the study. All of the participants provided written informed consent to participate in this study and received a modest monetary compensation after the experiment.
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Self-report inventory The Social Avoidance and Distress Scale (SADS; Watson & Friend, 1969) is a self-report inventory that measures two aspects of social anxiety: the level of anxiety or distress associated with social interaction and the level of avoidance of social situations. The SADS includes 28 items that are rated on a 5-point scale from 1 (not at all) to 5 (very much so). The total scores on the SADS range from 28 to 140 points, and higher scores indicate a greater level of social anxiety. Cronbach’s a in this study was 0.83. The Beck Depression Inventory (BDI; Beck et al., 1961) is a self-report inventory that measures the severity of depression. The BDI is composed of 21 items related to physical and cognitive symptoms of depression. Each item is rated on a 4-point scale from 0 to 3, and the total scores range from 0 to 63. Cut-off scores were determined such that a total score of 0–9 was considered minimal, 10–18 mild, 19–29 moderate, and 30–63 severe depression. Cronbach’s a in this study was 0.84. The State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, & Lushene, 1970) is a self-report inventory that consists of two subscales, state anxiety and trait anxiety, with 20 items each. Each item is rated on a 4-point Likert scale from 1 (not at all) to 4 (very much so). Scores range from 20 to 80 on each subscale, and higher scores indicate a greater level of anxiety. In this study, the Korean version of the STAI was used, and state anxiety (STAI-S) was measured both pre- and post-task to evaluate changes in state anxiety levels. Cronbach’s a in this study was 0.83 for state anxiety and 0.86 for trait anxiety. Materials For the stimuli used in the modified Ebbinghaus illusion, we extracted facial expressions from the Korea University Facial Expression Collection (KUFEC; Lee, Lee, Lee, Choi, & Kim, 2006). To verify the validity and reliability of the selected stimuli, 24 students rated the valence, arousal, and accuracy of the emotional category for each facial expression. The final set of stimuli used in the experiment included three types of facial expressions (i.e., happy, angry, and neutral) from two female models. The stimuli used in the original Ebbinghaus illusion are round circles of the same diameter. However, for the modified Ebbinghaus illusion that was used in this study, the round circles were changed to ovals to accommodate the shape of the facial stimuli. The faces were manipulated using grayscale and omitting bangs to control for other factors that may influence size perception. The size of the stimuli that were used in a previous study (Stapel & Koomen, 1997) was modified for this study through pilot tests. The horizontal diameter of the target
circle was maintained at 2.2 cm in our study. However, the initial sizes of the large and small surrounding circles were too small to permit an accurate perception of the emotion of the facial expressions. Therefore, the large surrounding circles were reduced to a horizontal diameter of 3 cm and the small surrounding circles were enlarged to a horizontal diameter of 1.5 cm to allow the facial expressions to be observed clearly. The distance between the target circle and surrounding circles for large circles was 1.03 cm, that between the target circle and surrounding circles for small circles was 2.8 cm, and that between surrounding circles for both small and large circles was 1.6 cm. Size comparison task Unlike in the original Ebbinghaus illusion, in which the stimulus on one side of the screen shows small circles surrounding a central target circle and the stimulus on the other side of the screen presents an image surrounded by large surrounding circles, the pairs in our experiment were modified such that the size of the surrounding stimulus was the same on both sides to compare the attributes of the stimuli (i.e., the attentional intensity in our study) rather than the size of the surrounding circles (see Fig. 1). Therefore, two conditions were established in this task based on the size of the stimuli: large surrounding circles (large condition) and small surrounding circles (small condition). Large stimuli were presented on both sides in the large condition, and small stimuli were presented on both sides in the small condition. The facial pairs, Happy–Angry, Angry–Neutral, and Neutral–Happy, were presented on one screen at the same time. The facial pairs were presented in a counterbalanced order between the left and right sides of the screen. Stimuli were also presented at different locations on the screen (up and down) to prevent persistence of vision. The facial pair and size conditions were presented in a randomized order. The task consisted of 192 trials, half of which were catch trials that contained surrounding circles of different sizes on both stimuli sides. The 192 trials were performed in two blocks. The first block was initiated after 10 practice trials. Participants were instructed to observe the screen carefully when the two stimuli pairs were presented and asked to push one of three arrow keys (i.e., right, left, or up) to record their response. Participants were instructed to push the right arrow key if the right target circle seemed to be larger than the left target circle, the left arrow if they felt the reverse to be true, and the upward arrow key if the two target circles seemed to be the same size. The stimuli of a trial were presented until the participant responded. Catch trials were excluded from data analysis because surrounding circles containing different sizes result in normal perceptual illusion, EI, regardless of the contents (i.e., facial expressions).
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Psychological Research Fig. 1 An example of stimuli presented in time and order
Procedures The experiment was conducted in a quiet laboratory, and each participant completed the task individually. When participants arrived at the laboratory, they were asked to complete the consent form and the STAI-S first. Next, the participants were provided with instructions about the size comparison task and the method. Their faces were then fixed at a distance of 60 cm from the monitor using a fixation tool. Participants then performed the task (including a 5-min break). After the task was completed, the participants were asked to complete the STAI-S again. Lastly, the participants were debriefed on the task and received approximately three dollars as a monetary reward.
separately for each size condition. A higher value of this index, which represents a higher number of ‘large’ responses for the central target circle, indicates that participants perceived the facial stimuli within the surrounding circles as small. To confirm differences in size perception relative to the three facial pairs and the two surrounding circle sizes, a 3 (facial pair: H-A, A-N, N-H) 9 2 (surrounding circle size: large, small) repeated measures analysis of variance (ANOVA) was conducted. For additional analysis, a paired t test was conducted to compare size perceptions within facial pairs. All data were analyzed with SPSS 17.0 for Windows, and a Greenhouse–Geisser correction was applied to correct for multiple comparisons.
Apparatus Results The size comparison task was presented using E-Prime 2.0 (Psychological Software Tool; Pittsburgh, PA, USA) on a desktop computer with a 1900 monitor set at a resolution of 1,024 9 768 pixels. The participants’ faces were fixed at a distance of 60 cm from the monitor using a fixation tool. Data analysis To investigate the patterns of size perception relative to the attention induced by the facial expressions, the data from the size comparison task were used to calculate an index of the ratio of the differences in responses for each facial pair. The index was calculated by dividing the sum of the number of times the participants responded with ‘large’ for a particular facial stimulus by the sum of the trials in which that facial stimulus appeared. This index was computed
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Self-questionnaires The scores on the STAI-S pre- and post-task were compared to determine changes in state anxiety level. There was no significant difference between pre- (M = 40.40, SD = 8.81) and post-task (M = 42.83, SD = 9.72, t(29) = -1.30, MSE = 0.76, n.s.) state anxiety levels. This result indicates that state anxiety was not provoked by this task. Size comparison task A 3 (facial pair: Happy-Angry, Angry-Neutral, NeutralHappy) 9 2 (surrounding circle size: large, small) repeated measures ANOVA was conducted to examine the effect of attention induced by facial expressions on size perception.
Psychological Research
A significant main effect for surrounding circle size was observed (F(1, 29) = 13.35, MSE = 130.58, p \ 0.01, g2p = 0.28). This result indicates that the central target circle was perceived as large when the surrounding circles were small compared to the size perceived when the surrounding circles were large. A significant effect for facial pairing (F(1.65, 56.18) = 18.93, MSE = 209.66, p \ 0.01, g2p = 0.36) was also observed such that angry faces captured more attention than happy ones and neutral faces captured more attention than happy ones. The results showed a significant effect of interaction between the surrounding circles and facial stimulus (F(1.68, 57.22) = 4.01, MSE = 15.62, p \ 0.05, g2p = 0.11). This result indicates that the effect of facial expression on size perception varied by the size of the surrounding circles. For additional analysis, a paired t test was conducted to compare the differences in the pattern of size perception for each facial pair within each size condition (Fig. 2). The results were significant for the Happy–Angry pairs for small surrounding circles, t(34) = 2.84, MSE = 0.69, p \ 0.01, and large surrounding circles, t(34) = 4.97, MSE = 70, p \ 0.01; and for the Happy-Neutral pairs for small surrounding circles, t(34) = 2.75, MSE = 0.79, p = 0.01, and large surrounding circles, t(34) = 5.51, MSE = 0.65, p \ 0.01. These results indicate that participants perceived the angry faces as large in the Happy– Angry pairs and neutral faces as large in the Happy–Neutral pairs. These results also suggest that this pattern of size perception was similar for both size conditions. However, no significant result was observed for the Angry–Neutral pairs in either size condition, preventing us from identifying a difference in size perception for angry versus neutral faces.
Discussion The current study aimed to examine the effect of attention induced by facial expressions on size perception using a modified Ebbinghaus illusion as a measurement tool. The result suggests that the perception of the central target circle as large means that the size of the surrounding circles was perceived as small relative to the central target circle. This might indicate that the facial stimuli that were contained within the surrounding circles attracted little attention. In contrast, the perception of the central target circle as small might means that the surrounding circles were perceived as large relative to the central target circle. This might indicate that the facial stimuli that were contained within the surrounding circles attracted greater attention. In the current task, the central target circles were blank, and the surrounding circles contained facial expressions. Thus, the facial expressions to which the participants paid more attention could be identified by comparing the facial pairs presented on the two sides of the screen. The results from this study showed that the angry faces led to an overestimation of size relative to the happy faces in the Happy–Angry pairs. This result suggested that the angry faces attracted more attention than the happy faces, in agreement with previous studies that found that angry faces attract more attention than happy faces (Eastwood et al., 2003; Juth et al., 2005; Pinkham et al., 2010). This result indicated that individuals would be more susceptible to angry faces than happy faces. Interestingly, the results of the Neutral–Happy pairs revealed that participants perceived the neutral faces as larger than the happy faces, which indicates that the neutral faces attracted more attention than the happy faces. Additionally, there was no statistically significant
Fig. 2 Ratio of response differences for each facial pair in small and large conditions
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difference between the neutral faces and the angry faces in the Neutral–Angry pairs. One interpretation of these results is that participants perceived both neutral faces and angry faces as negative facial expressions. Therefore, both neutral and angry faces may attract more attention than happy faces. These results are consistent with previous studies that found that neutral faces may be evaluated negatively as angry faces depending on social norms or investigators’ expectations (Parrot & Hertel, 1999). Another purpose of this study was to examine attentional resource allocation with respect to size perception using the Ebbinghaus illusion that has been supported by a series of assumptions. To this end, size comparison tasks were performed with the facial expressions attracting attention. According to the New Look theory, happy and angry faces are perceived as larger than neutral faces. However, according to the principle that describes the effect of motivation on size perception, happy faces should be perceived as larger than angry or neutral faces. The results of the current study showed that both the angry and neutral faces were perceived as larger than the happy faces, in disagreement with both explanations. This result might indicate that negative stimuli attract more attention than positive stimuli, as has been reported in several studies (Eastwood et al., 2003; Juth et al., 2005; Pinkham et al., 2010). Therefore, negative stimuli may enhance attention to a greater extent than positive stimuli, leading to a larger perceived size of negative stimuli. The results of this study can explain some of the mechanisms underlying size perception. In this study, we used attention-inducing stimuli combined with attentiondistracting stimuli in the Ebbinghaus illusion task. We confirmed that emotion-related information can attract attention and alter size perception. Based on the importance of facial expressions in social interactions, the perception of an object’s size as large may be an adaptive strategy that can be easily implemented in a social environment (Veltkamp et al., 2008). Therefore, the fact that negative faces are perceived as larger than happy faces indicates that people are more affected by angry faces than happy faces, which may suggest a strategy for coping with negative feedback in social circumstances by focusing attention on negative stimuli (Cannon, 1929). This study also attempted to explain the allocation of attentional resources using the Ebbinghaus illusion as a measurement tool based on a series of assumptions. Although the size of the surrounding circles was modified from the original Ebbinghaus illusion and facial expressions were applied as the stimuli, the results replicated the visual illusion of the original Ebbinghaus illusion. When pairs of facial expressions were compared, the central target circle was perceived as larger in the small condition than in the large condition. This result indicates that the large condition is
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more appropriate when measuring attention to facial expressions with the Ebbinghaus illusion because it ensures that the stimuli will be clearly recognized. However, because similar patterns of size perception with facial expressions appeared in both size conditions, these results show that the visual illusion was maintained despite a modification of the shape of the Ebbinghaus illusion and the use of facial expressions as stimuli. These results also suggest that the Ebbinghaus illusion is an appropriate tool for measuring attention. Although we investigated the mechanism of size perception using attentional factors, there are some limitations to this study. First, our paradigm consisted of an indirect measurement of attention toward stimuli without measuring the real allocation of attention or cognitive processes. Therefore, further studies should consider a manipulation task that assesses attentional patterns of the stimuli using an eyetracker or other instrumentation. Second, we used only a few types of positive and negative facial expressions. Further studies should investigate not only the effect of other types of facial expressions on size perception but also the effect of other types of emotional stimuli on size perception. Lastly, only female participants were included in this experiment. Furthermore, only female faces were included as the task stimuli because responses to the facial emotions of the same and opposite gender may differ. Thus, further research is required to replicate the experiment using both male and female models as well as male and female participants. Despite these limitations, this study empirically examined the mechanisms of emotion-induced attention with respect to size perception. Through this paradigm of size perception, our results suggest which facial expressions allocate more attention within the context of social interactions. The development of a measure that can determine whether an individual is able to focus his or her attention on relevant stimuli and ignore irrelevant stimuli may be helpful in the treatment of individuals who have difficulty with social interactions.
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