volunteers to watch and listen to a series of 4-min film clips and self-report ..... was relayed to a separate Apple IIe computer and visually monitored dur-.
Motivation and Emotion, Vol. 17, No. 4, 1993
The Face of Interest 1 J o h n m a r s h a l l Reeve 2 University of Wisconsin at Milwaukee
The present paper explores the validity of 16 facial movements" (e.g., eyelid widening, lips part) and two psychophysiological responses (e.g., heart rate) as interest-associated behaviors. In a pilot study we selected interesting and uninteresting stimuli~ and in two experiments we asked undergraduate volunteers to watch and listen to a series of 4-min film clips and self-report their level of interest. As each participant viewed the films, we videotaped, coded, and scored his or her facial movements and recorded the autonomic responses. Using repeated-measure ANOVAs and correlational analyses, we found support for five upper facial behaviors (eyes closed, number of eye glances, duration of eye glances, eyelid widening, exposed eyeball surface), one lower facial behavior (lips part), and two general head movements (head turns, head stillness) as interest-associated facial movements. The discussion focuses on how these findings confirm, contradict, and clarify the observations of others ~.g., Darwin, Tomkins, Izard). . . . . . . .
Some emotions express themselves uniquely on the human face. During fear, for instance, the eyebrows raise and draw together, wrinkles appear across the center of the forehead, and the lips part, stretch, and draw back (Ekman & Friesen, 1975). Like fear, anger, joy, distress, surprise, and disgust also show unique facial characteristics (Ekman & Friesen, 1975; tI wish to extend my gratitude to the codirectors of the Center for Research on the Effects of Television (CRETV), Cyndy Schiebe of Ithaca College and John Condry of Cornell University, for allowing me use of videotapes from the CRETV archives that served as experimental stimuli in the present set of studies. I also extend my gratitude to associate editor Condry, Glen Nix, Ed Deci, and two anonymous reviewers for their insightful and constructive comments on an earlier version of the manuscript. 2Address all correspondence concerning this article to Johnmarshalt Reeve, Department of Educational Psychology, School of Education, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201. 353 0146-7239/93/1200~)353507.00/0 © 1993PlenumPublishingCorporation
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Ekman, Friesen, & Ellsworth, 1982). Some researchers now add contempt as a seventh emotion-associated facial expression (Ekman & Friesen, 1986, 1988; Izard & Hynes, 1988), because they find that faces displaying one particular facial movement (i.e., unilateral lip raise and tighten) yield high pan-cultural agreement that they are contempt-associated. In the present paper, we hoped to do for interest what others have done for contempt, namely identify precisely which facial behaviors are (and are not) associated with the experience of the emotion. Two decades ago, Izard (1971) proposed that interest has a unique, highly recognizable facial expression. Skeptics, however, pointed to methodological difficulties in Izard's early work and suggested that head position, rather than facial expression, was the dominant and recognized emotion movement in his photographs (e.g., Ekman & Oster, 1979). Today, few emotion researchers endorse the idea of an interest-associated facial expression. This contemporary opinion, however, stems more from the absence of empirical support than it does from any conviction to disconfirming evidence. Given this state of affairs, we presumed that emotion researchers may not yet know which specific facial movements actually portray the interest expression. For example, there is little evidence (beyond careful observation) about whether the interest expression features a tilted head, or widened eyes, or an open mouth. Consequently, the purpose of the present investigation was to explore the validity of a variety of facial behaviors as interest-associated movements. Though our efforts were largely exploratory, a review of the literature offered a number of hypotheses for interest-associated facial behavior. Tomkins (1962, 1980) contended that the eyebrows are lowered and the eyes fixed staringly on the objects of one's interest. Izard (1977) emphasized a wide opening of the eyelids as well as a raising (but sometimes lowering) of the eyebrows. In his studies with infants (Langsdorff, Izard, Rayias, & Hembree, 1983), Izard proposed that 2-, 4-, 6-, and 8-monthold faces show interest through one or more of the following: brows raised, brows knit, eyes widened and rounded, eyes squinted, cheeks raised, mouth opened and relaxed, tongue moved, and lips pursed. Izard also added that interest expresses itself through an increased muscle tone without observable movement. Hass (1970) agreed that interest is associated with inhibited movement, but he stressed only the face's, rather than the body's, immobility. For Hass, interest is almost wholly expressed through the direction of the eyes. Others have suggested that an opening of the mouth (or a relaxing of the jaw) occurs during interest, an oral movement that presumably facilitates attention, concentration, and information processing (via quieted breathing; Darwin, 1872; Haagh & Brunia,
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1984). Izard (1990) seemed implicitly to agree with an interest-associated opening of the mouth, as the lips are parted in 11 of the 12 photographed faces he used to illustrate the interest expression. More than any other set of facial movements, we felt that eye behavior would be associated with interest. Eye behavior, however, is difficult to c a p t u r e in still p h o t o g r a p h s , the m e t h o d o l o g y used in cross-cultural studies of facial expressions. It is difficult, for instance, to illustrate the (hypothesized) interest state--inhibition of blinking, slight eyelid widening, inhibition of lateral eye movements, rigid head position, etc.---with a stereotyped, fixed display (as one can do with the other emotions such as joy or anger). For this reason, we arranged for participants to experience varying levels of interest (by encountering interesting and uninteresting stimuli) while we videotaped their facial expressions over time. We took a number of a priori selected facial behaviors and tallied each's frequency of occurrence during episodes of high and low interest to see which behaviors, if any, would discriminate interested from uninterested episodes. To operationally define these facial behaviors, we started with Ekman and Friesen's (1978) Facial Action Coding System (FACS) and amended five additional facial behaviors we presumed related to interest. This combination made it possible to test for the validity of six upper facial behaviors (eye blinks, eyes closed, number of eye glances, duration of eye glances, pupil dilation, eyelid widening), five lower facial behaviors (lips part, jaw drop, yawns, lip wipes, and smiles), and four general movements (head turn, head tilt, shoulder tilt, and head stillness). In addition to testing for the validity of these 15 facial movements, we explored for possible interest-associated autonomic nervous system (ANS) responses as well. We tested for two ANS responses, heart rate (HR) and skin resistance (SR), because previous research suggested their association with the interest emotion. As to heart rate, one group of researchers found interest to covary with HR (to be consistent with) deceleration in infants (Langsdorff, Izard, Rayias, & Hemree, 1983). Further, Fowles (1983) found HR deceleration followed quietened somatic activity, one category of our hypothesized interest facial behaviors (i.e., head stillness). As to the second ANS response, skin resistance is responsive to the psychological significance of a stimulus (Bernstein, Taylor, & Weinstein, 1975), a likely prerequisite to interest activation, We also tested for SR because Berlyne (1966; Berlyne, Craw, Salapatek, & Lewis, 1963) repeatedly found that the skin conductance response occurred reliably following exposure to interest-generating stimulus patterns.
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EXPERIMENT 1 Method
Participants Twenty-six introductory psychology students (15 females and 11 males) participated in exchange for extra course credit.
Material Film Clips. To select stimuli to induce the experience of high or low interest, we explored the videotape archives of the Center for Research on the Effects of Television (CRETV), a television research laboratory that is the joint project between Cornell University and Ithaca College in Ithaca, New York. From the CRETV archives, we hand-picked 12 videotapes and edited each clown to a 4-min segment. We used these 12 edited videotapes for pilot testing to identify three types of films: one uninteresting, one moderately interesting, and one highly interesting. (We wished to employ the moderately interesting film only during a pre-data-collection baseline period of the experiment.) In the pilot study, we felt it absolutely necessary to find two experimental films that differed greatly in their capacity to elicit interest while not differing in their capacity to elicit other emotions that might covary with interest (e.g., joy, surprise, and fear). Thus, in the pilot study we obtained emotion ratings (using a short form of the Differential Emotions Scale, Izard, Dougherty, Bloxom, & Kotsch, 1974) from 15 undergraduates for each film. Several films were rated as interesting without activating the "negative emotions," but only one pair of videotapes differed in how interesting participants reported them to be while not differing in how enjoyable participants found them to be. We avoided selecting a film that was both interesting and enjoyable so we could nullify any potential confound that might occur if the highly interesting film was interesting partly because it was enjoyable (or humorous). The names and mean (possible range 0 to 10) interest (/) and enjoyment (E) ratings for the two films selected for inclusion in Experiment 1 were Today's" Business (I = 2.3, E = 1.7) and Big Blue (I = 9.0, E = 3.3). The moderately interesting film (for the baseline period) was Jacques Cousteau (I = 5.5, E = 4.1). Today's Business (uninteresting film) was a weekly television show with a news format in which a host and her guests discussed various (outdated) topics related to money and business, including the Dow Jones industrial average, investment advice, and commentary on U.S. protectionism
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of its international markets. Jacques Cousteau (moderately interesting film) was a pioneering journey by the renowned Cousteau group of undersea explorers down a river in Louisiana, Peru. Big Blue (interesting film) was a movie excerpt that featured a competitor's preparation and slow-motion approach to a diving platform and his somewhat suspenseful descent into the depths of the ocean. Measures of Facial Behavior. Two independent raters coded and scored 15 discrete facial behaviors. Ten facial behaviors were scored according to Ekman and Friesen's (t978) FACS: eye blinks, eyes closed, number of eye glances, lips part, jaw drop, mouth stretch, smiles, lip wipes, head turn, and head tilt. For the remaining five behaviors, we could not rely on a previously validated scoring technique (duration of eye glances, pupil size, eyelid widening, shoulder tilt, and head stillness). Of these 15 behaviors, six were upper facial behaviors, five were lower facial behaviors, and four were general head movements. The operational definitions and interrater reliability coefficient for each of the six upper facial behaviors were as follows: eye blinks (.94), upper and lower eyelids touching followed immediately by eyelids open; eyes closed (.74), upper and lower eyelids touching for (at least) one-half second followed by eyelids open; number of eye glances (.87), lateral eye movements either to the right or left of television monitor; duration of eye glances (.82), cumulative seconds of lateral eye movements; pupil size (.43), vertical diameter of pupil in millimeters; and eyelid widening (.80), vertical distance from center of upper eyelid to center of lower eyelid in millimeters. The operational definition and reliability for each of the five lower facial behaviors were as follows: lips part (.78), cumulative seconds of separated lips (about 2 ram) though jaw is not lowered; jaw drop (.74), cumulative seconds of separated tips with jaw lowered and relaxed; mouth stretch (.84), or "yawn," mouth is stretched wide open; lip wipes (.93), tongue protrudes and moistens one or both lips; and smiles (.97), a facial action unit involving the simultaneous movement of Ekman and Friesen's (1978) cheek raise and lip corner pull. For smiles, we scored only a relatively strong lip corner pull that pulled the cheeks upwards, bagged the skin below the eyes, and produced crow's feet wrinkles beyond the eye corners, following Ekman's (1985) advice. The operational definition and reliability for each of the four general head movements were as follows: head turns (.75), rotating head right or left at least 30 ° from forward; head tilt (.85), angling head position right or left at least 10° from vertical; shoulder tilt (.75), angling the shoulders right or left from horizontal by at least 10°; and head stillness (.80), the head's degree of movement from an initial stationary position. To measure head stillness, we played the participant's videotape in fast forward (2x) after placing the eraser end of a pencil on the participant's
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nose and rated (1 to 5 scale) the nose's average extent of departure from its starting point (1 = no movement; 5 = continual movement). Because the interrater reliability for pupil size was inadequately low, we felt that a report of the data relevant to this facial behavior was not justified. Thus, 14 facial behaviors had sufficiently high reliability (.74 to .97) to be included in the data analyses. Measures of Autonomic Responding. We recorded skin resistance and heart rate with a H R M Software system (Mehler, Miller, Antonucci, & Cochran, 1986) interfaced with separate Apple IIe computers. To monitor skin resistance, silver/silver cloride electrodes were attached to the fingertips of the middle two fingers of the participant's left hand, and adhesive collars held the electrodes firmly against the skin. To monitor heart rate, a photoreflective densitometer was clipped to the participant's left earlobe to detect changes in blood volume. The analogue output from each system was relayed to a separate Apple IIe computer and visually monitored during the experiment. An Apple interface card read the skin resistance and heart rate inputs twice per second, and these data were stored in the computer's memory as kilohms (for skin resistance) and beats per minute (for heart rate). The data we report for skin resistance and heart rate are therefore the average of each participant's 480 data points obtained during each 4-rain film. Postfilrn Questionnaire. A six-item questionnaire featured three items to assess interest and three items to assess enjoyment. The questions that measured interest (on 1- to 7-point Likert scales) were "How interesting is the film clip? .... To what extent does the film clip stimulate your curiosity?" and "To what extent does the film clip hold your attention?" The alpha coefficient for the three-item interest measure was .92.
Procedure We ran participants one at a time. Upon entering the laboratory, the participant sat in a comfortable chair in a windowless, basement room with constant lighting. After overviewing the upcoming procedure, the experimenter attached the autonomic recording equipment to the participant. The experimenter next focused a videocamera that was 3 ft from the participant's face and on a line between the participant and a large television monitor, which was 20 ft from the participant's chair. The videocamera was positioned underneath the participant's line of vision to the television monitor and recorded the participant's face and shoulders. The experimenter began the data collection by starting two videocamera recorders, one that ran continuously to record the participant's facial movements and the other
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that ran continuously to display the experimental films on the television monitor. The participant watched one of two videotapes, each of which featured three separate films that lasted 4 min each. Each videotape began with the moderately interesting (Jacques Cousteau) film and then showed a counterbalanced order of the two experimental films. We used the moderately interesting film to introduce and familiarize the participant to the experimental procedure and to ensure that the ANS measures had stabilized. We did not use the data collected during the baseline period. After each film, the videotape included a 2-min rest period (i.e., a blank screen with no noise). Each videotape therefore played for 18 min (three 4-rain films and three 2-rain rest periods). At the beginning of the second and third rest periods, the experimenter asked the participant to complete the brief postfilm questionnaire (to assess interest). Throughout the film viewing, the experimenter remained behind the computer monitors, which were placed side-by-side and in such a way as to shield visual contact between experimenter and participant. At the conclusion of the film-viewing, the experimenter debriefed the participant and asked if he or she had seen any of the films before. In line with our pilot testing of the film clips, no participant reported having seen either the Big Blue or the Today's Business film, though one participant reported having seen the Jacques Cousteau film.
Results
We performed a separate one-way repeated-measures analysis of variance (ANOVA) for each dependent measure. To organize our report of the results, we first present the self-report interest ratings, second report analyses of the facial behaviors, and last report analyses of the autonomic NS responses. Following the repeated-measure ANOVAs, we report correlational analyses between the interest ratings and the facial and autonomic NS responses.
Effects of Type of Film on Interest Rating,~, Facial Behaviors, and Autonomic Responses Interest Ratings. Participants reported greater interest during the viewing of the interesting film (M = 5.73) than during the viewing of the uninteresting film (M = 2,95), The type of film main effect was significant, F(1, 25) = 44.92, p < .01.
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Table I, Means and Standard Deviations (in Parentheses) for Facial Behaviors and Autonomic Responses by Type of Filma Type of film Dependent measure Upper facial behaviors Eye blinksb Eyes closedb Number of glancesb Duration of glancesc Eyelid Widening (ram) Lower facial behaviors Lips part c Jaw drop c Yawnsb Smilesb Lip Wipesb General head movements Head turn c Head tiltc Shoulder tiltc Head stillnessa Autonomic responses Skin resistance (kohms) Heart rate (bpm)
Uninteresting
Interesting
3.694 (1.01) 0.41a (0.52) 1.04a (0.62) 1.644 (1.18)
3.14b (0.95) 0.t7b (0.30) 0,43b (0.40) 0.63b (0,61)
9.474 (2.09)
10.10b (2.04)
1.094 (1.73) 0.28a (0.73) 0.064
1.63a (2.23) 0.52a (1.54) 0.024
O.16)
(o.o8)
O.08a
O.02a
(o. 18)
(o.o8)
0.484 ({).42)
0.374 (0.44)
0.60,~ (0.86)
0.16b (0.36)
3.074 (2.79) 1.34a (2.75)
2.444 (2.94) 0.98a (2.43)
2.314 (1.19)
1.62b (0.94)
-2.054 (2.03)
-2.603, (2.12)
-3.22a (7.47)
-5.58a (4.89)
aAll group means are square root transformations of the actual means, except those for eyelid widening and head stillness. Means not sharing the same subscript are significantly different from one another, p < .05, n = 26 for each group. bFrequency per minute. CDuration of seconds per minute Ctl- to 5-point Likert scale; lower numbers reflect greater stillness.
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Facial Behaviors. The distributions for 12 of the 14 facial movements were positively skewed (all except eyelid widening and head stillness), so the scores for each of these 12 facial movements were subjected to a square root transformation. Table I shows the posttransformation means and standard deviations of each facial movement by type of film. For all five upper facial behaviors, the type of film effect was significant. For eyelid widening, there was a significant effect, F(1, 25) = 11.41, p < .01, such that eyelid widening was greater during the interesting film. The other four upper facial behaviors showed a similar pattern of results in which its frequency or duration was significantly less during the viewing of the interesting film: eye blinks, F(1, 25) = 27.95, p < .01; eyes closed, F(1, 25) = 9.00, p < .01; number of eye glances, F(1, 25) = 34.83, p < .01; and duration of eye glances, F(1, 25) = 30.71, p < .01. No lower facial behavior showed a significant main effect across type of film: lips part, F(1, 25) = 2.69, n.s.; jaw drop, F(1, 25) = 0.49, n.s., yawns, F(1, 25) = 1.30, n.s., smiles, F(1, 25) = 2.26, n.s.; and lip wipes, F(1, 25) = 3.40, p < .08. Two of the four general head movements showed a significant type of film effect: head turn, F(1, 25) = 6.80, p < .02, and head stillness, F(1, 25) = 14.46, p < .01, indicating that head turns were less frequent and the head was held more stationary during the viewing of the interesting film. Film type did not have a significant effect on either head tilt, F(1, 25) = 1.73, n.s., or shoulder tilt, F(1, 25) = 1.79, n.s. Autonomic Responses. We calculated SR and H R scores from change scores in which each participant's SR and H R during each film was subtracted from his or her SR and H R during the immediately preceding baseline rest p e r i o d . ( T h e d i s t r i b u t i o n s of SR and H R c h a n g e scores approximated the normal.) Table I shows the mean SR and H R change scores by type of film. Type of film failed to have a significant effect on either autonomic response: skin resistance, F(1, 25) = 2.55, n.s.; heart rate, F(1, 25) = 1.20, n.s. Exploratory data analyses showed that heart rate did, as expected, significantly decrease from baseline during the viewing of the interesting film, z = 5.82, p < .01; but heart rate also, unexpectedly, decreased significantly from baseline during the viewing of the uninteresting film, z = 2.20, p < .05. Correlational Analyses between Interest Ratings and Facial and Autonomic Responses The results presented thus far suggest that differences in facial movements emerged during the viewing of the two films. The next issue to consider is whether those differences correlated with self-reported interest
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ratings. To test for the bivariate association between the interest ratings on the one hand and the facial and autonomic responses on the other, we used zero-order correlations. For the five upper facial behaviors, three correlations were significant: eyes closed, r(52) = -.35, p < .05, two-tailed; number of eye glances, r = -.62, p < .01; and duration of eye glances, r = -.53, p < .01. Eye blinks showed a suggestive relationship with self-reported interest, r = -.25, p < .10. Eyelid widening did not correlated significantly with reported interest, r = .16. Only one lower facial behavior correlated significantly with interest ratings: smiles, r = -.29, p < .05, indicating that felt interest covaried with smile inhibition. The remaining four lower facial behaviors were not significantly correlated with self-reported interest: lips part, r = .17, n.s.; jaw drop, r = .17, n.s.; yawns, r = -.06, n.s.; and lip wipes, r = .07, n.s. For the general head movements, two correlations were significant: head turns, r = -.27, p < .05, and head stillness, r = -.30, p < .05. Neither head tilt, r = -.12, n.s., nor shoulder tilt, r = .08, n.s., correlated significantly with self-reported interest, Last, neither autonomic responding measure correlated significantly with interest ratings: skin resistance, r = -.05, n.s., and heart rate, r = -.18, n.s.
Discussion
The findings from Experiment t provide some support for the proposition that individuals display characteristic facial movements during the experience of interest versus disinterest. Each of the following facial movements discriminated between episodes in which the participants viewed the relatively interesting versus uninteresting film: eye blinks, eyes closed, number of eye glances, duration of eye glances, eyelid widening, head turns, and head stillness. Further, in the correlational analyses, eyes closed, number of eye glances, duration of eye glances, smiles, head turns, and head stillness correlated with subjective interest ratings. Before accepting the contention that level of interest is the causal variable underlying these differences in facial behavior, we considered one possible alternative explanation, namely that enjoyment, rather than interest, caused these facial differences. The type of film manipulation did have a significant effect on participants' enjoyment ratings (p < .01), an effect we anticipated because (1) the phenomenological experience of interest is to some extent an enjoyable one and (2) our past work (Reeve, 1989) showed interest and enjoyment ratings to correlate rather strongly with one another (r --- .70, p < .01, in the present data). In our effort to rule out this alternative interpretation, we intentionally included two facial move-
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ments we knew from our previous research (Reeve, 1991) to be highly related to enjoyment but not to interest: smiles and lip wipes. Looking at the results for smiles and lip wipes in Table I, there is no evidence that participants smiled and lip wiped more frequently during the interesting film. In fact, there was a trend for participants to smile and lip wipe more while viewing the uninteresting film, though both behaviors occurred infrequently. These two counterexamples suggest to us that interest, not enjoyment, best explains the differences in facial behaviors during the viewing of our experimental films.
EXPERIMENT 2 We conducted Experiment 2 to replicate and extend our findings from Experiment 1. In Experiment 1, we relied on a combination of Berlynian collative properties (i.e., complexity) and an element of suspense (after Zillman, 1980) to identify interesting versus uninteresting stimulus films. The extent to which a stimulus is complex or suspenseful is, however, only one way to activate interest. Interest also stems from the novelty of the stimulus material (e.g., Berlyne, 1966). Just as a complex or suspenseful stimulus is more interesting than simple or predictable stimulus, a novel stimulus is more interesting than a redundant one. Stimulus novelty is an especially important interest determinant because even a complex, suspenseful stimulus loses its interestingness quickly if it is repeated. Berlyne's consistent finding was that attention, curiosity, and exploratory behavior were highest upon a first stimulus encounter but each interest indicator declined markedly with a repeated presentation of that same stimulus (Berlyne, 1966; Berlyne, et al., 1963). Given that attention, curiosity, and exploratory behavior decline markedly following initial stimulus exposure, we suspected that a person's interest-associated movements would similarly decline from a first exposure to an interesting film and all subsequent exposures to that same film. Consequently, we designed Experiment 2 so that half of the participants watched the same interesting film (Big Blue) three consecutive times. The other half of the participants watched a series of three uninteresting, but different, films. This design allowed us to predict an interaction in which each interest facial behavior (e.g., eyelid widening) would be low but constant during the three viewings of the uninteresting/novel films, while the same facial behavior would be relatively high during the first viewing of the interesting film but progressively diminished during the film's repeated exposures. By way of illustration, we predicted that the pattern of eyelid widening during the three uninteresting films would be about 9.0 mm, 9.0 ram, and 9.0 mm, while the pattern of eyelid widening during the repeated
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interesting film would be about 10.5 mm, 9.0 mm, and 7.5 mm. Therefore, we predicted a significant type of Film x Number of Exposures interaction for each hypothesized interest facial movement. This experimental design also afforded us the opportunity to test for differences between facial movements associated with (dis)interest and facial movements associated with fatigue. We developed a special interest in possible fatigue-associated movements (that do not necessarily reflect disinterest) because we were puzzled by the lack of correspondence between several facial movements and reports of (dis)interest in Experiment 1. Specifically, we speculated that if yawns, jaw drop, head tilt, and shoulder tilt did not expresses (dis)interest, then perhaps they express fatigue, or tiredness. Therefore, we looked for these facial behaviors to show only a significant exposure effect (without a significant film by exposure interaction) for confirmation that they are fatigue-associated rather than disinterest-associated movements. Method
Participants Thirty-six introductory psychology students (19 females and 17 males) participated in exchange for extra course credit.
Materials Film Clips. For the repeated showing of an interesting film, we showed participants the same Big Blue film used in Experiment 1 three consecutive times. For the showing of the series of uninteresting but novel films, we showed participants the Today's Business film from Experiment 1 on exposure 1 but two different Today's Business films on exposures 2 and 3. Both of these additional Today's Business films were 4 min in length and equally uninteresting. The content of these films was as follows: Today's Business #2 discussed the government's liquidation of railroad company Conrail, the merger of two major oil companies, and a discussion of inflation and its causes; Today's Business #3 discussed a Senate committee's decision on a trade bill, U.S. foreign trade relations, and an interview with a "grey marketer" of computer chips. Measures of Facial Behavior. We used the same 14 facial behaviors from Experiment 13 and added one more, "exposed eyeball surface area." 3Because of our inability to measure it reliably, we did not include pupil dilation.
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We quantified exposed eyeball surface area by actually rating a proxy for amount of visible eyeball surface area, the percent exposure of the iris' outermost outline, or boundary, that was clearly visible to our raters, as suggested by Tsubota and Nakamori (1993). One rater independently coded and scored all the videotapes for each participant. A second rater independently coded a random sample of 32 of the 4-min videotape segments so that interrater reliability coefficients could be calculated and estimated. The interrater reliability coefficients for the 15 facial behaviors were as follows: eye blinks, .93; eye closed, .95; number of eye glances, .89; duration of eye glances, .95; eyelid widening, .70; lips part, .74; jaw drop, .97; yawns, .91; lip wipes, .84; smiles, .97; head turns, .78; head tilt, .77; shoulder tilt, .98; head stillness, .73; and exposed eyeball surface, .87. Postfilm Questionnaire. In Experiment 2 we added two questions to the postfilm questionnaire from Experiment 1 to assess stimulus novelty: "How novel is the film clip in its appearance?" and "How surprised do you feel while viewing the film clips?" Because these two items were positively and significantly correlated, r = ,56 (p < .01), we averaged them into a single measure. We repeated the same three questions from Experiment 1 to assess interest (individual items for interest, curiosity, and attention), and the three-item scale again had high internal consistency, alpha = .92.
Pivcedure The experimental procedure in Experiment 2 closely paralleled that from Experiment 1. We ran participants one at a time. The participant sat in a comfortable chair in a windowless, basement room with constant lighting, and the experimenter, after informing the participant of the experimental procedures, attached the autonomic recording equipment to the participant. Half of the participants watched the same Big Blue film three consecutive times, while the other half watched the series of three different Today's Business films. Both film sequences began with the 4-min moderately interesting (Jacques Cousteau) film and featured the three 4-min films with 2-rain between-films rest periods. Thus, all participants watched a 24rain videotape (four 4-min films with four 2-min rest periods) and completed the postfilm questionnaire three times (at the beginning of the second, third, and fourth rest periods). Results
We performed a separate mixed-design ANOVA for each dependent measure. In each analysis, type of film (interesting vs. uninteresting) was
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the between-groups factor and number of film exposures was the repeated, within-groups factor.
Effects of Type of Film and Exposure Number on Interest Ratings, Facial Behaviors, and Autonomic Responses Self-Report Ratings. The postfilm questionnaire assessed subjective interest and novelty. We collected novelty ratings as a manipulation check to determine whether participants rated the interesting film as less novel with each successive exposure. For the novelty ratings, there was a significant exposure effect, F(2, 68) = 9.39, p < .01, as well as a significant Film x Exposure interaction, F(2, 68) = 22.63, p < .01. Tukey post hoc tests showed that the mean novelty ratings to the series of uninteresting films did not differ across the exposure (Means, in order of exposure: 2.00 = 2.31 = 2.51), whereas the mean novelty ratings for the repeated interesting film decreased with each subsequent exposure (Means: 4.37 > 3.32 > 2.08). For the interest ratings, there was a significant exposure main effect, F(2, 68) = 10.40, p < .01, as well as significant Film x Exposure interaction, F(2, 68) = 22.28, p < .01. As with the novelty ratings, Tukeypost hoc tests showed that the mean interest ratings did not differ significantly from one another across the series of uninteresting films (Means: 2.65 = 3.11 = 3.07), while the mean interest ratings for the repeated interesting film decreased with each subsequent exposure (Means: 5.07 > 4.09 > 2.93). Facial Behaviors. As in Experiment 1, the distributions for 12 facial behaviors (all except eyelid widening, head stillness, and exposed eyeball surface) were positively skewed, so each of these 12 facial behaviors were subjected to a square root transformation. 4 Table II shows the means and standard deviations for all 15 facial behaviors by type of film and exposure number. Four upper facial behaviors showed a significant Film x Exposure interaction: number of eye glances, duration of eye glances, eyelid widening, and exposed eyeball surface. For number of eye glances, both the exposure, F(2, 60) = 28.21, p < .01, and the Film x Exposure interaction, F(2, 60) = 13.42, p < .01, effects were significant. For duration of eye glances, both the exposure, F(2, 60) = 23.53, p < .01, and the Film x Exposure interaction, F(2, 60) = 15.26, p < .01, effects were significant. For eyelid widening, both the exposure, F(2, 60) = 21.82, p < .01, and the Film x Exposure interaction, F(2, 60) = 5.50, p < .01, effects were significant. For 4We accidently taped over one videotape containing data for four participants, one male and one female in each condition. We report facial expression data for only 32 of the 36 participants.
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Table II. Means and Standard Deviations (in Parentheses) for Facial Behaviors and Autonomic Responses by Type of Film and Exposure Number a Dependent measure; type of film Upper facial behaviors Eye blinksb Uninteresting Interesting Eyes closedb Uninteresting Interesting Number of eye glancesa Unhlteresting Interesting Duration of eye glancesc Uninteresting Interesting Eyelid widening (ram) Uninteresting Interesting Exposed eyeball surface (% visible) Uniteresting Interesting Lower facial behaviors Lips p a r ( Uninteresting Interesting Jaw drop c Uninteresting
Exposure number First
Second
Third
4.734 (1.24)
4.86,~ (t.16)
4,71a (1.16)
3,62b (1.38)
3.67b (1,61)
3,81b (1.75)
0.494b (0.50)
0,70ab (0.36)
0.764 (0,71)
0,32b (0.43)
0.51,~b (0.49)
0,65ab (0.62)
0.844b (0.61)
0.88b (0.58)
0.95t, (0.48)
0.56.~ (0.53)
0.98b (0.60)
1.45c (0.68)
1.21 at, (1.11)
1.264b (0.92)
1.344b (0,87)
0.78a (0,74)
1.54b (1.07)
2.50c (1,48)
9.024 (2.03)
8.9 la (1.78)
8.474 (1.67)
11.47b (2.02)
10.58c (1.72)
9.99c (1.85)
62.9ab (5.8)
61.74 (6.5)
60An (6.4)
68.2c (4.9)
64.6b (4.9)
61,04 (5.3)
1.284b (2A6)
1.40ab (2.05)
1.274b (2.33)
t .964 (2.28)
0.6% (1.18)
0,8% (1.18)
0.434 (0.77)
0.354 (0.51)
0.50,~ (0,89)
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Table II. Continued Dependent measure; type of film Interesting Yawnsb Uninteresting Interesting Smilesb Uninteresting Interesting Lip wipesb Uninteresting Interesting
Exposure number First
Second
Third
0.5ta (0.66)
0.434 (0.59)
0.534 (0.50)
0,09ab (0.25)
(0.31)
0.20ab (0.37)
0.064 (0.17)
0.0G (0.00)
0.32b (0.50)
O.OOa (0.00)
O.03ab (0.13)
0,0G (0.00)
O.05ab (0.21)
O.lOab (0.31)
0,18b (0.30)
0.444 (0.41)
0.404 (0.37)
0.39a (0.46)
0.504 (O.4O)
0.3% (0.45)
0,43a (0.36)
0.404
(0.70)
0.404 (0,72)
0.36a (0.49)
0.05b (0.21)
0.484b (0.70)
0.95b (0.92)
1.124 (1.44)
1,9lab (2.20)
2.97bc (2.66)
2.50abe (2.44)
3.95c (2,49)
3,96c (1.71)
0.974b (2.39)
1.364b (1.84)
2.454 (3.60)
0.06b (0.24)
0.544b (1.84)
1.624b (2,41)
1.874 (0.92)
2.40bc (1.18)
2.40bc (1.06)
2.06ab (1.09)
2.65c (1,06)
(1.oo)
O.18ab
General head movements Head turn c Uninteresting Interesting Head tiltc Uninteresting Interesting Shoulder tiltc Uninteresting Interesting Head stillnessd Uninteresting Interesting
3.354
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369
"Fable I1. Continued Dependent measure; type of film Autonomic responses Skin Resistance (kohms) Uninteresting Interesting Heart rate (bpm) Uninteresting Interesting
Exposure number First
Second
Third
-0.384b (1,68)
-1.24ac (1.74)
-1.48c (1.55)
--0.24b (0.93)
--1.46c (1.69)
-1.34c (0.83)
-3.254 (4.93)
-2.79,~ (3.18)
-3.234 (4.21)
-4.104 (6.47)
-2.2% (4.19)
-0.624 (5.67)
aAll group means, except those for eyelid widening, retinal circumference, and head stillness, are square root transformation of the actual group means. Means not sharing the same subscript are significantly different from one another, p < .05. For each facial behavior, n = 16; for each autonomic response, n = 18. bFrequency per minute. CDuration of seconds per minute. all- to 5-point Likert scale; higher numbers reflect greater stillness.
exposed eyeball surface, both the exposure, F(2, 60) = 35.84, p < .0l, and the Film x Exposure interaction, F(2, 60) = 7.32, p < .01, effects were significant. One upper facial behavior, eyes closed, showed only a significant exposure main effect, F(2, 60) = 5.18, p < .01, while the Film x Exposure interaction was not significant, F(2, 60) = 0.05, n.s. The final upper facial behavior, eye blinks, showed neither an exposure, F(2, 60) = 0.41, n.s., nor a Film x Exposure interaction, F(2, 60) = 0.90, n.s., effect. Of the five lower facial behaviors, only one showed a significant Film × Exposure interaction. For lips part, the Film x Exposure interaction was significant, F(2, 60) = 3.93, p < .03, while the exposure main effect approached significance, F(2, 60) = 3.06, p < .06. For yawns the exposure effect was significant, F(2, 60) = 4.58, p < .02, while the Film x Exposure interaction was not, F(2, 60) = 2.32, n.s. The remaining three lower facial behaviors showed neither an exposure main effect nor a Film x Exposure interaction effect: jaw drop, exposure, F(2, 60) = 0.73, n.s., Film x Exposure interaction, F(2, 60) = 0.05, n.s.; smiles, exposure, F(2, 60) = 1.29, n.s., Film x Exposure interaction, F(2, 60) = 1.48, n.s.; and lip wipes, exposure, F(2, 60) = 0.85, n.s., Film x Exposure interaction, F(2, 60) = .0.60, n.s.
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Two general head movements showed a significant Film x Exposure interaction effect. For head turns, both the exposure, F(2, 60) = 6.98, p < .01, and the Film x Exposure interaction, F(2, 60) = 8.31,p < .01, effects were significant. For head stillness, both the exposure, F(2, 60) = 26.12, p < .01, and the Film x Exposure interaction, F(2, 60) = 5.54, p < .01, effects were significant. The other two general head movements showed only a significant exposure main effect: head tilt, exposure, F(2, 60) = 7.90, p < .01, Film x Exposure interaction, F(2, 60) = 0.78, n.s.; shoulder tilt, exposure, F(2, 60) = 5.18, p < .01, Film x Exposure interaction, F(2, 60) = 0.01, n.s. Autonomic Responding. As in Experiment 1, we calculated skin resistance and heart rate scores from change scores in which each participant's SR and H R during each film was subtracted from his or her SR and H R during the immediately preceding baseline period. Table II shows the mean SR and H R change scores by type of film and exposure number. For skin resistance, only the exposure main effect was significant: exposure, F(2, 68) = 16.41, p < .01; Film x Exposure interaction F(2, 68) = 0.47, n.s. For heart rate, neither the exposure, F(2, 68) = 1.24, n.s., nor the Film x Exposure interaction, F(2, 68) = 1.19, n.s., effects were significant. Exploratory data analyses, however, showed that H R did decrease significantly from baseline during the first exposure to the interesting film, z = 2.69, p < .01, while it did not do so during the third exposure, z = 0.47.
Correlational Analyses As in Experiment 1, we used (zero-order) correlational analyses to examine the bivariate relationships between interest ratings and each of the facial behaviors and autonomic responses. In the correlational analyses, we used each participant's data relevant to the first film exposure only. We did not use data from the two subsequent exposures to avoid violating the assumption of nonindependence of residuals (Tabachnick & Fidell, 1989): variance of the interest ratings was much greater on film exposure 1 than on subsequent exposures; and the distribution of interest ratings on exposure 1 was normal while it was significantly positively skewed by exposure 3. Among the six upper facial behaviors, three correlations were significant: eyes closed, r(32) = -.34, p < .05, one-tailed; number of eye glances, r = -.32, p < .05; and duration of eye glances, r = -.33, p < .05. Three upper facial behaviors did not correlate significantly with interest: eye blinks, r = -.26, n.s., eyelid widening, r = .19, n.s., and exposed eyeball surface, r = .25, n.s. Among the five lower facial behaviors, two correlations
Interest
371
w e r e significant: lips part, r = .35, p < .05, and yawns, r = -.32, p < .05. T h r e e lower facial behaviors did not correlate significantly with interest: jaw drop, r = -.09, n.s.; smiles, r = -.16, n.s.; and lip wipes, r = .03, n.s. A m o n g the four general h e a d m o v e m e n t s , two c o r r e l a t e d significantly with interest: h e a d turns, r = -.33, p < .05, and head tilt, r = .36, p < .05. T w o g e n e r a l m o v e m e n t s did not correlate significantly with interest: s h o u l d e r tilt, r = -.12, n.s., and h e a d stillness, r = -.22, n.so Last, n e i t h e r a u t o n o m i c r e s p o n d i n g m e a s u r e correlated significantly with self-reported interest: skin resistance, r = -.t0, n.s., and h e a r t rate, r = -.06, n.s.
GENERAL DISCUSSION In E x p e r i m e n t 1 participants watched and listened to stimuli that differed in their capacity to activate interest, and we found that participants displayed m a r k e d l y different facial m o v e m e n t s during the two stimulus exposures. In E x p e r i m e n t 2 participants w a t c h e d and listened to the s a m e interesting stimulus on three consecutive occasions, and we found that participants' facial m o v e m e n t s c h a n g e d predictably as the otherwise interesting stimulus lost its novelty. Eight facial m o v e m e n t s differed in a c c o r d a n c e with o u r m a n i p u l a t i o n s of interesting versus uninteresting stimuli: n u m b e r of eye glances, d u r a t i o n of eye glances, eyes closed, 5 head turns, eyelid widening, exposed eyeball surface, lips part, and head stillness. F o r five of these facial m o v e m e n t s ( n u m b e r o f eye glances, d u r a t i o n of eye glances, eyes closed, h e a d turns, and head stillness) the results were robust across b o t h experiments, using b o t h r e p e a t e d m e a s u r e s and c o r r e l a t i o n a l analyses. Eyelid widening was sensitive to the two film manipulations, but it did not correlate (significantly) with subjective interest. 6 Lips part was sensitive only to o u r m a n i p u l a t i o n of novelty. E x p o s e d eyeball surface was included only in E x p e r i m e n t 2, but it was sensitive b o t h to how interesting the film was on its first exposure as well as to h o w interesting the film was across r e p e a t e d Sin retrospect, the finding that eyes closed did not show a Film x Exposure interaction effect in Experiment 2 was not surprising. As the interesting film was repeated, participants became increasingly likely to glance their eyes away from the television monitor (see Table II). When participants glanced away from the repeated film, they did not make eye closures (because they were looking at relatively novel objects in the room). When participants actually looked at the monotonous film, they did, however, show an increase in eyes closed. Our findings suggest that disinterested participants choose either to close their eyes, glance their eyes away, or turn their head away, sometimes preferring one motoric pattern of attentional shift over another. 6Perhaps, participants widen their eyes without having this facial behavior feed back and contribute to a conscious experience of interest, or perhaps eyelid widening facilitates attentional processes that are not necessarily mobilized by the interest emotion (though this seems harder to imagine).
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exposures; it did not, however, correlate significantly with subjective interest. At the beginning of our investigation we expected an additional cluster of facial movements---yawns, jaw drop, head tilt, and shoulder tilt--to correspond to level of interest as well, but we found little experimental evidence that any of these behaviors was interest-associated. Rather, we found yawns, head tilt, and shoulder tilt to be associated with fatigue, or tiredness, as each behavior showed a significant exposure main effect without showing a significant Film x Exposure interaction effect in Experiment 2. Further, we included smiles and lip wipes to function as counterexamples against the idea that enjoyment (rather than interest) explained the differences in facial movements during the viewing of our experimental films. In neither experiment did either smiles or lip wipes vary in accordance with our manipulation designed to effect how interesting the stimuli were to participants. Taken as a whole, our list of validated interest-associated facial movements confirm, contradict, and clarify the insightful observations of Tomkins, Izard, Hass, Darwin, and others. As to confirmation, our findings stand out as strong confirmation of the so-called "hard stare" in which a person's eyes are fixed on the object of interest, as our interested viewers' made few lateral eye movements (eye glances), widened their eyelids, exposed more of their eyeball, infrequently closed their eyes, made fewer lateral head turns, and stilled their head movement. As to contradiction, we found no evidence to support the contention that the eyebrows are lowered (or raised) during interest. Our raters found the movements of the eyebrows to be fully uninformative. It remains a possibility, however, that future studies that choose to focus on the surface electromyographic (EMG) activity of otherwise unobservable eyebrow movements (e.g., Cacioppo, Petty, Losch, & Kim, 1986) might show that subtle eyebrow movements do covary with interest experiences, but such studies remain to be completed (but see Cohen, Davidson, Senulis, Saron, & Weisman, 1991). Further, we found little support for Langsdorff et al. 's (1983) proposition that brows knit, eyes squinted, cheeks raised, tongue moved, and lips pursed are interest-associated facial movements. The most likely explanation for the discrepancy between Langsdorff et al.'s proposed set of interest indicators and our findings is that Langsdorff et al.'s participants were infants, whose facial movements are involuntary responses, while our participants were college-aged adults, whose facial movements are voluntary as well as involuntary (e.g., Rinn, 1984). Finally, as to clarification, our findings help pin-point more precisely the action of the mouth, lips, and jaw during interest. We found that the mouth was opened only slightly and that the lower jaw was not relaxed during interest; rather, the lips parted slightly
Interest
373
(about 2 mm) with a slight raising of the upper lip and slight lowering of the lower lip. Our findings also support Tomkins' (1962) contention that interest is somewhat unique among the (major) emotions, because of its gradual onset and decline. Tomkins based his statement on the different rates of electrocortical activity that emotions show immediately prior to their activation. Surprise, fear, and interest, for instance, are each activated by an increase in the rate of neural firing, but surprise and fear activation involve relatively sudden electrocortical activity increase, whereas interest activation involves a relatively gradual increase. Our findings suggest that one must monitor facial behavior for several seconds before many of the interest-associated facial movements begin to provide the data necessary to discriminate interested from disinterested faces. Thus, while a still photograph of a "surprise expression" clearly communicates a person's emotional state, a reliance on a static "interest facial expression" wilt be less informative. To portray the full face of interest, it seems necessary to supplement the movements of eyelid widening, eyeball exposure, and lips part (which can be portrayed in a still photograph) with an over-time display of head stillness, an absence of eye glances, an absence of head turns, etc. (which can best be portrayed in a multiple-second videotape). That notwithstanding, it remains a testable hypothesis whether or not eyelid widening, exposed eyeball area, and lips part can reliably and effectively communicate interest in a still photograph. There are two significant limitations that need to be made explicit in our studies that work together to encourage a conservative interpretation of our findings. First, our data do not allow us to generalize beyond the visual and auditory stimuli of our film clips to include nonvisual, nonauditory stimuli such as olfactory stimuli or mental images. Further, it is not at all clear whether or not interesting versus uninteresting auditory stimuli would produce the same pattern of results as found in the present set of experiments. Essentially, this is a debate as to whether the present study focused on "interest" or on "visual interest." This is a particularly important limitation on the present findings because so many of the validated facial behaviors were eyes-related movements. It remains to be demonstrated whether people will widen their eyes, expose their eyeballs, inhibit their lateral eye movements, etc., during exposures to interesting nonvisual stimuli. Second, our data do not speak to the question of whether our validated interest-associated facial movements "hang together" in a coherent facial expression. It is not clear, for instance, whether interested persons widen their eyes and part their lips or widen their eyes or part their lips. What our data do show, however, is that several facial behaviors occur more or less frequently in accordance with interest and these interest-as-
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s o c i a t e d b e h a v i o r s t o s o m e e x t e n t c o n f i r m , to s o m e e x t e n t c o n t r a d i c t , a n d to a n o t h e r e x t e n t clarify t h e a f o r e m e n t i o n e d o b s e r v a t i o n s o f o t h e r s .
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