Running head: HUMOR, TICKLE, AND PAIN Facial Expressions, Smile Types, and Self-report during Humor, Tickle, and Pain: An Examination of Socrates’ Hypothesis

The nature of ticklish smiling and the possible emotional state that accompanies it have been pondered since the ancient Greeks. Socrates proposed that tickle induced pleasure and pain. Others, including Darwin, have claimed that ticklish laughter is virtually the same as humorous laughter. The present study is the first to systematically examine facial behavior and self-reports of emotion in response to tickling. Using a within-subjects design, 84 subjects’ responses to being tickled were compared to their responses when experiencing a painful stimulus and their responses to comedy. Overall results for both self-report and facial action coding showed that the tickle condition elicited both pleasure and displeasure. Facial action during tickling included “Duchenne” smiles plus movements associated with negative emotions. Results suggest that tickle-induced smiling can be dissociated from positive affect. Tickle may be a type of complex reflex or fixed-action pattern. Facial Expressions 4 Facial Expressions, Smile Types, and Self-report during Humor, Tickle, and Pain: An Examination of Socrates’ Hypothesis Tickling and the smiling it induces, at first blush, seem like child’s play. However, tickle, along with crying and startle responses, falls into the category of poorly understood affective phenomena. One intriguing aspect of tickle is that a physical stimulus can elicit a response that appears to closely resemble that of humor. The apparent similarity of the smiling and laughter induced by tickle and by humor has led many writers to assume that the two reflect the same internal state. One champion of this view was Charles Darwin (1872), who noted that “the imagination is sometimes said to be tickled by a ludicrous idea; and this so-called tickling of the mind is curiously analogous with that of the body” (p.199). Darwin described several similarities between tickle and humor. First, he claimed that a pleasant hedonic state was necessary to elicit laughter: “in this case, [humor] and in that of laughter from being tickled, the mind must be in a pleasurable condition; a young child, if tickled by a strange man, would scream in fear” (p.199). Second, he noted similarities in the elicitor of both states, “The touch must be light” in tickle and “an idea or event must not be of grave import” in humor. Finally, he pointed out that an element of surprise is required to elicit laughter to jokes or to tickle. In essence, tickle was simply a physical joke. Much contemporary writing on the topic echoes the view that ticklish laughter and smiling is the result of a positive affective state (e.g. Keith-Spiegel, 1972; Panksepp, 2000; Weisfeld, 1993). In contrast, Francis Bacon (1677) proposed that when tickled “men even in a grieved state of mind, yet cannot sometimes forbear laughing” (p. 151). This view suggests that ticklish smiling and laughter can be dissociated from a humorous state. Moreover, Bacon suggested that “tickling is ever Facial Expressions 5 painful, and not well endured” (p.161). The possibility that tickle elicits an unpleasant state was noted as far back as the ancient Greeks. Socrates suggested that tickling elicited pleasure but to a greater degree pain (cited by Gregory, 1924). Despite centuries of speculation, only a handful of empirical studies have investigated tickle, most within the past few years. For example, neuroscientists have employed light tickling in fMRI studies to explore the neural activation of anticipation of sensory stimuli (Carlsson, Petrovic, Skare, Petersson, & Ingvar, 2000; Blakemore, Wolpert, & Frith 1998). The remaining researchers have focused on trying to understand the nature of tickle. Observations such as those by Bacon have led some to propose tickle-induced smiling may have little to do with a positive emotional state such as amusement or happiness. Instead the tickle response may be a type of complex reflex or fixed action pattern (e.g. Black, 1982; Harris, 1999; Stearns, 1972), or perhaps a species-typical stereotyped motor pattern that requires a particular releasing stimulus (Provine, 1997). Recent findings provide some support for this view. First, while previous work has shown a warm-up effect of humorous stimuli (the first few jokes in a series are not as funny as later jokes), warm-up does not seem to transfer between humorous stimuli and tickle (Harris & Christenfeld, 1997). Second, ticklish laughter and smiling does not require the belief that another person is performing the tickling. Responses were as intense when people were alone and believed they were being tickled by a machine as when they were being tickled by another person (Harris & Christenfeld, 1999). Third, in Pavlovian conditioning, tickling has served as the unconditioned stimulus that elicits laughter (Newman, O’Grady, Ryan, & Hemmes, 1993) and tickle-induced smiling emerges in infants even when it has been not paired with playful interactions (Leuba, 1941). Facial Expressions 6 Despite this burgeoning interest in tickle, several questions remain unanswered. What is the connection between the facial expression of tickle and the internal subjective state? Is the smiling elicited during tickling completely disconnected from the internal emotional state as suggested by Bacon and advocates of a reflex explanation? Is the facial expression a mixture of pleasure and pain as claimed by Socrates? Do people who find tickle pleasurable display different facial expressions than those who find it unpleasant? Present Research The aim of this study was to explore these basic questions. The speculation that the tickle response is due to amusement has been based primarily on the assumption that the smiling that occurs during tickling is indeed the same as that occurs during humor. However, while only four of the studies described above specifically measured smiling/laughter during tickling; none of them closely examined these nonverbal displays to determine whether they differed from those evoked by humor. This study offers the first microanalysis of the facial movements that occur during tickling. It also systematically examined the emotional state that people reported experiencing during tickling, an aspect neglected in previous work. A within-subjects design was used to examine behavior and self-reported emotional responses of 84 subjects across three conditions: (1) being tickled for 10 seconds, (2) listening to a series of recorded comedy routines, and (3) immersing one hand in a bucket of circulating cold water for as long as tolerable. Comparing the facial expressions and self-report of the experience of tickle is of interest in its own right, and may shed light on the previously mentioned hypotheses regarding the nature of tickle. Including painful and humorous conditions enables us to examine whether tickle simply resembles amusement or has painful or unpleasant aspects. Facial Expressions 7 Method Subjects Eighty-four healthy University of California, San Diego students (61 females), who had not taken pain medicine, participated to fulfill a class requirement. Procedures Each subject participated alone and was exposed to three conditions: tickle, comedy, and pain. Order was counter-balanced across subjects. After each condition, the subject filled out an emotion inventory. Facial behavior was recorded by a videocamera placed in front of the subjects. Only the lens of the camera was exposed; the rest of the camera was hidden behind a large board, which contained colorful pictures. Tickle Condition. The female research assistant stood behind the subjects and tickled them on their sides (from the armpits to the waist) for 10 seconds. Subjects were informed that they could stop the tickling if the sensation became too intense. No subject asked to stop. Comedy Condition. Subjects listened to an audiotape of a series of twelve jokes by various comedians (e.g. Seinfeld, Cosby). The first 2 jokes were used as practice stimuli. Pain Condition. The subject’s left hand was immersed in a bucket of circulating cold water (1-5 Co). Subjects were instructed to press a button when they first started to feel pain and then to press it again when they could no longer tolerate the pain, at which point they withdrew their hand from the water. If the subject had not pressed the intolerable pain button after 3 minutes, the experimenter terminated the task. One subject continued for the entire 3 min. Facial Expressions 8 Dependent Measures Facial Action Coding. Subjects’ facial movements were coded using Ekman and Friesen’s Facial Action Coding System (FACS; 1978). FACS provides a method for objectively describing movement in the face. It catalogs distinct combinations of observable muscle movements into 44 numbered appearance changes called “action units” (AUs). Ten seconds of facial behavior were coded during each condition as follows: the 10 sec during tickling, the 10 sec immediately before removing the hand from the cold water; and one second following each of the punchlines of the ten jokes (a total of 10 sec). Self-report ratings. After experiencing each condition, subjects described their subjective states using a series of rating scales labeled with the names of emotions and feelings. They used a scale of 0 (not at all) to 7 (extremely) to rate how much they had felt: anxious, happy, angry, embarrassed, and amused. They similarly rated how much they found the experience unpleasant and painful. In the tickle condition, subjects also rated how ticklish and unpleasant they found the sensation of being tickled. At the end of the experiment subjects were asked, “Do you enjoy being tickled?” Results and Discussion Results of analysis of self-report ratings and facial activity are described separately, then compared. There were no sex differences on any of the measures except that men had higher amusement ratings and lower pain ratings. Women rated the tickle as more ticklish and unpleasant. Analysis of Self-report Ratings Self-reported ratings of the emotional state elicited during tickling (See Figure 1) appear to generally support Socrates’ suggestion that tickle is capable of eliciting both positive and negative affect. Paired two-tailed t-tests of each rated emotion were used to compare ratings during tickle to those Facial Expressions 9 during pain and humor. Happy and amused ratings for the tickle condition were significantly higher than those reported in the pain condition (t (83) = 9.70, p < .001; t (83) = 5.57, p < .001, respectively) and significantly lower than those reported in the humor condition (t (83) = 3.87, p < .001; t (83) = 5.11, p < .001, respectively). Anxious and unpleasant ratings for the tickle condition also fell between the pain and humor conditions; tickle elicited significantly higher ratings than humor stimuli (t (83) = 5.67, p < .001; t (83) = 4.03, p < .001, respectively) and significantly lower ratings than the pain stimulus (t (83) = 3.49, p < .002; t (83) = 19.52, p < .001, respectively). However, subjects described tickle more often as unpleasant rather than as painful. The tickle condition elicited virtually no self-reported anger but did elicit significantly more embarrassment than the pain (t (83) = 8.07, p < .001) or humor (t (83) = 8.29, p < .001) conditions. In short, based on people’s self-reports of their emotional experience, tickle does not appear to simply elicit the emotional state of amusement. Relative to the humor and pain conditions, tickle elicited an intermediate level of both positive and negative affect across individuals. Analysis of Facial Behavior Two analyses of facial behavior were performed. First, occurrence of individual AUs was analyzed. Second, smiles were classified by smile type and these types were compared across the three conditions. Individual AUs. Is facial behavior consistent with the suggestion of Socrates and Bacon that tickle elicits pain as well as pleasure? While withdrawal movements have been noted in support of this claim, no one has previously examined the face to determine whether it reflects the experience of unpleasantness. Table 1 displays the mean occurrence of each type of AU per event. An event is defined as a set of action units overlapping in time forming a configuration held on the face together Facial Expressions 10 before fading. Ekman (1997) suggests that the event, not the individual AU, is the appropriate unit of analysis. For example, co-occurrence of AU1 and AU4 typically characterizes distress expressions (e.g., fear, sadness). Inner brow raises (AU1) together with a lowered brow movement (AU4), accounted for a significantly greater number of the AUs in the pain condition than in the other two conditions. In support of Bacon and Socrates, several AUs were more common during both pain and tickle compared to humor. These include wrinkling the nose (AU9) and raising the upper lip (AU10), both of which are associated with the expression of disgust (Rozin, Lowery & Ebert, 1994). The lip stretch (AU20), which gives the appearance of a grimace, also was a more typical movement during pain and tickle, as was the lip press (AU24) and tightening of the eyelids (AU7). The present findings, disclosing that tickle and pain share some facial movements, provides behavioral support for the view that tickling elicits some negative affect or discomfort. Several of the AUs that were found to be proportionally more frequent in the pain and tickle conditions in the current work have also been found in previous work on pain. Prkachin (1992) examined facial behavior in response to four different types of pain elicitors. He concluded that four actions reflect a general pain expression: levator contraction (AU9/10), orbit tightening (AU6/7), brow lowering (AU4) and to a lesser extent eye closure (AU43). Tickle shared movements not only with pain but also with humor. Lips parting/ jaw dropping (AU 25/26) was more frequent in humor and tickle than in pain. AUs that comprise the Duchenne smile (AU6 and AU12) accounted for more of the movements in the humor and tickle conditions than in the pain condition. Past research sometimes combines the activation of AU6 and 7 (since they both function to tighten the region around the eye). However, the distinction between the two was kept in the current work since activation of 6 is important in the Duchenne smile but is also found in other emotions Facial Expressions 11 such as distress and sadness while AU7 can occur with anger and with fear (Ekman & Friesen, 1982). In the present work, AU6 was more frequent during tickle and humor while AU7 was more characteristic of pain and tickle. Smile Types. To determine whether tickle-induced smiling qualitatively differed from humorinduced smiling, we examined the degree to which different AUs co-occurred with smiling across conditions. Types of smiles were divided into four categories based upon the AUs observed. All smile types included AU12 and opening of the mouth and jaw (AU25/26). The first category was labeled a non-Duchenne smile, and consisted of pulling the lip corners back (AU12) without any other AU activity. The second category was the Duchenne smile, defined by the actions of AU6 + AU12 (cheek raise added). This has been considered the smile of felt pleasure or the “enjoyment smile” (Ekman & Friesen, 1982; Ekman, Davidson, & Friesen, 1990). The third category was a controlled smiled, defined as an AU12 together with another lower facial movement whose action functioned to counteract or obscure the smile. This was defined primarily as turning the lips down (AU15) or pressing the lips together (AU24). The fourth category was a mixed smile, defined as an AU12 occurring in the presence of AUs that are commonly associated with negative affective states (e.g. AU10, AU1+4, or AU20). As shown in Figure 2, the pattern of smile types varies across conditions. Duchenne smiles were found both in the tickle and humor conditions, but never in the pain condition (χ2= 56.84, df = 2, p < .001). Mixed smiles were the most frequent type of smile in the pain condition (51%) and were relatively common in the tickle condition (24%), but were relatively infrequent in the humor condition (10%): χ2= 81.35, df = 2, p < .001. The proportion of non-Duchenne and controlled smiles did not significantly differ across the three conditions. Facial Expressions 12 Given that Duchenne smiles and mixed smiles were the two types of smiles that showed a different pattern across conditions, the next analyses focused on the relationship of these two smiles with self-report of emotion. In the tickle condition, Duchenne smiles were correlated with amused ratings (r = .24, p < .03) but were more highly correlated with finding the tickle sensation ticklish (r = .29, p < .008) and unpleasant (r = .31, p < .005). Amused and unpleasant ratings were not correlated, (r = .07), suggesting that during tickling Duchenne smiles were associated with positive internal states for some subjects and negative internal states for others. Mixed smiles, like Duchenne smiles, were correlated with finding the tickle sensation ticklish (r = .27, p < .02) and unpleasant (r = .32, p < .004) and were also correlated with happy ratings (r = .25, p < .02). Happy ratings and unpleasant ratings were not correlated (r = -.05). In the humor condition, Duchenne smiles correlated with happy (r = .25, p < .03) and amused ratings (r = .32, p < .005), replicating previous work by Ekman and colleagues. Mixed smiles were also correlated with ratings of happy (r = .36, p < .002) and amused (r = .22, p = .05). In the pain condition, there were no Duchenne smiles and mixed smiles were not significantly correlated with any of the emotion rating scales. Interpretation of Results The findings that Duchenne smiles never occurred in the pain condition and were significantly correlated with amusement and happiness self-reports in the humor condition are consistent with previous work that has argued that the Duchenne smile is the smile associated with positive affect. Smiles during the pain condition were relatively infrequent; when these did occur, they were most likely to take the form of a mixed smile. One possible interpretation of mixed smiles is that they may be what Ekman and Friesen (1982) have referred to as masking smiles in work examining negative emotions. Facial Expressions 13 They suggested that "In a masking smile strong negative emotion is felt and an attempt is made to conceal those feelings by appearing positive" (p.244). In support of this interpretation, our study found that mixed smiles in the pain condition were not correlated with any of the self-report measures of emotion. Mixed smiles in the context of unambiguous pain may be the result of an individual’s coping style rather than a direct readout of an emotional state (Alvarado & Harris, 2001). The present findings showed that tickling is clearly capable of eliciting the Duchenne smile, which is normally associated with a positive hedonic state. However, mixed smiles were as common in the tickle condition as were Duchenne smiles. One possibility is that tickle elicits positive affect that then gives rise to smiling. In the case of the mixed smiles, the positive affect would be superimposed over the negative state elicited by the discomfort of tickling, suggesting a blend or mixture of emotions. However, our findings weigh against this interpretation: Duchenne smiles and mixed smiles were both correlated with finding the tickle sensation unpleasant and with positive affect ratings. Yet, unpleasantness ratings were not correlated with positive affect. In other words, some people showed Duchenne smiles and mixed smiles even though they did not report feeling happy or amused. An alternative view -based on the hypothesis that tickle is a type of complex reflex (Harris, 1999) -is that the smiling associated with tickling is not the result of a positive hedonic state. Instead, it is an automatic response that is elicited by a physical stimulus much like the kick elicited by tapping below the knee. According to this view, the negative AUs found during mixed smiles reflect the discomfort elicited during tickling just as they do during pain. However, the smile (AU12), whether imbedded in a Duchenne smile or a mixed smile, is an automatic behavior that is not reflective of any emotional reaction. This interpretation is supported by an additional finding of dissociation between smiling and self-reported pleasure. Open-ended responses to “Do you enjoy being tickled?” were Facial Expressions 14 categorized as yes (32%), mixed/neutral (32%), or no (36%). The three groups did not differ in number of Duchenne and mixed smiles. If anything people who dislike tickle produced slightly more Duchenne smiles (M = 1.21) than those who report liking it (M = .89). Is Tickle a Reflex or Fixed Action Pattern? The current findings support the view that tickle is a type of complex reflex or fixed action pattern. Interestingly, tickle shares several features with another phylogenetically old reflex, startle. One can no more tickle oneself than startle oneself. Both seem to require some element of surprise. Another similarity is that startle and tickle both appear to elicit facial expressions that resemble expressions that are usually elicited during emotional states. However, just as Ekman, Friesen, and Simons (1985) have proposed that the startle expression is not the result of an emotional state, we suggest that ticklish smiling does not arise from any positive emotional state. One might wonder why such a reflex or fixed action pattern would exist, a question that seems more straightforward for startle, with its orienting and defensive functions. One hypothesis is that tickling elicits smiling because it serves as a ready means for fostering a bond between caregiver and infant (Alexander, 1986; Fridlund & Loftis, 1990). The child smiles in response to tickling which causes the parent to smile which in turn elicits further smiling from the child. This reciprocity of smiling leads both parent and child to experience positive affect. This view, however, does not explain why the sensation of tickle also elicits a negative physical sensation. The unpleasant aspect of tickle has led some writers to suggest that the most ticklish areas are those that are most vulnerable in hand to hand combat, thus tickling confers an adaptive advantage by motivating one to protect these areas (Gregory, 1924; Hall & Allin, 1897). This would explain the pulling away and fending off movements frequently encountered during tickling. These researchers did Facial Expressions 15 not discuss why tickling elicits a facial expression that is usually associated with positive affect. One possibility is that the tickle smile may function as an appeasement display. Harris (1999) drawing on different aspects of these views recently proposed that tickle may elicit smiling to encourage conspecifics to perform the tickling and may elicit negative affect in the one being tickled in order to motivate the developing primate to avoid the tickling. By thus encouraging rough and tumble play, it may promote development and acquisition of combat skills. This view is consistent with Provine’s (2000) interesting suggestion that laughter first emerged from rough and tumble play in primates and only later became associated with humor in humans. Although these various views offer some intriguing suggestions, testing hypotheses regarding ultimate mechanisms is notoriously difficult. However, what does seem to be emerging from current research is that tickle is not merely a special case of amusement. In closing, we note that the present conclusion that ticklish smiling is not the result of a positive affective state does not mean that no positive emotions ever arise during tickling. Various aspects of the social setting (such as who does the tickling, how long it lasts, the pre-existing mood of the person tickled) are capable of eliciting a variety of reactions, some enjoyable and some unpleasant. For example, the common practice of “tickle torture”, in which several children hold down and tickle one child, can elicit anger whereas two new lovers tickling one another can promote enjoyment (see Provine, 2000 for descriptive data). Some of the confusion that has arisen over the relationship of smiling and laughter and affect during tickling may reflect an erroneous assumption that these positive aspects of the situation are responsible for the smiling observed in tickling. The present results, along with recent findings mentioned in the introduction, lend support to the notion that ticklish smiling may Facial Expressions 16 have no closer a connection to mirth and merriment than crying when cutting onions has to sorrow and sadness. Facial Expressions 17 ReferencesAlvarado, N. & Harris, C. (2001). Facial expressivity and coping styles. Manuscript inpreparation.Bacon, F. (1677). A Natural History, vii, 721-766.Black, D.W. (1984). Laughter. Journal of American Medical Association, 252, p. 2995-2998.Blakemore, S.J., Wolpert, D.M., & Frith, C.D. (1998). Central cancellation of self-producedtickle sensation. Nature Neuroscience, 1, 635-640.Carlsson, K., Predrag, P., Skare, S., Petersson, K.M., & Ingvar, M. (2000). Ticklingexpectations: Neural Processing in anticipation of a sensory stimulus. Journal of CognitiveNeuroscience, 12, 691-703.Craig, K. D.; Hyde, S. A.; Patrick, C. J. (1991). Genuine, suppressed and faked facialbehavior during exacerbation of chronic low back pain. Pain, 46, 161-171.Darwin, C. (1872/1965). The expressions of the emotions in man and animals. London: JohnMurray.Ekman, P. (1997). “Conclusion: What we have learned by measuring facial behavior.” In P.Ekman and E. Rosenberg (Eds.), What the face reveals (pp. 469-485). New York: Oxford UniversityPress.Ekman, P. & Friesen, W. (1978). Facial action coding system: A technique for themeasurement of facial movement. Palo Alto, CA: Consulting Psychologists Press.Ekman, P. & Friesen, W. (1982). Felt, false, and miserable smiles. Journal of NonverbalBehavior, 6, 238-252. Facial Expressions 18 Ekman, P., Friesen, W.V., & Simons, R.C. (1985). Is the startle reaction an emotion? Journalof Personality & Social Psychology, 49, 1416-1426.Ekman, P., Davidson, R.J., & Friesen, W.V. (1990). The Duchenne smile: Emotionalexpression and brain physiology: II. Journal of Personality & Social Psychology, 58, 342-353.Fridlund, A.J., & Loftis, J.M. (1990). Relations between tickling and humorous laugher:Preliminary support for the Darwin-Hecker hypothesis. Biological Psychology, 30, 141-150.Gregory, J.C. (1924). The Nature of Laughter. New York, NY: Harcourt, Brace, andCompany.Hall, G. S., and Allin, A. (1897). The psychology of tickling, laughing and the comic. TheAmerican Journal of Psychology, 9, 1-42.Harris, C. R. (1999). The Mystery of Ticklish Laughter. American Scientist, 87, 344-351.Harris, C. R., & Christenfeld, N. (1999). Can a machine tickle? Psychonomic Bulletin &Review, 6, 504-510.Harris, C. R., and Christenfeld, N. (1997). Humour, tickle and the Darwin-Hecker hypothesis.Cognition & Emotion, 11, 103-110.Keith-Spiegel, P. (1972). Early conceptions of humor: Varieties and issues (pp.4-39). In J.H.Goldstein & P.E. McGhee (Eds.), The Psychology of Humor. New York: Academic Press.Leuba, C. (1941). Tickling and laughter: Two genetic studies. Journal of Genetic Psychology,58, 201-209.Newman, B., O'Grady, M.A., Ryan, C.S., and Hemmes, N.S. (1993). Pavlovian conditioningof the tickle response of human subjects: temporal and delay conditioning. Perceptual and Motor Skills,77, 779-785. Facial Expressions 19 Panksepp, J. (2000). The riddle of laughter: Neural and psychoevolutionary underpinnings ofjoy. Current Directions in Psychological Science, 9, 183-186.Patrick, C.J., Craig, K.D., Prkachin, K. M. (1986). Observer judgments of acute pain: Facialaction determinants. Journal of Personality & Social Psychology, 50, 1291-1298.Prkachin, K.M. (1992). The consistency of facial expressions of pain: A comparison acrossmodalities. Pain, 51, 297-306.Provine, R. R. (1997). Yawns, laughs, smiles, tickles, and talking: Naturalistic and laboratorystudies of facial action and social communication (pp. 158-175). In The psychology of facial expression,ed. J.A. Russel and J.M. Fernandes-Dols. Cambridge: Cambridge University Press.Provine, R. R. (2000). Laughter: a scientific investigation. New York, NY: Viking.Schimmack, U. (2001). Pleasure, displeasure, and mixed feelings: Are semantic oppositesmutually exclusive? Cognition and Emotion, 15, 81-97.Stearns, F.R. (1972). Laughing. Springfield: Charles C. Thomas.Weisfeld, G. E. (1993). The adaptive value of humor and laughter. Ethology & Sociobiology,14, 141-169. Facial Expressions 20 FootnotesThere may be two types of tickle and the connection between the two types is unknown (Hall & Allin,1897; Harris, 1999). Knismesis feels like a “moving itch” and is elicited by a light, moving stimulus.The present work focuses on gargalesis, the laughter-inducing tickle elicited by a rapid, higher pressurestimulus applied to certain ticklish areas.2 Schimmack (2001) noted that the absence of a correlation may not be a strong test of whether twoemotional states can co-occur. He suggested an alternative test that examines the minimum intensity ofthe two states. If the states are incompatible, the value should approach 0. The min value of thepresent data is .67, suggesting that in this circumstance individuals did not report experiencing high levelsof both states during the same period.3 Min value = .61.4 Mixed smiles were infrequent in the humor condition (accounting for less than 10% of the smiles).When such smiles did occur, they were correlated with positive affect. One possibility is that mixedsmiles in pain and in humor have a different source. In humor such smiles may arise from positive affectaccompanied by negative evaluation of the comic stimuli (e.g. a joke that was funny but inappropriate).5 In the tickle and pain conditions, the correlation of pain and unpleasantness ratings with negative AUsdid not present a clear picture. Due to space limitations, these data are not presented here. Otherresearchers have noted a lack of correlation between self-report and specific pain AUs and havesuggested that different measures may assess different aspects of pain (Craig et al., 1991; Patrick,Craig, and Prkachin, 1986). Facial Expressions 21 Table 1Mean Occurrence of AUs Per Event Across Conditions