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Motivation and Emotion, Vol. 20, No. 2, 1996 Facial Feedback Hypotheses: Evidence, Implications, and Directions I Daniel N. McIntosh 2 This review evaluates four facial feedback hypotheses, each proposing a certain relation between the face and emotions. It addresses criticisms of the data, considers implications for emotional and social processes, and advises directions for future research. The current data support the following: Facial actions are sensitive to social context, yet correspond to the affective dimension of emotions; matches with specific emotions are unlikely. They modulate ongoing emotions, and initiate them. These two claims have received substantially improved support, in part due to studies controlling for effects of experimental demand and task difficulty. Facial action may influence the occurrence of specific emotions, not simply their valence and intensity. Facial action is not necessary for emotions. There are multiple and nonmutually exclusive plausible mechanisms for facial effects on emotions. Future work must focus on determining the relative contributions of these mechanisms, and the parameters of their effects on emotions. Smile when you read this! Proponents of facial feedback hypotheses claim that doing so cause you to like this article more, and make your mood more positive. Skeptics disagree. Despite a century of discussion of this question, research has been strongly evident for less than 25 years, and our knowledge regarding facial effects on emotion is changing rapidly. The most recent comprehensive reviews concluded that facial actions influence emotions (Adelmann & Zajonc, 1989; Manstead, 1988). Nonetheless, ques- tions about the interpretation of the data and the importance of the effect 1I appreciate the helpful comments of Harry Gollob, Greg McHugo, Catherine Reed, Craig Smith, and R. B. Zajonc on earlier drafts of this paper. 2Address all correspondence to Daniel N. Mclntosh, Department of Psychology, University of Denver, Denver, Colorado 80208. 121 0146-7239/96/060~0121509.50/~ © 1996 Plenum Publishing Corporation

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Motivation and Emotion, Vol. 20, No. 2, 1996

Facial Feedback Hypotheses: Evidence, Implications, and Directions I

Daniel N. McIntosh 2

This review evaluates four facial feedback hypotheses, each proposing a certain relation between the face and emotions. It addresses criticisms of the data, considers implications for emotional and social processes, and advises directions for future research. The current data support the following: Facial actions are sensitive to social context, yet correspond to the affective dimension o f emotions; matches with specific emotions are unlikely. They modulate ongoing emotions, and initiate them. These two claims have received substantially improved support, in part due to studies controlling for effects o f experimental demand and task difficulty. Facial action may influence the occurrence of specific emotions, not simply their valence and intensity. Facial action is not necessary for emotions. There are multiple and nonmutually exclusive plausible mechanisms for facial effects on emotions. Future work must focus on determining the relative contributions of these mechanisms, and the parameters of their effects on emotions.

Smile when you read this! Proponents of facial feedback hypotheses claim that doing so cause you to like this article more, and make your mood more positive. Skeptics disagree. Despite a century of discussion of this question, research has been strongly evident for less than 25 years, and our knowledge regarding facial effects on emotion is changing rapidly. The most recent comprehensive reviews concluded that facial actions influence emotions (Adelmann & Zajonc, 1989; Manstead, 1988). Nonetheless, ques- tions about the interpretation of the data and the importance of the effect

1I appreciate the helpful comments of Harry Gollob, Greg McHugo, Catherine Reed, Craig Smith, and R. B. Zajonc on earlier drafts of this paper.

2Address all correspondence to Daniel N. Mclntosh, Department of Psychology, University of Denver, Denver, Colorado 80208.

121

0146-7239/96/060~0121509.50/~ © 1996 Plenum Publishing Corporation

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keep the idea controversial (Buck, 1984; Fridlund, 1994; Matsumoto, 1987). Further, the nature and mechanisms of the phenomenon are debated even among supporters. Less discussed are reasons why psychologists should care about this phenomenon.

EVOLUTION OF FACIAL FEEDBACK HYPOTHESES

The idea that the face influences emotions has adapted and mutated over the years, providing variation and viability to its descendants. Psycholo- gists studying the effects of the face on emotions trace their inspiration to Charles Darwin and William James. Darwin (1872/1955) noted that enhanc- ing or inhibiting the expression of an emotion alters the intensity of that emotion. He wrote this in order to explain why expression is an important topic for, and explicable from, a naturalist perspective; he also noted that emotional expressions serve a social-communicative function. However, so- matic influence on emotion is neither a primary concern, nor integral to his theorizing. James (1890/1950) went further, proposing that physiological changes, including facial action, a r e the emotions. The body changes, and the subjective experience of emotion follows. Somatic input is essential to the theory. This contrast is one root of the debate surrounding facial feed- back. For the "Jamesian" emotions theorists, a small effect is important, as it pertains to understanding details of emotions processes. Others typi- cally consider the effect interesting only if it plays a role in "everyday phe- nomena" (Fridlund, 1994, p. 182).

Although a strong critique by Cannon (1927) muted consideration of feedback, two ideas revived interest in the effects of facial movement in the 1960s. First, Tomkins (1962) gave the face a primary role in his emo- tions theory: "The face expresses affect, both to others, and to the self, via feedback, which is more rapid and more complex than any stimulation of which the slower moving visceral organs are capable" (p. 205). This avoided Cannon's criticisms by making visceral changes unnecessary, and by placing the focus on a part of the body relatively untouched by Cannon's analysis (see also Gellhorn, 1964). Building on this, Izard (1971) indicated that dis- crete facial configurations are a primary determinant of the quality of the felt emotion. As with James, facial action is a fundamental component in this approach.

The second idea is based on the two-factor theory of emotion, in which intensity of emotion is associated with generalized physiological arousal, and the specific emotion is mediated by cognitive processes (Schachter & Singer, 1962). Bern (1967) built on this notion by discussing how emotional experience may be based in part on cognitive self-perception processes. This theory suggests that facial configuration may be one source of infor-

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mation used in making self-attributions of emotions (Laird, 1974), but facial effects on emotion are not fundamental to it.

A decade later, these two theoretical branches bore empirical fruit. Laird (1974) developed the self-perception view of emotional experience and tested the role facial action plays. He indicated that if people are in- duced to express an emotion, they may then feel that emotion. Lanzetta and colleagues found that individuals who feigned not experiencing pain during electric shock showed fewer physiological and subjective pain re- sponses than those who pretended to be experiencing unbearable pain (Lanzetta, Cartwright-Smith, & Kleck, 1976; see also Kleck, Vaughan, Cart- wright-Smith, Vaughan, Colby, & Lanzetta, 1976).

By the late 1970s, this theorizing and data gave currency to the idea that facial movement could influence emotions. The term facial feedback hypothesis was coined because the effect had become somewhat separated from its theoretical parents (Ellsworth & Tourangeau, 1981; Tourangeau & Ellsworth, 1979). The label carries connotations regarding the nature of the process. For consistency's sake, I use the term to denote the general area of analysis, but note that not all proposed mechanisms assume that facial effects involve feedback. Further, there are variations on what rela- tion is suggested by the term. The diversity of hypotheses labeled "facial feedback" has confused the debate about such effects, making the associa- tion between facial patterns and emotions less clear. However, careful con- sideration of the data supports the existence of some specific relations, and provides information relevant to emotions (and other) processes. It is time to move past demonstrations of an effect, and to use the data as a basis for addressing more sophisticated questions and applications. The first step in this process is clarifying what is known.

EVALUATION OF CONTEMPORARY FACIAL FEEDBACK HYPOTHESES

There are four common general proposals related to facial feedback. They may not be equally valid. To best grasp what we know about this process, it is important to specify which hypothesis is being tested. I have organized this review around the four questions. Three are based on the scheme used in Adelmann and Zajonc's (1989) review, although the cate- gorization of studies is slightly different. The first does not imply causality: (1) Does facial configuration correspond to emotions? The next two hold facial actions as able to influence emotions: (2) Does facial movement modulate emotions in the presence of other emotional stimuli; and (3) can facial action initiate emotions, even with no (other) emotional stimuli pre-

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sent? The last question follows Tourangeau and Ellsworth (1979): (4) Is facial action necessary for the presence of emotions? Note that causality is not unavoidably implied in the necessity hypothesis. It may be that par- titular facial configurations are an essential component of emotions, but serve no causal function. Cutting across all four questions is the issue of what emotional outcome is supported. Is the face associated with the de- gree of positive or negative affect only (dimensional versions), or is there a link to specific emotions--anger rather than sadness, for example (cate- gorical versions)? Tests of the hypotheses pertained mostly to the dimen- sional question through the mid-1980s (Winton, 1986). One question for the present review, then, is to consider the degree of support for the cate- gorical versions evident since that time.

Instead of noting every study, I emphasize studies from the late 1980's onwards, as the last comprehensive reviews were published then. Further, research since that time has addressed primary methodolic criticisms and begun to fill some conceptual gaps; I will focus on what has been learned. I spend little space on between-subjects versions of the hypotheses. These hold that those individuals who are more expressive should experience more intense emotions. There is no such positive association. People who tend to express more do not feel more, in fact, their physiology tends to be less reactive (Buck, 1980; e.g., Lanzetta & Kleck, 1970). Although re- lated to the phenomenon at hand, this area deserves a separate review. The within-subjects versions are the hypotheses presently at issue. Within individuals, does facial action correspond to or cause changes in experience and physiology?

Do Facial Actions Correspond to Emotions?

This hypothesis simply states that facial patterns covary with emotions. Supportive studies find that emotion associates with visually observed facial activity (Buck, Savin, Miller, & Caul, 1972; Ekman, Friesen, & Ancoli, 1980) and facial electromyography (EMG; Cacioppo, Petty, Losch, & Kim, 1986; Dimberg 1988). EMG not only changes as a result of manipulation of emotions (i.e., the probability of a particular EMG pattern given the associated affective state is high), but also predicts self-reported emotions (i.e., the probability of an affective state is high given a particular EMG state) (Cacioppo, Martzke, Petty, & Tassinary, 1988).

These studies support strongly the dimensional version of the corre- spondence hypothesis. Although many studies simply have not checked for categorical effects (i.e., within-valence differences), most that did have been largely unsuccessful or inconsistent (Camras, Holland, & Patterson, 1993;

Facial Feedback Hypotheses 125

e.g., Brown & Schwartz, 1980; Fridlund, Schwartz, & Fowler, 1984; Tourangeau & Ellsworth, 1979). Note that the lack of correspondence be- tween specific facial patterns and particular emotional experiences does not contradict the data showing that people can identify archetypal facial pat- terns associated with categorized emotions (see, e.g., Ekman, 1994). Know- ing that a certain pattern is typical of anger, for example, is different than consistently possessing that pattern when anger is felt.

The difficulty in finding categorical correspondence suggests a funda- mental problem. There may be too many antecedents and contexts for fa- cial movement for one-to-one relations between muscle patterns and particular emotions to be the rule ('lhssinary & Cacioppo, 1992). Note that this analysis leaves room for a modulating or initiating function of facial action. Many variables may influence facial action, reducing correspon- dence. Nonetheless, particular facial patterns may still sway emotional state. The lack of correspondence simply suggests nonfacial influences on emo- tion, and nonemotional influences on facial movement.

The social context of the actor is one variable that affects facial dis- plays. A likely primary function of facial motion is communication of inner state or intent to others. Buck (1980, 1994), for example, does a nice job portraying how facial actions are influenced by both internal states and social factors. Going further, some (e.g., Fridlund, 1994) argue that facial configurations are a function of social context or communicative intent only, not emotional state. Consistent with the notion that there is strong social effect on facial activity, audience effects on smiles are found as early as 10 months of age (Jones, Collins, & Hong, 1991; for adult data, see Chovil, 1991, Kraut & Johnston, 1979). There are two problems with the position that social considerations are the sole influence on facial pattern- ing, however. To begin, facial action can vary as a function of affective state even when the movements are too small for observers to notice (Ca- cioppo, Bush, & Tassinary, 1992). Thus, studies finding no visible changes in connection with emotional stimuli or state are not evidence that facial action and emotions are independent. More important, social modulation does not preclude a connection to emotional state. Recent work demon- strates that facial movement is influenced by both factors. Cacioppo et al. (1992) found that:(1) EMG varied with the affective content of slides even when participants viewed them privately;(2) facial responses were similar during social vs. asocial emotional stimuli; and (3) movement varied with affective tone of stimuli even when individuals were told to inhibit expres- sion to avoid communicating their emotional responses. Hess, Banse, & Kappas (1995) compared women's reactions to films varying in emotional strength under conditions varying in sociality and interpersonal relationship. Facial action was influenced by both social factors and emotional intensity

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(see also Kraut, 1982). The data show a clear correspondence in valence between affective state and facial patterns. A categorical association be- tween specific emotions and patterns is difficult to find, perhaps because of other (e.g., social) influences on facial motion.

Given the above findings, what are some directions for future work? One is to follow the lead of Smith (1989), and search for correspondences between specific facial movements (e.g., the eyebrow frown), and distinct components of emotions (e.g., appraisals and physical changes). This level of analysis may allow for more precise descriptions of what factors are as- sociated with which facial actions, and which aspects of emotions. The di- mensional findings are consistent with this approach; extending this level of analysis to other dimensions and facial movements has potential to un- tangle the mutual influences affecting the correspondence between facial actions and emotional processes.

Does Facial Movement Modulate Emotions?

The modulation hypothesis states that facial action can affect emotions during ongoing emotional experiences. This may refer to intensity (e.g., frowning when already sad might make one sadder) or quality of experience (e.g., smiling when sad may make the sadness bittersweet). However, tests of this hypothesis have focused on changes in intensity. The emotion theo- ries that formed the early basis for facial feedback focused on the role of the face in ongoing emotional experience (Izard, 1981; Tomkins, 1981). Thus, demonstrations of modulation are important for evaluating these views. Additionally, this is a potential causal function, and the issue of cau- sality is implied in folk theories, in how people interpreted the initial theo- ries (Ellsworth & Tourangeau, 1981), by Izard's (1981, 1990) propositions, and by the earliest studies. Further, if a causal role is established, this in- creases the practical implications of the phenomenon (Tourangeau & Ellsworth, 1979). Whether it be by modulation or initiation, this is the cru- cial question regarding facial feedback: Does the face do more than express emotions; does it also change them?

When participants are instructed how to alter their faces muscle by muscle, their responses to stimuli are sometimes influenced by the pattern in which their faces are set (Laird, 1974; Rutledge & Hupka, 1985), but not always (Tourangeau & Ellsworth, 1979). Exaggeration or inhibition of expressions while experiencing stimuli also provide uneven support for the modulation hypothesis (Bush, Barr, McHugo, & Lanzetta, 1989; McCanne & Anderson, 1987; Ohira & Kurono, 1993). Concerns about demand effects

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(Buck, 1980; Manstead, 1988) and questions about the support for the cate- gorical hypothesis (Winton, 1986) plague this work.

A recent study provides more solid support for the modulation hy- pothesis, while also addressing persistent concerns. Using imagery to gen- erate emotions, Hess, Kappas, McHugo, Lanzetta, and Kleck (1992) compared the time it took individuals to reach four emotional states during three conditions. In the "Feel" condition participants generated an emo- tion. For the "Feel-and-Show" condition they generated the target emotion and displayed the facial configuration consistent with it. In the "Show" con- dition they posed an expression. In the Feel condition, subjects took longer to achieve the emotion state than in the Feel-and-Show condition. The ad- dition of facial action facilitated the self-generation of the emotions. These data address several concerns. First, demand is an unlikely explanation for the effects, as the measure is indirect, and participants did not know that response latency was being assessed. Second, perceived task difficulty was not associated with stronger negative and weaker positive emotional feel- ings. Finally, because two positive and two negative emotional states were used, and there were differences in self-reported emotions consistent with facial expression, it provides evidence for the categorical version of the hy- pothesis.

When physiological measures are used, it is implausible that partici- pants are simply conforming to experimental demand (Buck, 1980). Lan- zetta and colleagues (Colby, Lanzetta, & Kleck, 1977; Kleck et al., 1976; Lanzetta et al., 1976) report that alterations of pain expressions during shock influence both electrodermal response (EDR) and subjective report. These studies show that facial and bodily action influence physiological and subjective status. Although pain is not a clearly emotional outcome (Buck, 1980; Tourangeau & Ellsworth, 1979), the studies reported by Lanzetta et al. included EDR assessment during anticipation of electric shock. Facial posing during this anxiety-provoking interval influenced EDR in the same way. Other research also finds effects on emotional responses, although the support is uneven (Ianni, Stettner, & Freedman, 1986; Zuckerman, Klorman, & Larrance, 1981).

Some recent studies address the issue of experimental demand by al- tering facial action by having people engage in emotion-analogous facial movement. Effects of facial configuration on responses provide support for the modulating function. Strack, Martin, & Stepper (1988) instructed par- ticipants to hold a pen in their teeth, lips, or nondominant hand. The first produces a smile-like pattern, the second inhibits it, and the third is a con- trol condition. Individuals found cartoons more humorous during the simu- lated smile, and less humorous when their smiles were suppressed. Zajonc, Murphy, and Inglehart (1989) created facial actions analogous to positive

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and negative configurations by having participants pronounce vowels. In one study, speakers read aloud stories with either a high frequency of the vowel ~/, or none of that vowel. Voicing g/results in facial activity similar to a frown or scowl. If facial action alters the affective impact of the stories, then the participants should experience more negative feelings during the high-ii story than during the no-t~ one. They did. Larsen, Kasimatis, and Frey (1992) attached golf tees to participants' brows. Contraction of the corrugator supercilii causes the tips of the two tees to touch, and produces an action generally associated with sad facial expressions, among others. When individuals kept the tees together, they reported that sad photo- graphs made them sadder than when they were instructed to keep the tees apart. They found no differences between the tasks on rated difficulty, sug- gesting that this is not the reason for the different emotion rating.

In summary, reviews completed in the late 1980s concluded that facial action modulated ongoing emotions (Adelmann & Zajonc, 1989; Manstead, 1988). Since these reviews, additional studies have addressed this issue, and the majority have been supportive. The greater number of scientists and methods that find the effect increases confidence that it is not artifactual. Further, the more recent positive efforts have responded to the methodo- logical criticisms of the earlier ones, and address directly issues of experi- mental demand, effort effects, and categorical effects. Only work on the latter, however, begins to address the issue of qualitative (vs. intensity) modulation; future work should address this more directly. Despite the stronger empirical basis, however, the number of studies with nonsignificant results suggests that the effect is not large, the outcome may be moderated by unmeasured variables, some research is using unreliable measures or invalid manipulations, or some combination of these. One task is to estab- lish clearly conditions under which facial action modulates emotional ex- perience.

Can Facial Action Initiate Emotions

The second causal facial feedback hypothesis holds that people can initiate emotions through facial movement. This has often been considered a stronger hypothesis than modulation; however, initiating an emotional state when none is present is not necessarily a more powerful effect than altering an extant state elicited by other stimuli.

Several studies demonstrate initiation (e.g., Duncan & Laird, 1977, 1980), and more recently, categorical effects have been addressed. In one study, participants contracted muscles involved in fear, anger, sadness, and disgust, in turn, and rated their emotions subsequent to each contraction

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on these feelings, plus happiness, surprise, agreeableness, and interest (Du- clos, Laird, Schneider, Sexter, Stem, & Van Lighten, 1989). Fear ratings were significantly higher during the fear expression than in any of the other three, and sad was higher during the sad pattern. Anger and disgust were not significantly differentiated from each other, but were from fear and sadness. These data suggest that facial patterns can sometimes initiate emo- tion-specific experience (see also Laird, Cuniff, Sheehan, Shulman, & Strum, 1989). However, this work is vulnerable to potential experimental demand effects.

Physiological measures are less likely to be products of demand, and there is some evidence that physiology is altered by facial manipulations. An early demonstration of autonomic outcomes of facial patterns was re- ported by Ekman, Levenson, and Friesen (1983). With replication, however, the number of physiologic changes that reliably differ with facial expression has diminished (Zajonc & Mclntosh, 1992). Most consistently produced are lower heart rate (HR) increases during the disgust facial pattern than dur- ing anger, fear, and sadness, and larger increases in finger temperature during the anger configuration than in fear (Levenson, Ekman, & Friesen, 1990; see Shortt, Bush, McCabe, Gottman, & Katz, 1994, for a partial rep- lication; cf Tourangeau & Ellsworth, 1979).

Levenson et al. (1990) collected information on participants' subjective experiences during facial expressions. Facial configurations produced self- reports of the associated emotion on a significant proportion of trials. Al- though the muscle-by-muscle manipulation may cause some experimental demand to report the associated emotion, the physiological differentiation they found makes this less plausible. The connection of these outcomes to facial patterning is bolstered by the finding that when participants' faces best matched prototypical emotional expressions, the physiological differ- ences were strongest, and self-reported emotions most evident. In one ex- periment, Levenson et al. address the concern that physiological differences are related to variations in the difficulty required to pose the expression, rather than emotion produced as a result of the expression. No correlations between difficulty and the magnitude of physiological change were signifi- cant, and sorting the emotional expressions by difficulty did not produce groups that matched sets found when grouping by autonomic nervous sys- tem (ANS) data. Differential effort is thus not a likely explanation for the ANS results.

Another example of facial actions initiating emotions is reported by Zajonc et al. (1989). They had individuals pronounce /i (analogous to a scowl) or o (relaxed face) for one minute. The phoneme i/ caused a sig- nificant increase in forehead temperature, which has been associated with negative feelings (e.g., Mclntosh, Zajonc, Vig, & Emerick, in press; Zajonc,

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Murphy, & Mclntosh, 1993; see discussion of the Vascular Theory of Emo- tional Efference, below). Participants liked the o sound better and rated it as more pleasant than a. In another study, participants repeated several vowel sounds. Voicing/i increased forehead temperature, ah, and e (which produces a smile analog) decreased it. The least liked sound was ti; ah and e were liked most. The findings have been replicated, with the effect of voicing the vowels on mood remaining when level of difficulty of speaking them is statistically controlled (Mclntosh et al., in press).

Further evidence for an initiatory function of facial action is provided by Hess et al. (1992). Participants' heart-rate patterns were consistent across conditions in which they were asked to simply feel an emotion, sim- ply display it, or do both. Individuals physiologically responded in the dis- play-only condition in ways similar to the conditions in which they were to feel the emotion. Also, they reported feeling emotions when they were asked to display an emotion, but not to feel it. This study gives evidence of within-valence differentiation, providing support for the categorical ver- sion of the initiation hypothesis.

A new type of data supporting the initiating hypothesis has recently emerged. Based on brain lateralization of emotions (Davidson, 1992), Schiff and Lamon (1989; Schiff, Esses, & Lamon, 1992) examined the influence of unilateral facial action. Coders blind to condition rated the number and valence of emotion propositions used by participants in telling stories based on mood sensitive pictures from the Thematic Apperception Test (TAT); there is little chance that demand characteristics influenced these data. Par- ticipants tended to feel sad or depressed when contracting the left comer of their mouths. Following a right facial half-smile, they felt positive and energetic. Although Wissing and Wessels (1992) replicated these results, the effect may not occur among women.

In summary, support for the initiation hypothesis has been slower to obtain than for correspondence and modulation. Recent work, however, provides stronger evidence for categorical and dimensional versions using a variety of manipulations, and both self-report and physiological outcomes.

Is Facial Action Necessary for Emotions?

The necessity hypothesis states that emotions cannot occur without fa- cial activation. Although it has tended to be thought of as indicating that facial movement is a necessary cause, it may also refer to facial changes as being an inextricable component of emotions, without such expressions themselves being causal. The latter is essentially a strong correspondence hypothesis. Thus, the low association between categories of emotions and

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facial patterns argues against this position. More generally, people experi- ence emotions during times of facial paralysis, most commonly in REM dreaming when there is striate muscle paralysis (see Fridlund, 1994, for expanded examples). These occurrences make it difficult to maintain this hypothesis.

However, one version has not been empirically refuted, largely because it is difficult to test. Perhaps central nervous system (CNS) representations of facial expressions can meet the hypothesized need for such patterns with- out actual facial motion (Izard, 1977, 1990; Tomkins, 1962; cf Damasio's, 1994, somatic-marker hypothesis). Facial action or a neurocognitive repre- sentation of facial action may be necessary for emotions. It is not clear how this is functionally different than a completely central approach, except that it may predict different consequences of damage to particular brain regions, as alternate structures might be necessary for emotional experience if representations are needed than if they are not.

Recurring Criticisms of Facial Feedback Studies

Fridlund (1994) has organized several of the frequent concerns regard- ing facial feedback data. First, studies often contain implicit suggestions to participants about how they should act (Buck, 1980). As detailed above, recent work makes it unlikely that participants know what is expected and respond in ways consistent with the hypotheses. Regarding dependent vari- ables, the physiological data would be difficult for subjects to generate in response to experimental demand, and the individual differences in re- sponse to the manipulations do not follow a pattern expected if experi- mental demand were the cause (Laird, 1984). Further, the latency measure (Hess et al., 1992) and TAT procedure (Schiff & Lamon, 1989) are indi- cators of effects not sensitive to demand. On the manipulation side, several studies have used tasks that are unlikely to cue the participants as to the expected response (e.g., Strack et al., 1988; Zajonc et al., 1989).

Second, Fridlund (1994) suggests that these just mentioned facial tasks (e.g., holding a pen in one's teeth) are silly or embarrassing, and this is what causes the changes in emotion. However, that both negative and posi- tive affective changes result from the tasks makes this confound less plau- sible. For example, why does voicing e make one feel silly, and voicing a make one embarrassed, and not the reverse; why is reading a story with many// 's more aversive than humorous?

The third concern is the confounding of negative faces with difficulty. Because people can smile using only one muscle, the zygomaticus major which pulls the corners of the mouth up, and negative patterns need acti-

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vation and coordination of more than one muscle, participants may like the smile conditions better simply because they are easier (Fridlund, 1994). This criticism is refuted by the studies that find reports of effort or difficulty to be unrelated to the manipulation or emotion. Further, smiles utilizing two muscles (adding the orbicularis oculi, which crinkles the corners of the eyes) are more associated with positive affect than those using only the one (Ekman, 1992). This should not be the case if effort is the cause of more negative feelings.

Fourth, specific to those studies in which people modify their expres- sions during ongoing emotional experiences, those told to modify their ex- pressions may regulate their facial configuration by doing things (e.g., producing mental images) that also modify feelings. As there are several affirmative studies that do not use this manipulation, it is not a strong cri- tique of the hypotheses.

Summary: The Status of Facial Feedback Research

Recent studies address long-standing criticisms of facial feedback stud- ies, and provide a firmer foundation on which to evaluate the propositions. Especially in the case of the initiation hypothesis, recent work has dramati- cally increased the supportive evidence. Further, additional support for categorical effects is emerging. Nonetheless, the phenomena remain elu- sive. Despite the stronger empirical bases for the effects, research on facial feedback hypotheses leave a number of significant questions unanswered. Scholars need to evaluate conditions under which facial movement alters emotions, the mechanisms by which they do so, and the size of the effect under different conditions and by varying mechanisms. Further, the impli- cations of these phenomena need exploration. These issues constitute the necessary next area of scientific focus.

POSSIBLE MECHANISMS FOR FACIAL EFFECTS ON EMOTIONS

The primary research question should now be how facial feedback in- fluences emotions. One way to categorize mechanisms is by whether they are part of an emotions theory, or whether the effects are due to a more general process. The Jamesian camp holds that the influence of facial ac- tion on emotions is the result of the emotions system (e.g., Ekman, 1992; Izard, 1971; Tomkins, 1962). For the others, the theoretical focus is on more general processes (e.g., Buck, 1980; Fridlund; 1994; Laird, 1974). With the exception of Laird, those supporting the latter mechanisms view the effects

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as minor. The Jamesian group views even minor effects as important, due to their connection to understanding human emotional processes.

"Jamesian" Mechanisms: Facial Feedback as Part of Emotions Theories

CNS Connections. The dominant emotions-theory view of facial feed- back effects sees facial movements as part of the package of events that make up each emotion, or emotion program. These hypothesized programs are viewed as coordinating people's responses to emotion-eliciting situ- ations; they suppose a connection between the motor cortex and other parts of the brain (especially the limbic region; Kelley & Stinus, 1984) involved in physiological changes during emotions (Ekman, 1992; Levenson et al., 1990). Activating one part of the response set is thought to stimulate the others. If voluntary expressive actions simulate the innate emotional con- figuration, then the expression-specific feeling state may be initiated (Izard, 1990). Neural tracts may lead from facial muscles or skin to an integration center after the expression is produced, or the feedback may occur earlier, for example in the firing of the muscles (Matsumoto & Lee, 1993). Leven- son et al. (1990) think it likely that commands from the motor cortex to the facial nucleus are accompanied by parallel signals to the ANS. Damasio (1994) describes a neural network by which bodily states provide the input for the subjective feelings associated with emotions.

Obviously, there is opportunity for much empirical specification. Stud- ies of people with spinal lesions, lesions in the distal facial nerve tracts, or temporary neuromuscular blocks would address these possibilities (Matsu- moto & Lee, 1993). For example, people with spinal damage may be more subjectively emotionally excitable since the injury, yet experience less so- matic emotional responses (Bemlond, Nieuwenhuyse, Fasotti, & Schuer- man, 1991). Emotions are multicomponential phenomena, involving subjective state and a variety of physical events. Examining the effects of damage to part of the system provides data on the organization of the system. The report of Bermond et al. (1991) shows that aspects of emotions can be altered by physical damage, but that the changes are not always coordinated among components of emotions.

One concern with many CNS approaches is that they are based heavily on the evidence for facial action creating specific, categorical, emotion-re- lated patterns of ANS response. If facial action is conceived as starting neurophysiological states corresponding to emotions, this presupposes the existence of such patterns. However, it is difficult to say whether the ANS changes caused by facial action are emotional. Not all methods of gener- ating facial actions and of inducing emotions consistently show ANS pat-

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terns (Cacioppo, Klein, Berntson, & Hatfield, 1993; Zajonc & McIntosh, 1992)

Some theorists may not expect a high degree of consistency, however. One theory indicates that only facial muscle patterns that closely match highly specific configurations should induce emotions (Hager & Ekman, 1981; Levenson et al., 1990). Inexact or partial replications of emotional expressions should not, thus, induce the emotion or cause the physiological changes. In Izard's (1990) scheme, partial activation may cause the feeling state, but only if other areas of the face are not sending signals for other emotions. Note, however, that it may be that central processes are the key to facial feedback effects, even if current categorical theories of emotions are incorrect; it would simply require some modification of some CNS theo- ries.

Work on the effects of unilateral muscular contractions is also based on a CNS connection between facial action and emotion. This research focuses on the subjective experience of emotion, rather than physiological changes. Results are consistent with studies of brain lateralization of emo- tion (Davidson, 1992). Integrating these methods will provide information on brain functioning in emotions and on the parameters of CNS-face-emo- tion connections.

Note that Izard's (1971, 1977) view differs from the purely central views (Ekman, 1992; Levenson et al., 1990), as peripheral feedback plays an important role. Izard (1990) notes that mechanoreceptors in facial skin respond vigorously to facial muscle movement and are sensitive to the slightest movement. It is this patterning that provides distinctions among emotions. The next proposed mechanism also goes beyond purely central mechanisms.

The Vascular Theory of Emotional Efference (I/TEE). Zajonc and col- leagues (Zajonc & McIntosh, 1992; Zajonc et al., 1989, 1993) present a manner by which affect can be altered via facial action that does not rely on self-perception, cognitive appraisal, or activation of hypothesized CNS emotion programs. Brain temperature is influenced by the cavernous sinus, a venous configuration that envelops the internal carotid just before the carotid enters the brain. Air inhaled through the nose cools the blood of the cavernous sinus during normal breathing. Thus, nasal breathing cools the brain (Kluger & D'Alecy, 1975). VTEE assumes that cooling of the brain is hedonically positive (perhaps due to temperature effects on neuro- chemical processes). Indeed, direct cooling of the hypothalamus in rats leads to the same behavior demonstrated by rats receiving pleasurable elec- trical stimulation (Berridge & Zajonc, 1991).

In humans, there is evidence for the postulated chain of events. Be- cause facial actions that resemble emotional patterns influence the amount

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of air inhaled via the nose (Mclntosh et al., in press), they may have af- fective consequences. Repeatedly voicing//(producing a scowl) decreases the amount of air individuals inhale through the nose, leads to increased temperature at specific forehead points (a measure of brain temperature increase; see Mclntosh et al., in press for discussion), and generates nega- tive affect (Mclntosh et al., in press; Zajonc et al., 1989). Direct manipu- lation of breathing (e.g., pinching the nose shut) alters forehead temperature and affect (Mclntosh et al., in press), and changing the tem- perature of air inhaled changes forehead temperature and affect (Zajonc et al., 1989). This mechanism explains dimensional effects of facial move- ment only, and does not predict ANS changes following facial action.

"Darwinian" Mechanisms: Facial Feedback as By-Product

Conditioning. Specific facial expressions may become conditioned to certain subjective or physiological states. The typical presence of a smile when one is happy, for example, may cause the smile to become a classically conditioned stimulus for happiness. Involuntary expressions are likely to be more strongly connected to emotional responses than voluntary ones, as the former will more consistently be tied to the emotion; voluntary expres- sions may be formed, exaggerated, and suppressed based on social context (Buck, 1980). This view can account for facial effects on subjective expe- rience and most physiological changes, both dimensional and categorical effects, and modulation and initiation. Further, it is also consistent with the differences found in between-subjects vs. within-subjects tests of the hypothesis (Buck, 1980). Two findings suggest that conditioning is not the sole explanation for facial feedback data, however. First, it is not clear using this explanation why a muscle contraction on the left side of the body evokes a different subjective state than the same movement on the right side, given that movements on both sides of the face are consistently paired with the state. Second, it is difficult to consider pairing of emotion and expression to be the sole reason for the newer data supporting categorical effects of facial action when there is such variable correspondence between expression and discrete emotions.

Self-Perception. A second approach that predicts emotional effects of facial action is self-perception theory (Bem, 1967). From this perspective, the face provides data to the person regarding what he or she is feeling. Findings for both initiation and modulation are consistent with this model. Because this model predicts categorical effects, those results are especially important (Duclos et al., 1989); previous difficulty in finding them has caused some to doubt this mechanism (Winton, 1986). The effects of uni-

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lateral contractions and emotion-analog tasks (e.g., pen holding) are some- what inconsistent with this theory. For example, Strack et al. (1988) point out that their findings using oral pen holding counter a self-perception in- terpretation, because subjects' attention is drawn away from the face, and the facial configuration is constrained which should lead to participants dis- counting its effect.

Dramaturgy. Fridlund (1994) describes a dramaturgical route by which facial action could lead to altered emotions. People may use sensations from their faces to assume a role. They then might recruit memories or images to induce the emotion consistent with that role. This shares with the self-perception mechanism the idea of the face as data used by the person, but instead of the information being related to how one is feeling, it is instead relevant to how one should be acting. For example using an example from Laird's (1974) study, when a person is "instructed to move facial muscles to form a smile at a Ku Klux Klan slide [this person] is being asked implicitly to take an amused stance toward them" (Fridlund, 1994, pp. 178-179). If one forms an angry face, it follows, one will take on an angry role, which may involve acting angry by making a fist, yelling, and perhaps thinking angry thoughts.

Note that Fridlund (1994) separates the behavior from the emotion; "acting" angry is not "is" angry. This may be a problematic distinction, in that the action may lead to experience, even if experience incongruent with the socially-expected action is suggested. In one study, subjects asked under hypnosis to display one emotion and experience another reported being unable to experience one incongruent with their expressions (Pasquarelli & Bull, 1951). Nonetheless, this proposal suggests that emotional behavior, at least, can be influenced by facial patterning.

This analysis points to the necessity of understanding the social context in which the facial action occurs. Unresolved here are results of conflicting social requests. It would be interesting to see the facial expressions, sub- jective reports, and ANS changes in people asked to display anger, yet be sad. How would role taking influence their responses? What effect would the inner sadness have on the behavior? What effect would the anger dis- play have on the felt sadness?

Multiple Causality

These different proposals should not be viewed as mutually exclusive. The influence of the face on emotions is likely multiply determined. No single proposed mechanism easily accounts for the variety of findings. For example, VTEE does not address asymmetry in brain activity associated

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with certain smiles, but does uniquely predict differences in temperature and breathing associated with affective changes (see Mclntosh et al., in press). Part of the confusion in the literature is probably due to different mechanisms contributing differentially to varying findings. There may be different mechanisms for categorical vs. dimensional effects, for physiologi- cal vs. subjective effects, and for the combinations of these. For example, perhaps only certain highly precise facial patterns activate the CNS mecha- nisms producing categorical physiological effects, yet less exact emotion- analogous configurations cause changes in subjective valence due to breathing-related temperature changes (VTEE). Some mechanisms might be more powerful, or more general than others. Possibly the primary cause varies by emotion, with disgust expressions inducing associated feelings via activation of a central emotions program, and smiles creating positive feel- ings due to classical conditioning, for example. Further investigation into all the proposed mechanisms is necessary, as is careful consideration of which effects are connected with which methods and outcomes. Learning more about the mechanisms of facial feedback will help us to understand emotions processes, point to influences on emotions (including sources of individual differences), and will assist in considering any applications of the effect. However, for some purposes, the specific mechanism is not highly important if the effect is large enough (Capella, 1993; Izard, 1990). Even if the influence of the face is due to classical conditioning or role playing, the effect exists.

IMPLICATIONS OF FACIAL EFFECTS ON EMOTION

Implications for Emotions Theories

Much of the drive in investigating facial feedback comes from those in the Jamesian camp who view it as an integral factor in human emotional processes. The findings regarding correspondence are important here, as they demonstrate that the face is associated with emotion, not just social communication. Indeed, this may be all that is needed for the data to be consistent with some theories (see Tomkins, 1962, 1981).

The evidence in support of the modulation hypothesis is quite impor- tant to several emotions theories, specifically that of Izard (1977, p. 64), in which facial expression can modulate experience only when the expres- sion is "sufficiently veridical." These results thus maintain the plausibility of Izard's theory. The CNS theories also remain plausible, especially as the evidence for the initiation function grows. The work supporting categorical effects is especially important, as these are predicted by these theories. As

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these findings are historically weaker and more controversial, further work should address clearly the existence of categorical effects. As our knowl- edge of neuropsychological processes related to emotions grows, it is likely the CNS theories will be modified. Data from the facial feedback studies are useful in that they might point to neural systems that should be exam- ined for their emotional function. Given recent advances in neuropsy- ehological methods, it is an opportune time to do the empirical work necessary to specify the CNS theories. The ambiguity of ANS specificity may be less relevant if CNS patterns associated with emotions can be iso- lated.

Facial feedback findings are also relevant to a central issue in emotions theories: Is cognition necessary for emotions? Facial feedback may be an example of noncognitive processes influencing emotion, but this depends on one's definition of cognition, and on which mechanisms are responsible for the effect. VTEE may not require cognition. Some conditioning and CNS theories may require only the simplest kind, and then only if cognition is defined to include immediate perceptual knowledge (see Buck, 1980, 1994). The dramaturgical and self-perception routes may need the complex information processing of higher-level cognition. The most recent work (e.g., Mclntosh et al., in press; Schiff & Lamon, 1989, Strack et al., 1988, Zajonc et al., 1989) casts doubt on the necessity of cognitive appraisal. Physical processes appear enough to generate feelings. Just as evidence of more central processes and cognitive and social influences makes a com- pletely peripheral/facial theory of emotion untenable, so the facial feedback data makes a completely cognitive theory less plausible (Berkowitz & Devine, 1995).

Finally, the work in facial feedback is relevant to the question of the existence of basic emotions (see Duclos et al., 1986). Work on the cate- gorical versions of the hypotheses often presumes the existence of basic emotions (e.g., Ekman, 1992). Evidence regarding categorical effects should be taken into account in the discussions about the nature of emotions.

The relevance of these findings for understanding basic processes of emotions notwithstanding, facial effects on emotion are more likely impor- tant the larger their effects are. Matsumoto (1987) reported a small to mod- erate effect size (.343), and both proponents and critics of the hypotheses consider the results as consistent with their views. More affirmative studies have been published since. However, data from modulation studies indicate that the consequences of facial patterning are much smaller than the in- fluence of the stimuli (e.g., Kraut, 1982; Laird, 1974; Lanzetta et al., 1976; Tourangeau & Ellsworth, 1979). "Turning your frown upside-down" may make you feel better than not doing so, but isn't likely to make you feel happy if your new car has just been rear-ended. However, when the context

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is less powerful than a car accident, the initiation function of facial move- ment may play an important role. Once an emotion state is, even weakly, initiated, memories, appraisals, and behaviors may be influenced to be con- sistent with this state, and amplify the original weak state caused by the facial pattern. Below, implications beyond emotion theories are considered.

Implications for Emotion Regulation

Attention toward how individuals regulate or control their emotions has increased recently (see Wegner & Pennebaker, 1993). The ability of voluntary facial action to modulate and initiate emotions indicates that in- dividuals can regulate their emotions by controlling their facial movements. Athletes who "put on a game face" of anger, may increase the aggression with which they perform.

This has both psychological and social applications. Wikan (1989), for example, describes the role of expression as personal and social emotion management in North Bali. There is social pressure to smile during tragedy. Explicit in this practice is the understanding of expressions as causes of inner feelings. If one is socially pressured to smile in the aftermath of trauma, it may decrease the feelings of depression that follow. On the other hand, being coerced to display one emotion while feeling another creates conflict (Hochschild, 1983); facial feedback research may shed light on what occurs in these circumstances. Understanding the individual and social uses of facial feedback to regulate emotions has importance for both everyday emotion regulation and psychotherapy (Gellhorn, 1964; see Izard, 1971, for an extended discussion). This may be one method, for example, for people to begin to alter affective responses to certain circumstances.

Implications for Social Processes

One active area of interest in facial feedback is in research on emo- tional contagion, or socially-induced affect (Hatfield, Cacioppo, & Rapson, 1994; Levenson, in press, Mclntosh, Druckman, & Zajonc, 1994). This is fitting. Strong early evidence for facial feedback came from studies of Lan- zetta and colleagues (e.g., Lanzetta et al., 1976), whose initial work was based in part on research demonstrating socially-induced affect among monkeys (see Mclntosh et al., 1994; McHugo & Smith, this issue). Facial mimicry is one way in which emotions may be socially shared.

The early data led to exploration of the role of the face in the vicarious instigation of affect. Vaughan and Lanzetta (1981) found that participants who amplified their facial responses to the other's pain showed increased

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EDR and HR compared to those who inhibited facial movement, or were given no instructions. Vicarious emotional experience appeared mediated by facial actions of the participant. Combined with the evidence that people mimic the emotional expressions of others, facial feedback provides a mechanism for one person's emotions to influence another's (e.g., Bush et al., 1989; Hatfield et al., 1994; Mclntosh et al., 1994). Forming one's face, either automatically or intentionally, into the same pattern as another per- son's may, via facial feedback, lead to overlap of subjective or physical emo- tional experience. Dyadic rapport is another interpersonal process that may rely in part on facial feedback (Capella, 1993). Mutual mimicry, and resul- tant shared emotions may smooth social interaction. Rapport and empa- t h y - a n d therefore facial feedback--are important for a wide variety of normal social functions (Hatfield et al., 1994; Levenson, in press; Mclntosh et al., 1994).

Difficulties in such processes may be associated with pathology. Early problems in mimicking others may be associated with autism, and may lead to some of the social deficits autistic individuals experience (Rogers & Pen- nington, 1991). Facial feedback is involved in this, as, via mimicry, it could provide the subjective experience of others' emotions that allows normal individuals to develop understandings of others. Neurological problems with the somatic feedback system may be associated with sociopathy (Damasio, 1994).

Finally, social context probably influences facial feedback processes in at least two ways. First, how much individuals express, and what they ex- press is strongly influenced by who they are with (Fridlund, 1994); the facial feedback hypotheses suggest that this will affect the emotions people have in such circumstances. For example, when subjects are being observed dur- ing electric shock, their facial movements, self-reported feelings, and physi- cal arousal are all lower than when alone (Kleck et al., 1976). Second, social cues are another influence on emotions; when they are strong they may outweigh effects of facial feedback.

DIRECTIONS AND QUESTIONS

Research has demonstrated that the face can influence emotions. And, there are a number of potentially important implications of this phenome- non. However, the area is in need of development and refinement. One issue for subsequent work is discerning the circumstances under which the effects are most powerful. First, overall effect size should be reevaluated, adding the recent findings to those used in Matsumoto's (1987) metaana- lysis. In doing this work, the notion of one study, one vote should be

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avoided; certain manipulations, measures, and procedures are more con- vincing than others. Further, an examination of the effects for the different hypotheses would be useful. The power of facial action may vary with in- dividual differences, the facial manipulation used (muscle-by-muscle, ana- log patterns, amplification), varying outcomes (memories, ANS, CNS, subjective experience), and the social context.

Some individual differences have been found relating to sensitivity to internal cues (Laird, 1984). Katkin (1985), for example, has found clear individual differences in the ability to consciously detect heartbeats. People who possess more accurate autonomic self-perception may be more likely to experience facial feedback effects--physical cues may be more powerful for them. A quite consistent finding is that when environmental cues are minimized, men detect physiological changes more readily than women (Katkin, 1985; Pennebaker & Roberts, 1992). This suggests that facial feed- back effects would be more powerful among men than women, especially to the extent self-perception of somatic cues is responsible for the effects. Compatible with this is Wissing and Wessels' (1992) finding that unilateral facial contractions worked only for men.

However, much research finds effects of facial action in mixed-gender samples, and Ohira and Kurono (1993) found effects in a sample of Japa- nese women. Two possibilities are suggested. First, only some mechanisms may be gender related; work should attempt to determine if mechanisms of facial feedback differ across gender. Second, any gender difference may be cultural, and by implication, so might some facial feedback effects (see Pennebaker & Roberts, 1992 for discussion of possible causes of the gender difference). In general, finding individual, gender, and cultural differences in facial feedback and related effects may help untangle the mechanisms responsible for the phenomena. If there are cultural differences, for exam- ple, the mechanisms should be evaluated with respect to how well they can account for these.

Katkin's (1985) work also suggests a situational effect on visceral self- perception. Accuracy of heartbeat detection increases with physically or psychologically-induced arousal. This suggests that in situations of high arousal, somatic feedback effects (including facial) may be enhanced.

One potentially relevant difference in manipulation is whether the fa- cial motion is voluntary or posed. Facial actions are under dual neurological control. Voluntary and involuntary (or, perhaps, constructed vs. over- leamed, see Fridlund, 1994) facial actions involve different neural paths (Matsumoto & Lee, 1993). Izard (1990) claims that this is one reason why studies in which the experimenter manipulates participants' faces show lower effect sizes than those using spontaneous faces. He (Izard, 1981, 1990) suggests that for voluntary facial movements to elicit or regulate emo-

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tion strongly, the movements must be congruent with ongoing cognitive processes.

How different are voluntary and involuntary patterns? Smith, McHugo, and Lanzetta (1986) demonstrated that the pattern of muscle activation in posed happiness, anger, and sadness were highly similar to that generated during imagery of past experiences of the respective emotions; however, during sadness, muscle activity over the brow was more evident in the im- agery task than in the posed expression. Is this difference (and potential ones of similar magnitude) enough to affect facial feedback effects? Some say so. Hager and Ekman (1981) indicate that only faces that very closely match basic emotion patterns will elicit emotions; effects of precision of expression are discussed by Levenson et al. (1990). The differences in in- nervation and muscle action between voluntary and manipulated facial ac- tions may influence the extent of facial feedback. Future work needs to continue to determine the degree differences in facial patterns related to this manipulation, and evaluate whether this difference is significant for facial feedback effects.

One important direction would be to further link facial feedback ef- fects with data on more general somatic feedback effects (see Buck, 1984; Fridlund, 1994). One example of this is Duclos et al. (1989), who examined both facial and posture feedback. Another is Schiff and Lamon (1994), who extended their work on unilateral facial contractions to squeezing a ball in either the right or left hand. Their findings were parallel with those of the facial contraction studies reported above. Most of the proposed mecha- nisms for facial feedback are relevant to postural, and perhaps vocal feed- back effects, for instance (Hatfield et al., 1994). For example, can breathing as one does while angry cause feelings of anger by activating the emotions program also initiated by an angry facial pattern? Expanding the research more completely to the body will provide information on both the mecha- nism and the power of facial feedback effects.

CONCLUSION

Recent evidence bolsters previous work demonstrating that facial ac- tion corresponds to emotions, and can modulate and initiate emotional ex- perience. There is still no evidence that facial action is necessary for emotions. Evidence for categorical effects has grown. Support for the phe- nomena is not always obtained, however. This is likely due to causes of facial movement beyond emotional state (e.g., communicative intent), and to influences on emotion in addition to facial feedback (e.g., cognitive ap- praisal). Further, a lack of knowledge regarding the parameters of feedback

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processes makes finding the effect more difficult. Future work may isolate a more constrained process that is more reliable.

A focus on determining the contribution of various mechanisms to fa- cial feedback effects is necessary. Knowledge of h o w facial actions influence emotions will advance understanding of emotions processes in general, and will clarify the role of the face in emotional and social domains. Such in- formation will also assist in defining the parameters within which feedback effects occur. Determining mediators and moderators of facial feedback will provide a more solid foundation on which to examine both basic ques- tions and applications of this phenomenon.

Even if the Jamesian mechanisms (i.e., those that include facial feed- back as integral to emotional processes) are not supported, the existence of facial feedback effects has significant implications. Facial influence on emotions may play a particularly important role in an array of intrapersonal and interpersonal dynamics (e.g., emotion regulation and socially-induced affect). Research on these applications of facial feedback effects should proceed in parallel to development of investigation of the basic phenomena.

A quarter-century of rapidly expanding research has laid the ground- work for exploring complex and difficult questions about facial feedback processes. To progress, the field must move past replication of demonstra- tions of such phenomena to focused work on discerning their mechanisms, parameters, and applications. This work has started, with several programs of research now addressing some of these points. There is much more to be done; the next 25 years should be an exciting time to investigate this element of emotional and social processes.

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