- Email: [email protected]
Do Unilateral Right and Left Face Contractions Induce Positive and Negative Emotions? A Further Test of Schiff and Lamon's (1989) Hypothesis
Brain and Cognition 47, 513–524 (2001) doi:10.1006/brcg.2001.1329, available online at http://www.idealibrary.com on
Do Unilateral Right and Left Face Contractions Induce Positive and Negative Emotions? A Further Test of Schiff and Lamon’s (1989) Hypothesis Travis G. Fogel School of Medicine, University of California, Los Angeles
and Lauren Julius Harris Michigan State University Published online November 16, 2001
Schiff and Lamon (1989) proposed that unilateral face contractions induce positive or negative changes in emotion depending on the side of contraction; support for this proposal, however, has been mixed. In a new test, 40 right-handed and 38 left-handed men performed four alternating face contractions (LRLR or RLRL) and, after each one, completed a different version of the Depression Adjective Checklist (Lubin, 1994). A repeated-measures ANCOVA failed to reveal any significant effect of side of face contraction or handedness on direction of emotion change. Instead, regardless of side of contraction, the subjects’ negative emotional state increased significantly across the four contractions with the degree of change being significantly related to the subjects’ reported level of difficulty in holding the contraction irrespective of whether the more difficult side was the left or the right. 2001 Elsevier Science Key Words: laterality; face contraction; emotion; valence hypothesis; handedness.
The so-called ‘‘valence hypothesis’’ for cerebral organization of emotion posits that the left and right hemispheres are specialized for the experience of positive and negative emotions, respectively, where positive emotions include cheer, elation, and confidence and negative emotions include sadness, grouchiness, and distress (Silberman & Weingartner, 1986). Support for the hypothesis has been mixed. Evidence for it has come from research on clinical and normal populations, including studies of emotional displays in persons with unilateral cerebral lesions (Sackeim et al., 1982) and in persons with epilepsy who undergo the Intracarotid Amobarbital Procedure (Ross & Rosadini, 1967) and studies of asymmetries in cortical activity in persons induced into emotional states (Davidson, Schwartz, Saron, Bennet, & Goldman, 1979) and in persons with clinical depression (Henriques & Davidson, 1991). Evidence against the hypothesis has come from research on similar clinical and normal Some of the data in this report were presented at the poster session of the 9th annual meeting of TENNET, Montreal, Canada (June, 1998). Address correspondence and reprint requests to Lauren Julius Harris, Department of Psychology, Michigan State University, Psychology Research Building, East Lansing, MI 48824. Fax: (517) 3531652. E-mail: [email protected]. 513 0278-2626/01 $35.00 2001 Elsevier Science All rights reserved.
514
FOGEL AND HARRIS
populations, including studies finding that, irrespective of valence, emotional disturbances are more common following right- than left-hemisphere injury (Lishman, 1968), that emotional changes in persons with temporal lobe epilepsy are more common in those with right- than with left-sided foci (Bear & Fedio, 1977), and that emotional responses in normal persons are stronger to happy and sad films alike when presented to the right than to the left hemisphere (Wittling & Roschmann, 1993). Over the past decade Schiff and Lamon and their colleagues have reported further support for the valence hypothesis with a new method—unilateral contractions of the lower muscles of the face. With college students as subjects and using a variety of dependent measures—response to an open-ended instruction to attend to and report on their emotional experiences (Schiff & Lamon, 1989), responses to TAT cards (Schiff & Lamon, 1989), and response to instructions to describe different ethnic groups (Schiff, Esses, & Lamon, 1992)—left-side contractions were found to produce more negative changes, right-side contractions more positive changes in emotional state.1 For left-side contractions, the effects in one experiment were dramatic, at one point producing weeping in 3 of 12 subjects (Experiment 1 in Schiff & Lamon, 1989). The same general lateralized effects also were found for men and women alike. Finally, the effects are not restricted to face contractions: The same effects have been reported for unilateral contractions of the muscles of the hand, as indexed by responses to TAT cards (Schiff & Lamon, 1994), judgments of the emotional valence of chimeric faces (Schiff & Truchon, 1993), and persistence in trying to solve unsolvable problems (Schiff, Guirguis, Kenwood, & Herman, 1998). Schiff and Lamon (1993) cite their ability to produce the valence effect under a number of different conditions as a sign of the method’s being ‘‘quite robust’’ (p. 551). To explain the effects of the contraction method, Schiff and Lamon (1989) propose a two-step mechanism: first, inasmuch as the muscles of the lower two-thirds of the face as well as the muscles of the hand are innervated predominantly by the contralateral hemisphere, unilateral contraction of these muscles is assumed to predominantly activate sensory and/or motor areas in the contralateral hemisphere; second, on the assumption that neural activation spreads to nearby cortical and limbic regions, including regions that mediate emotional states, there is arousal of the emotional state—positive or negative—primarily associated (according to the valence hypothesis) with that hemisphere. If the contraction method works as Schiff and Lamon (1989) suppose, it would provide an important new way to test the valence hypothesis in clinical as well as nonclinical populations. The main reason is that it would allow for the selective (or predominant) activation of each hemisphere while avoiding, according to Schiff and Lamon, the intervening cognitions and demand characteristics associated with more conventional emotion-induction methods, such as the use of narratives, self-statements, films, or music (for reviews, see Gerrards-Hesse, Spies, & Hess, 1994; Martin, 1990; Westermann, Spies, Stahl, & Hesse, 1996). Other than the studies by Schiff and Lamon and their colleagues, however, the method has found mixed support in the two tests that we know to have been performed in other laboratories, by Kop, Merckelbach, and Muris (1991), and by Wissing and Wessels (1992). Kop et al. (1991) failed to replicate the effect altogether and, instead, found only 1 In describing their results, Schiff and Lamon (1989) use the terms ‘‘emotional state’’ and ‘‘mood’’ interchangeably. Other researchers, however, use them differently. For example, according to Ekman (1994) and Davidson (1994), emotions are brief ‘‘phasic perturbations,’’ have a specific focus, and serve to modulate or bias action, whereas moods are longer lasting, have a more generalized focus, and serve to bias cognition. By this usage, the face-contraction method would seem to be better described as a method of emotion-induction than as a method of mood induction. In the current article, we shall use the term ‘‘emotional state’’ to avoid any misinterpretation.
FACE CONTRACTIONS AND EMOTION
515
an interaction between side of face contraction and contraction sequence such that, irrespective of side of contraction, contractions performed later in the sequence produced more negative reactions than those performed earlier in the sequence. This led Kop et al. (1991) to conclude that the operative factor was fatigue—that subjects grew more fatigued as they proceeded through the contraction sequence and that this is what was reflected in their increasingly negative reaction over this period. At the end of their experiment, Kop et al. (1991) asked their subjects which of the contractions, the left- or the right-sided, were the more difficult to maintain. The results showed that, although the emotional changes did not vary with side of contraction, they did vary according to the side that the subjects said was more difficult to maintain, with more negative reactions following contraction of the more difficult side. For some subjects, the more difficult side was the right, and for a nearly equal number of others, it was the left. In a commentary, Schiff and Lamon (1993) pointed to two features of Kop et al.’s (1991) procedure that could have interfered with their subjects’ awareness of changes in their emotional state as well as with their ability to report on these changes. The first was in the contraction sequence. Whereas Schiff and Lamon (1989) used straight alternation (LRLR or RLRL), Kop et al. used a massed-trial procedure (three sameside contractions before alternation, LLLRRR or RRRLLL). Schiff and Lamon (1993) suggested that straight alternation, with subjects reporting after each contraction, better allows subjects to compare differences between sides, thereby enhancing the saliency of their emotional experiences and facilitating their awareness of them (see also Schiff et al., 1998). They based this supposition on data (Schiff, Esses, & Lamon, 1992) indicating that straight alternation produced more frequent and reliable changes in emotional states than did massed trials. The second feature was the dependent measure. Kop et al. (1991) had their subjects do two things: evaluate the favorableness of a human cartoon face after each one of the total of six contractions and also report on their own emotional state after the third contraction of each set of the three consecutive left- or right-side contractions. Schiff and Lamon (1993) speculated that the subjects’ self-reports of emotional states following the three consecutive contractions may have been affected by the prior evaluations of the cartoon drawings made after each contraction, that is, that the subjects’ emotional state may have been influenced by their cartoon evaluations as well as by their face contractions. In their reply, Kop et al. (1993) pointed to what they regarded as shortcomings in Schiff and Lamon’s (1989) own experimental procedure and therefore concluded that, in light of their own evidence on difficulty of contraction, ‘‘it remains to be seen whether unilateral contraction effects reported by Schiff and Lamon need a neuropsychological explanation’’ (p. 554). If Schiff and Lamon’s (1993) criticisms are reasonable, they are, in any case, vitiated by the study by Wissing and Wessels (1992). The reason is that when Wissing and Wessels used Kop et al.’s (1991) massed-trial procedure, they found the valence effect only when they had their subjects, after each face contraction, point to the one face on a card displaying photographs of 10 faces whose emotional expression most clearly matched their own emotional state during the contraction (5 faces showed positive expressions and 5 showed negative expressions), and even under this condition, the valence effect was shown only by men, not women. When, however, Wissing and Wessels had their subjects make open-ended reports of their emotional state after each contraction similar to the kind of reports relied on by Schiff and Lamon (1989), no valence effect was found. Instead, for both sexes, negative reports predominated, irrespective of side of contraction, just as Kop et al. (1991) had found. Unlike Kop et al. (1991), however, Wissing and Wessels did not ask their subjects to report on
516
FOGEL AND HARRIS
the difficulty of contraction, which means that they could not assess its relation to their subjects’ emotional states. Furthermore, even though they collected self-reports of emotional state after each contraction, their analyses included only the sum total of reports after left- and right-side contractions, which means that they could not assess possible effects of order of contraction or of fatigue on emotional state. Finally, unlike Schiff and Lamon (1989), Wissing and Wessels failed to include any precontraction measure of emotional state, which means that they could not take into account the possible relation between initial emotional state and subsequent changes in that state. Our goal in the current study was to further examine Schiff and Lamon’s (1989) hypothesis using the same face-contraction sequence as they used as well as the same method of producing the contraction. In this way, we hoped to avoid the difficulties in interpretation that faced Kop et al. (1991) in their failed replication. The only difference was in the dependent measures. In place of the TAT and the open-ended report of emotional state used by Schiff and Lamon (1989), we measured self-report of emotional state after each contraction on a standardized adjective check list with several parallel forms. This allowed us to quantify the degree of change in emotional state across contractions. Like Schiff and Lamon (1989), we also administered the check list prior to the first contraction in order to control statistically for initial emotional state. Finally, for 62 of the 78 subjects, we included a difficulty-of-contraction measure so that we could assess any possible relation between emotional state changes and the relative difficulty of holding each side of the face in the contracted position.2 Given that Schiff and Lamon (1989) found the effect in both sexes, whereas Wissing and Wessels (1992) found it only in men, we confined our study to men to maximize the likelihood of finding an effect. Finally, in all of the studies by Schiff and colleagues, as well as in the studies by Kop et al. (1991) and Wissing and Wessels (1992), only right-handers were tested. We expanded our sample to include lefthanders. We did this for two reasons. First, because left-handers are reported to differ from right-handers on select psychological tasks and to be more common in certain clinical and other special populations (e.g., Harburg, Roeper, Ozgoren, & Feldstein, 1981; Hicks & Pelligrini, 1978; see review in Harris, 1992), we were curious to see whether left- and right-handers also would differ in overall frequency and intensity of negative and positive emotions after face contraction. Prior studies of handedness and the experience of emotion are of uncertain guidance here, with left-handers sometimes showing asymmetries similar in size and direction to those shown by righthanders (e.g., Robinson, Lipsey, Bolla-Wilson, et al., 1985), other times smaller but in the same direction (e.g., Smith, Kline, & Meyers, 1990), and still other times in the reverse direction (e.g., McFarland & Kennison, 1989). The face-contraction method, and its claimed ability to bypass intervening cognitions common to conventional induction methods, thus may prove useful for comparing the neuropsychological organization of emotion in left- and right-handers. Second, left-handers and righthanders reportedly differ in the side of the face they find more ‘‘convenient’’ to move when asked to perform facial exercises, including lateral movements of the angle of the mouth, winking, platysma contraction, raising and everting the upper lip with dilation of the nostril, and vertical wrinkling of the forehead, with right-side movements more ‘‘convenient’’ for right-handers and left-side movements more ‘‘conve2
Although we already knew of Kop et al.’s (1993) finding, this question had not been part of our original design. We added it to the protocol only after several subjects among the first 16 tested reported spontaneously that one side of the face was harder to hold in the contracted position than the other side. Only then did we realize the potential importance of Kop et al.’s finding.
FACE CONTRACTIONS AND EMOTION
517
nient’’ for left-handers (Chaurasia & Goswami, 1975). Assuming that the authors’ term ‘‘convenient’’ refers to level of difficulty, the results suggests the possibility of a relation between handedness, side of greater difficulty in performing the face contraction, and the direction and degree of change in emotional state. In sum, if Schiff and Lamon’s (1989) face-contraction method works as they suppose, and if the valence hypothesis is correct, then negative emotional state should increase following left-side contractions and should decrease following right-side contractions. The outcome in left-handers is harder to predict for reasons noted above. At the least, any emotional state changes in left-handers might be expected to be smaller or more variable than those in right-handers. METHOD
Subjects The subjects were 78 undergraduate college men (49 right-handed and 38 left-handed, mean age ⫽ 20.1 years). All were volunteers from introductory psychology courses who participated for course credit, and all were tested following protocols approved by the Michigan State University Committee on Research Involving Human Subjects. On a medical screening questionnaire, none of the subjects reported current or past brain damage, paralysis, injury, muscle weakness, clinical depression, or any other conditions that could be possible sources of confounding. Subjects were randomly assigned to either the LRLR or RLRL contraction-order condition with the constraint that each condition included an equal number of right- and left-handers. Handedness was assessed on an eight-item modified version of the Edinburgh Handedness Inventory (Oldfield, 1979).
Face Contraction Schiff and Lamon’s (1989) instructions for producing the unilateral face contractions were followed as closely as possible. The experimenter (T.G.F.), facing the subject, began by explaining how the subject was to perform the facial manipulation. The experimenter said, ‘‘I want you to pull back and raise the [left/right] side of your mouth as much as you can, just like this.’’ The instruction named the left side for subjects in the LRLR condition and the right side in the RLRL condition, and, for each condition, the experimenter demonstrated by making the movement himself. The experimenter then said, ‘‘Now you try it.’’ After the subject successfully made the required movement, the experimenter said, ‘‘That’s fine. When the experiment starts, I want you to hold it in that position for forty-five seconds until I say relax.’’ The subject also was told to breathe normally during the contraction, to maintain eye contact with the experimenter, and to pay close attention to his emotions, to ‘‘how you are feeling,’’ rather than to his thoughts or facial sensory experiences. The intention behind this last instruction was to minimize the subject’s focus on peripheral/physical sensations during the contraction, such as the difficulty of holding the position, which, as already noted, Kop et al. (1991) found could affect emotional state. If necessary, further instructions were given until both the subject and experimenter agreed that the subject understood how to perform the contraction. Further instructions were needed for seven subjects, all of whom showed too small a contraction on their first attempt. All succeeded on a second attempt. In each contraction-order condition, LRLR or RLRL, subjects completed a series of four contractions, each lasting 45 s, with the side of contraction alternating each time. After each contraction, subjects were instructed to relax and to complete a different version of a short check list designed to measure their emotional state.
Test Materials Depression Adjective Check List (DACL). Because we wanted to assess changes in emotional states after each contraction, the instrument we chose was one that could be administered quickly and repeatedly, the Depression Adjective Check List, or DACL (Lubin, 1981, 1994). The DACL is a multipleitem paper-and-pencil check list designed to measure transient emotional states. It has well-established norms and high test–retest reliability in college students (Lubin, Van Whitlock, Swearngin, & Seever, 1993), can be administered quickly (1–2 min), and has several parallel forms designed for use in research, in particular for research using repeated measures. It also has been frequently used to measure changes in emotional state, and its sensitivity to such changes is well documented (e.g., Lubin, Swearngin, &
518
FOGEL AND HARRIS
Seaton, 1992; Lubin & Van Whitlock, 1993; Lubin, Van Whitlock, Swearngin, & Seever, 1993; Lubin, Van Whitlock, McCollum, et al., 1994). The different parallel forms are A, B, C, and D, each with 22 negative adjectives and 10 positive adjectives, and Form G, with 22 negative adjectives and 12 positive adjectives. The different forms are highly intercorrelated (.85–.92; Lubin, 1994), and a factor analysis reveals two factors: depressive affect and positive affect (Van Whitlock, Lubin, & Noble, 1995). The manual provides conversion tables and scoring forms for each test form for both T scores and percentile scores for state-negative moods, state-positive moods, and state mood total. The state mood total is calculated as the sum of positive adjectives endorsed (i.e., state-negative mood) and the number of positive adjectives not endorsed (i.e., 10 minus the state-positive mood for DACL A, B, C, and D, and 12 minus the state-positive mood for DACL-G) or State-Total ⫽ 10 ⫺ State Positive ⫹ State Negative). For purposes of this study, only the state mood total T scores were used in any statistical analyses using the DACL. Difficulty-of-contraction question. To measure self-reported difficulty of holding each side of the face in the contracted position, subjects were asked, at the end of the experiment, which contraction— left or right—was more difficult to hold and to record their answer on a 9-point scale, ranging from 1 (Left Side More Difficult) to 9 (Right Side More Difficult), with 5 (Same Difficulty) as a midpoint.
Procedure Subjects were tested individually in a small, quiet room with only the experimenter present. Subjects first provided written consent and completed the handedness measure and the first of the five different forms of the DACL. After becoming familiar with the procedure for performing the contraction, subjects completed the series of four contractions (45 s each). After each one, they completed another of the remaining forms of the DACL. At the end of the experiment, they were asked the difficulty-of-contraction question.
Design A 2 ⫻ 2 ⫻ 4 mixed design was used, with handedness (left or right) and contraction-order condition (LRLR or RLRL) as between-subjects variables and with sequence position (first, second, third, or fourth contraction) as the within-subjects variable. With this design, the test of the valence hypothesis comes not from comparison of the contraction-order conditions but from the assessment of the interaction between contraction-order condition and sequence position.
RESULTS
Side of Contraction DACL T scores were first calculated using the conversion tables for the DACL state mood total (Lubin, 1994). The results are summarized in Table 1 and show the mean DACL T scores after left and right contractions for each handedness group in each contraction condition. A 2 ⫻ 2 ⫻ 4 repeated-measures analysis of covariance (ANCOVA) was performed on the DACL T scores, with emotional state prior to first contraction as a covariate. The results failed to show a significant main effect for contraction-order condition, F(1, 73) ⫽ 1.05, p ⫽ .31, or for the interaction of contraction order by sequence position, F(3, 219) ⫽ 2.43, p ⫽ .07, indicating that side of contraction and DACL scores were unrelated. With one exception, all other main effects and interactions were also nonsignificant [handedness, F(1, 73) ⫽ 2.80, p ⫽ .10; handedness ⫻ sequence position, F(3, 219) ⬍ 1; handedness ⫻ side of contraction ⫻ sequence position, F(3, 219) ⫽ 2.29, p ⫽ .08]. The exception was for position of the contraction in the sequence, F(3, 219) ⫽ 8.52, p ⬍ .001. The results showed that DACL scores increased significantly across the sequence of four contractions, indicating that the subjects’ emotional state grew worse, or more negative, over this period.
519
FACE CONTRACTIONS AND EMOTION
TABLE 1 Effects of Handedness, Contraction Condition, Sequence Position on Mean DACL T Scores Sequence Contraction order
Precontraction DACL-A
1 DACL-B
2 DACL-C
3 DACL-D
4 DACL-G
RLRL Total Group (n ⫽ 38) Right-Handers (n ⫽ 19) Left-Handers (n ⫽ 19)
46.1 (22.0) 45.6 (23.7) 46.5 (19.0)
R 53.4 (22.1) 55.0 (23.5) 51.9 (21.1)
L 55.0 (20.8) 64.3 (17.0) 45.6 (20.5)
R 62.6 (20.0) 66.9 (20.3) 58.2 (19.1)
L 68.0 (20.0) 71.2 (22.8) 64.7 (16.7)
LRLR Total Group (n ⫽ 40) Right-Handers (n ⫽ 21) Left-Handers (n ⫽ 19)
39.2 (20.6) 39.8 (22.2) 38.5 (19.3)
L 52.0 (24.1) 54.1 (27.5) 49.6 (20.2)
R 63.8 (21.6) 62.2 (24.7) 65.5 (18.3)
L 60.2 (22.7) 61.7 (24.5) 58.4 (21.0)
R 65.0 (22.5) 67.1 (22.2) 62.7 (23.2)
Note. Standard deviations are in parentheses.
Difficulty-of-Contraction Effects To determine whether subjects’ self-reported difficulty in performing the left- and right-side contractions was related to their changes in emotional state (DACL scores), subjects were grouped into left- or right-face groups based on their response to the 9-point scale question. As noted above, only 62 of the 78 subjects made this selfrating, and of this number, 26 (41.9%) indicated that left-side contractions were more difficult, 31 (50%) indicated that right-side contractions were more difficult, χ 2(1, N ⫽ 57) ⫽ p ⫽ .439, and 5 (8.1%) indicated that both were equally difficult. Of the 26 subjects for whom left-side contractions were more difficult, 17 (65.3%) came from the RLRL group; in contrast, of the 31 subjects for whom right-side contractions were more difficult, 21 (67.7%) came from the LRLR group, χ 2 (1, N ⫽ 57) ⫽ p ⬍ .05. Thus, order of sequence and face-contraction difficulty were related, with the subjects in the RLRL condition more likely to judge the left contractions as more difficult, and the subjects in the LRLR condition more likely to judge the right contractions as more difficult. Contrary to prior evidence (Chaurasia & Goswami, 1975), handedness proved to be unrelated to side of greater difficulty, χ 2 (1, N ⫽ 57) ⫽ p ⫽ .57. To test the relation between difficulty of contraction and emotional state in the two handedness groups, a 2 (left vs right more difficult) ⫻ 2 (side of contraction) ⫻ 2 (left- or right-handed) ANOVA was performed on the DACL T scores. The analysis failed to show significant main effects for difficulty of contraction, F(1, 53) ⬍ 1, side, F(1, 53) ⬍ 1, or handedness F(1, 53) ⫽ 2.23, p ⫽ .14. All interactions were nonsignificant except for the one between difficulty of contraction and side of contraction, F(1, 53) ⫽ 9.11, p ⬍. 01. That is, subjects who reported that left contractions were more difficult also reported experiencing more negative emotional states (higher DACL scores) after left than after right contractions. Likewise, subjects who reported that right contractions were more difficult reported experiencing more negative emotional states after right than after left contractions (see Table 2).
520
FOGEL AND HARRIS
TABLE 2 Reported Contraction Difficulty and Side of Contraction on DACL T Scores Side of contraction Contraction difficulty
Left
Right
Left Side More Difficult (n ⫽ 26) Right Side More Difficult (n ⫽ 31)
130.2 (45.7) 108.2 (41.0)
115.7 (42.0) 119.7 (41.1)
Note. DACL T scores for side of contraction reflect the sum of the two left-sided contractions and the sum of the two rightsided contractions.
DISCUSSION
Despite our close adherence to Schiff and Lamon’s (1989) procedure for producing the face contractions, we found no evidence that, in normal persons, positive and negative emotional changes are related to side of contraction, and thus we found no support for the valence hypothesis using this method. The results instead showed a significant increase in negative emotional state over time, regardless of side of contraction, and a significant relation between the reported difficulty in holding the contraction and the degree of negative emotional state. With respect to the valence hypothesis, we can think of at least four possible reasons for our null results. First, Schiff and Lamon (1989) reported that in one of their studies, changes in emotional states did not appear until the third and fourth contractions. Our null effects, therefore, may have resulted from our having used DACL scores from all four contractions in our analyses. To check this possibility, we reexamined the data using only the last two contractions in the RLRL condition and the last two in the LRLR condition. The results were unchanged. That is, all main effects and interactions were nonsignificant except for position of contraction in the sequence. In other words, the new analysis showed that emotional state was more negative after the last, or fourth contraction, whether L or R, than after the third contraction. The second possibility is that the DACL, despite its wide and successful use as a measure of changes in emotional state, is insufficiently sensitive to the emotional changes induced by unilateral face contraction. But this seems unlikely, given that the DACL did disclose the overall change in our subjects’ emotional states from precontraction to the fourth contraction, with the average change exceeding 1 standard deviation (see Table 1). It therefore seems highly likely that it would have been sensitive as well to the weeping that, as noted above, Schiff and Lamon (1989) observed in one of their first experiments, although none of our 78 subjects showed any such reaction. That the DACL was sufficiently sensitive also is indicated by the demonstrated relation between our subjects’ DACL scores and their self-reported difficulty of holding the contraction. The third possibility is that our having included all DACL scores in the analyses washed out any effect that existed in the first place. In Schiff and Lamon’s (1989) second experiment, which measured self-report after each face contraction, only 22 of 30 subjects produced any ‘‘classifiable’’ responses at all (i.e., reports of negative, positive, or neutral emotional state), and of the total of 120 responses made by these 22 subjects, only 56 responses (46.7%) could be classified as having followed left
FACE CONTRACTIONS AND EMOTION
521
or right contractions. The other responses could not be classified. If, as these figures suggest, emotional states are reported relatively infrequently, occurring less than half the time, it raises the possibility that even though our dependent measure yielded quantitative scores, our use of all reports of emotional state from all contractions on all subjects somehow obfuscated any changes like those found by Schiff and Lamon (1989). Wissing and Wessels (1992), however, used all responses in their analyses, and theirs, as noted above, was the only successful, or rather partially successful, replication to date other than those by Schiff, Lamon, and colleagues themselves. Nevertheless, to check this possibility, we reexamined our data for only those subjects reporting changes in emotional states that were significantly different from their precontraction levels. We defined such individuals by two separate methods and performed two separate statistical analyses for each method—an ANCOVA using all four contractions in the sequence and an ANCOVA using only the last two contractions. For the first method, we selected subjects who showed at least a 1 standard deviation change in DACL scores from precontraction to the fourth and final contraction in the sequence, where the standard deviation was determined using the total sample standard deviation of precontraction scores. By this method, 39 (50%) subjects met criterion, similar to the percentage of ‘‘classifiable responses’’ reported by Schiff and Lamon (1989). Reexamination of the data using this method, however, did not change the results: for four contractions, F(3, 120) ⫽ 1.38, p ⫽ .251; for the last two contractions, F(3, 40) ⬍ 1. For the second method, we selected the top 25% of subjects who produced the largest changes in emotional state from precontraction to fourth contraction. Again, the results were unchanged: for four contractions, F(3, 54) ⫽ 1.30, p ⫽ .284; for the last two contractions, F(1, 17) ⬍ 1. Regardless, then, of the method of analysis or subject selection, the results remained unchanged. The fourth possibility is that the difficulty of holding the contraction had a more salient effect on emotional state than did any changes associated with side of contraction per the valence hypothesis. Like Kop et al. (1991), we found an association between negative emotional state and the reported difficulty of holding the contraction, and, also like Kop et al., we found that approximately the same number of subjects rated the left-side contractions as more difficult as rated the right-side contractions as more difficult. These results, along with our finding that subjects’ negative emotional state increased across the sequence of contractions, suggest that the DACL scores reflect the fatigue of holding the contraction. They, therefore, also suggest that our subjects’ emotional states were linked to their physical sensations even though we instructed them to focus on their emotions. In this connection, it is noteworthy that Schiff and Lamon (1989) reported that their subjects’ ‘‘unclassifiable’’ responses included reports of facial sensory experiences. If, therefore, the valence hypothesis is correct and if the face-contraction method is a valid way to induce emotional states, it suggests that any cerebrally mediated differences in emotional state induced by face contraction may have been overpowered by attention to the physical difficulty of the contraction. This possibility is supported by a recent study by Williams, Lees-Haley, and Price (1998). In an ‘‘undivided self-attention’’ condition, one group of normal adults was instructed to attend to their thoughts, feelings, and sensations and to report any physical symptoms and emotional symptoms related to anxiety and depression on a measure of physical complaints and disposition to report symptoms (Pennepacker Inventory of Limbid Languidness; Pennepacker, 1982) and on a measure of mood, or affective states (Profile of Mood States; McNain, Lorr, & Droppleman, 1981). In a ‘‘self-distraction’’ condition, another group was asked to keep a mental tally of the number of items in the inventory related to physical versus emotional symptoms. The result was that physical symptoms and reports of anxiety and depression were greater after self-attention instructions than after self-
522
FOGEL AND HARRIS
distraction instructions. If we were to liken our subjects to Williams et al.’s selfattention group, it would suggest that our subjects’ increases in negative emotional states across contractions may have been due, in large measure, to self-attention to internal states. Preliminary support for this suggestion comes from a recent study conducted in our laboratory in which one group of normal adults (face group) performed four unilateral face contractions and another group (face-hand group) performed four unilateral face contractions while simultaneously making contractions of the hand on the same side. On the DACL, administered following the fourth contraction, the face group reported increases in negative emotional states regardless of side of contraction, just as we found in the current study, whereas the face-hand group showed no significant changes in emotional state. This suggests that in the face-hand group, the hand contraction may have diminished the subjects’ attention to the sensation of the face contraction, similar to the distraction condition in the Williams et al. (1998) study.
SUMMARY
Although all of these possibilities deserve consideration, our null results, in the end, provide no support for Schiff and Lamon’s (1989) conclusions pertaining to the effects of the face-contraction method. It is difficult to say what this means in terms of the valence hypothesis for the experience of emotion. For instance, the absence of differences between contraction side and emotional state may cast doubt on the valence hypothesis for the experience of emotion, or it may simply mean that we failed to find any difference for one or more of the reasons discussed above. Likewise, our null results for handedness could mean that the neuropsychological organization for the experience of emotion is the same in right- and left-handers, consistent with certain other studies, or that differences do not appear for some of the same reasons already discussed. In summary, our results, like those of Kop et al. (1991), question the proposition that left- and right-side face (or hand) contractions produce different changes in emotional state. Schiff and Lamon (1993) cite their ability to produce the valence effect with different measures under different conditions as a sign of their method’s ‘‘robustness,’’ but a robust method ought to yield reproducible effects in other laboratories. To date, the face-contraction method has not met this criterion. We therefore suggest that before it can be accepted as a method for testing the valence hypothesis, it needs further study. In particular, dependent measures must be developed that are maximally sensitive to the effects of the face contractions while also controlling for the effects of the physical effort of making and holding the contractions. Until then, we concur with Kop et al.’s (1993) conclusion that ‘‘it remains to be seen whether the unilateral contraction effects reported by Schiff and Lamon need a neuropsychological interpretation’’ (p. 554). In other words, we cannot rule out the possibility that the effects represent only the action of peripheral, or muscular, cues.
REFERENCES Bear, D. M., & Fedio, P. (1977). Quantitative analysis of interictal behavior in temporal lobe epilepsy. Archives of Neurology, 34, 454–467. Borod, J. C., Caron, H. S., & Koff, E. (1987). Asymmetry of facial expression related to handedness, footedness, and eyedness: A quantitative study. Cortex, 17, 381–390.
FACE CONTRACTIONS AND EMOTION
523
Bulman-Fleming, M. B., & Bryden, M. P. (1994). Simultaneous verbal and affective laterality effects. Neuropsychologia, 32, 787–797. Chaurasia, B. D., & Goswami, H. K. (1975). Functional asymmetry in the face. Acta Anatomica, 91, 154–160. Davidson, R. J. (1994). On emotion, mood, and related affective constructions. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion: Fundamental questions (pp. 51–55). New York: Oxford Univ. Press. Davidson, R. J., Schwartz, G. E., Saron, C., Bennett, J., & Goldman, D. J. (1979). Frontal vs. parietal EEG asymmetry during positive and negative affect. Psychophysiology, 16, 202–203. [Abstract] Ekman, P. (1994). Moods, emotions, and traits. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion: Fundamental questions (pp. 56–58). New York: Oxford Univ. Press. Gerrards-Hesse, A., Spies, K., & Hesse, F. W. (1994). Experimental inductions of emotional states and their effectiveness: A review. British Journal of Psychology, 85, 55–78. Harburg, E., Roeper, P., Ozgoren, F., & Feldstein, A. M. (1981). Handedness and temperament. Perceptual and Motor Skills, 52, 283–290. Harris, L. J. (1992) Left-handedness. In I. Rapin & S. J. Segalowitz (Eds.), Handbook of neuropsychology: Child neuropsychology (Vol. 6, pp. 145–208). Amsterdam: Elsevier. Henriques, J. B., & Davidson, R. J. (1991). Left frontal hypoactivation in depression. Journal of Abnormal Psychology, 100, 535–545. Hicks, J. B., & Pelligrini, R. J. (1978). Handedness and anxiety. Cortex, 14, 119–121. Kop, W. J., Merckelbach, H., & Muris, P. (1991). Unilateral contraction of facial muscles and emotion: A failed replication. Cortex, 27, 101–104. Kop, W. J., Merckelbach, H., & Muris, P. (1993). Unilateral contraction and induction of emotion: A reply to Schiff and Lamon. Cortex, 29, 553–554. Lishman, W. A. (1968). Brain injury in relation to psychiatric disability after head injury. British Journal of Psychiatry, 114, 373–410. Lubin, B. (1981). The State Trait Depression Adjective Check Lists. San Diego, CA: Educational and Industrial Testing Services. Lubin, B. (1994). The State Trait-Depression Adjective Check Lists Manual. Odessa, FL: Psychological Assessment Resources. Lubin, B., Swearngin, S. E., & Seaton, K. (1992). Research with the Depression Adjective Check Lists, 1965–1991. Odessa, FL: Psychological Assessment Resources. Lubin, B., & Van Whitlock, R. (1993). Diagnostic efficiency of the Depression Adjective Check Lists. Journal of Clinical Psychology, 49, 695–701. Lubin, Van Whitlock, R., McCollum, K. L., Thummel, H., Denman, N., & Powers, M. (1994). Measuring the short-term mood of adolescents: Reliability and validity of the state form of the Depression Adjective Check Lists. Adolescence, 29, 591–604. Lubin, B., Van Whitlock, R., Swearngin, S. E., & Seever, M. (1993). Self-assessment of state and trait depressive affect by college students: Reliability and validity of an adjective check list. Journal of College Students Development, 34, 249–255. Martin, M. (1990). On the induction of mood. Clinical Psychology Review, 10, 669–697. McFarland, R. A., & Kennison, R. (1989). Handedness affects emotions valence asymmetry. Perceptual and Motor Skills, 68, 435–441. McNair, D. M., Lorr, M., & Droppleman, L. F. (1981). Profile of Mood States Manual. San Diego, CA: Educational and Industrial Testing Service. Oldfield, R. C. (1979). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97–113. Pennepacker, J. W. (1982). The psychology of physical symptoms. New York: Springer-Verlag. Robinson, R. G., Lipsey, J. R., Bolla-Wilson, K., Bolduc, P. L., Pearlson, G. D., Rao, K., & Price, T. R. (1985). Mood disorders in left-handed stroke patients. American Journal of Psychiatry, 142, 1424–1429. Ross, G. F., & Rosadini, G. (1967). Experimental analysis of cerebral dominance in man. In F. L. Darley (Ed.), Brain mechanisms underlying speech and language (pp. 167–184). New York: Grune & Stratton. Sackeim, H., Greenberg, M. S., Weiman, A. L., Gur, R. C., Hungerbuhler, J. P., & Geshwind, N. (1982). Hemispheric asymmetry in the expression of positive and negative emotions: Neurologic evidence. Archives of General Neurology, 39, 210–218.
524
FOGEL AND HARRIS
Schiff, B. B., Esses, V. M., & Lamon, M. (1992). Unilateral facial contractions produce mood effects on social cognitive judgements. Cognition and Emotion, 6, 357–368. Schiff, B. B., Guirguis, M., Kenwood, C., & Herman, C. P. (1998). Asymmetrical hemispheric activation and behavioral persistence: Effects of unilateral muscle contractions. Neuropsychology, 12, 526– 532. Schiff, B. B., & Lamon, M. (1989). Inducing emotion by unilateral contraction of facial muscles: A new look at hemispheric specialization and the experience of emotion, Neuropsychologia, 27, 923– 935. Schiff, B. B., & Lamon, M. (1993). Unilateral contraction of facial muscles do effect emotions: A ‘‘failed replication’s’’ failure to perform a replication. Cortex, 29, 549–551. Schiff, B. B., & Lamon, M. (1994). Inducing emotion by unilateral contraction of hand muscles. Cortex, 30, 247–254. Schiff, B. B., & Truchon, C. (1993). Effects of unilateral contraction of hand muscles on perceiver biases in the perception of chimeric and neutral faces. Neuropsychologia, 31, 1351–1365. Silberman, E. K., & Weingartner, H. (1986). Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5, 322–353. Smith, B. D., Kline, R., & Meyers, M. (1990). The differential hemispheric processing of emotion: A comparative analysis in strongly-lateralized sinistrals and dextrals. International Journal of Neuroscience, 50, 59–71. Van Whitlock, R., Lubin, B., & Noble, E. (1995). Factor analysis of the State-Trait Depression Adjective Check Lists. Journal of Clinical Psychology, 51, 614–625. Westerman, R., Spies, K., Stahl, G., & Hesses, F. W. (1996). Relative effectiveness and validity of mood induction procedures: A meta-analysis. European Journal of Social Psychology, 26, 557–580. Williams, C. W., Lees-Haley, P. R., & Price, J. R. (1998). Self-attention and reported symptoms: Implications for forensic assessment. Professional Psychology: Research and Practice, 29, 125–129. Wissing, M. P., & Wessels, S. (1992, July). Unilateral Lower Facial Contractions and Emotional Experience: An Affirmative Study. Paper presented at the 25th International Congress of Psychology, Brussels, Belgium. Wittling, W., & Roschmann, R. (1993). Emotion-related hemisphere asymmetry: Subjective emotional responses to laterally presented films. Cortex, 29, 431–448.
Do Unilateral Right and Left Face Contractions Induce Positive and Negative Emotions? A Further Test of Schiff and Lamon’s (1989) Hypothesis Travis G. Fogel School of Medicine, University of California, Los Angeles
and Lauren Julius Harris Michigan State University Published online November 16, 2001
Schiff and Lamon (1989) proposed that unilateral face contractions induce positive or negative changes in emotion depending on the side of contraction; support for this proposal, however, has been mixed. In a new test, 40 right-handed and 38 left-handed men performed four alternating face contractions (LRLR or RLRL) and, after each one, completed a different version of the Depression Adjective Checklist (Lubin, 1994). A repeated-measures ANCOVA failed to reveal any significant effect of side of face contraction or handedness on direction of emotion change. Instead, regardless of side of contraction, the subjects’ negative emotional state increased significantly across the four contractions with the degree of change being significantly related to the subjects’ reported level of difficulty in holding the contraction irrespective of whether the more difficult side was the left or the right. 2001 Elsevier Science Key Words: laterality; face contraction; emotion; valence hypothesis; handedness.
The so-called ‘‘valence hypothesis’’ for cerebral organization of emotion posits that the left and right hemispheres are specialized for the experience of positive and negative emotions, respectively, where positive emotions include cheer, elation, and confidence and negative emotions include sadness, grouchiness, and distress (Silberman & Weingartner, 1986). Support for the hypothesis has been mixed. Evidence for it has come from research on clinical and normal populations, including studies of emotional displays in persons with unilateral cerebral lesions (Sackeim et al., 1982) and in persons with epilepsy who undergo the Intracarotid Amobarbital Procedure (Ross & Rosadini, 1967) and studies of asymmetries in cortical activity in persons induced into emotional states (Davidson, Schwartz, Saron, Bennet, & Goldman, 1979) and in persons with clinical depression (Henriques & Davidson, 1991). Evidence against the hypothesis has come from research on similar clinical and normal Some of the data in this report were presented at the poster session of the 9th annual meeting of TENNET, Montreal, Canada (June, 1998). Address correspondence and reprint requests to Lauren Julius Harris, Department of Psychology, Michigan State University, Psychology Research Building, East Lansing, MI 48824. Fax: (517) 3531652. E-mail: [email protected]. 513 0278-2626/01 $35.00 2001 Elsevier Science All rights reserved.
514
FOGEL AND HARRIS
populations, including studies finding that, irrespective of valence, emotional disturbances are more common following right- than left-hemisphere injury (Lishman, 1968), that emotional changes in persons with temporal lobe epilepsy are more common in those with right- than with left-sided foci (Bear & Fedio, 1977), and that emotional responses in normal persons are stronger to happy and sad films alike when presented to the right than to the left hemisphere (Wittling & Roschmann, 1993). Over the past decade Schiff and Lamon and their colleagues have reported further support for the valence hypothesis with a new method—unilateral contractions of the lower muscles of the face. With college students as subjects and using a variety of dependent measures—response to an open-ended instruction to attend to and report on their emotional experiences (Schiff & Lamon, 1989), responses to TAT cards (Schiff & Lamon, 1989), and response to instructions to describe different ethnic groups (Schiff, Esses, & Lamon, 1992)—left-side contractions were found to produce more negative changes, right-side contractions more positive changes in emotional state.1 For left-side contractions, the effects in one experiment were dramatic, at one point producing weeping in 3 of 12 subjects (Experiment 1 in Schiff & Lamon, 1989). The same general lateralized effects also were found for men and women alike. Finally, the effects are not restricted to face contractions: The same effects have been reported for unilateral contractions of the muscles of the hand, as indexed by responses to TAT cards (Schiff & Lamon, 1994), judgments of the emotional valence of chimeric faces (Schiff & Truchon, 1993), and persistence in trying to solve unsolvable problems (Schiff, Guirguis, Kenwood, & Herman, 1998). Schiff and Lamon (1993) cite their ability to produce the valence effect under a number of different conditions as a sign of the method’s being ‘‘quite robust’’ (p. 551). To explain the effects of the contraction method, Schiff and Lamon (1989) propose a two-step mechanism: first, inasmuch as the muscles of the lower two-thirds of the face as well as the muscles of the hand are innervated predominantly by the contralateral hemisphere, unilateral contraction of these muscles is assumed to predominantly activate sensory and/or motor areas in the contralateral hemisphere; second, on the assumption that neural activation spreads to nearby cortical and limbic regions, including regions that mediate emotional states, there is arousal of the emotional state—positive or negative—primarily associated (according to the valence hypothesis) with that hemisphere. If the contraction method works as Schiff and Lamon (1989) suppose, it would provide an important new way to test the valence hypothesis in clinical as well as nonclinical populations. The main reason is that it would allow for the selective (or predominant) activation of each hemisphere while avoiding, according to Schiff and Lamon, the intervening cognitions and demand characteristics associated with more conventional emotion-induction methods, such as the use of narratives, self-statements, films, or music (for reviews, see Gerrards-Hesse, Spies, & Hess, 1994; Martin, 1990; Westermann, Spies, Stahl, & Hesse, 1996). Other than the studies by Schiff and Lamon and their colleagues, however, the method has found mixed support in the two tests that we know to have been performed in other laboratories, by Kop, Merckelbach, and Muris (1991), and by Wissing and Wessels (1992). Kop et al. (1991) failed to replicate the effect altogether and, instead, found only 1 In describing their results, Schiff and Lamon (1989) use the terms ‘‘emotional state’’ and ‘‘mood’’ interchangeably. Other researchers, however, use them differently. For example, according to Ekman (1994) and Davidson (1994), emotions are brief ‘‘phasic perturbations,’’ have a specific focus, and serve to modulate or bias action, whereas moods are longer lasting, have a more generalized focus, and serve to bias cognition. By this usage, the face-contraction method would seem to be better described as a method of emotion-induction than as a method of mood induction. In the current article, we shall use the term ‘‘emotional state’’ to avoid any misinterpretation.
FACE CONTRACTIONS AND EMOTION
515
an interaction between side of face contraction and contraction sequence such that, irrespective of side of contraction, contractions performed later in the sequence produced more negative reactions than those performed earlier in the sequence. This led Kop et al. (1991) to conclude that the operative factor was fatigue—that subjects grew more fatigued as they proceeded through the contraction sequence and that this is what was reflected in their increasingly negative reaction over this period. At the end of their experiment, Kop et al. (1991) asked their subjects which of the contractions, the left- or the right-sided, were the more difficult to maintain. The results showed that, although the emotional changes did not vary with side of contraction, they did vary according to the side that the subjects said was more difficult to maintain, with more negative reactions following contraction of the more difficult side. For some subjects, the more difficult side was the right, and for a nearly equal number of others, it was the left. In a commentary, Schiff and Lamon (1993) pointed to two features of Kop et al.’s (1991) procedure that could have interfered with their subjects’ awareness of changes in their emotional state as well as with their ability to report on these changes. The first was in the contraction sequence. Whereas Schiff and Lamon (1989) used straight alternation (LRLR or RLRL), Kop et al. used a massed-trial procedure (three sameside contractions before alternation, LLLRRR or RRRLLL). Schiff and Lamon (1993) suggested that straight alternation, with subjects reporting after each contraction, better allows subjects to compare differences between sides, thereby enhancing the saliency of their emotional experiences and facilitating their awareness of them (see also Schiff et al., 1998). They based this supposition on data (Schiff, Esses, & Lamon, 1992) indicating that straight alternation produced more frequent and reliable changes in emotional states than did massed trials. The second feature was the dependent measure. Kop et al. (1991) had their subjects do two things: evaluate the favorableness of a human cartoon face after each one of the total of six contractions and also report on their own emotional state after the third contraction of each set of the three consecutive left- or right-side contractions. Schiff and Lamon (1993) speculated that the subjects’ self-reports of emotional states following the three consecutive contractions may have been affected by the prior evaluations of the cartoon drawings made after each contraction, that is, that the subjects’ emotional state may have been influenced by their cartoon evaluations as well as by their face contractions. In their reply, Kop et al. (1993) pointed to what they regarded as shortcomings in Schiff and Lamon’s (1989) own experimental procedure and therefore concluded that, in light of their own evidence on difficulty of contraction, ‘‘it remains to be seen whether unilateral contraction effects reported by Schiff and Lamon need a neuropsychological explanation’’ (p. 554). If Schiff and Lamon’s (1993) criticisms are reasonable, they are, in any case, vitiated by the study by Wissing and Wessels (1992). The reason is that when Wissing and Wessels used Kop et al.’s (1991) massed-trial procedure, they found the valence effect only when they had their subjects, after each face contraction, point to the one face on a card displaying photographs of 10 faces whose emotional expression most clearly matched their own emotional state during the contraction (5 faces showed positive expressions and 5 showed negative expressions), and even under this condition, the valence effect was shown only by men, not women. When, however, Wissing and Wessels had their subjects make open-ended reports of their emotional state after each contraction similar to the kind of reports relied on by Schiff and Lamon (1989), no valence effect was found. Instead, for both sexes, negative reports predominated, irrespective of side of contraction, just as Kop et al. (1991) had found. Unlike Kop et al. (1991), however, Wissing and Wessels did not ask their subjects to report on
516
FOGEL AND HARRIS
the difficulty of contraction, which means that they could not assess its relation to their subjects’ emotional states. Furthermore, even though they collected self-reports of emotional state after each contraction, their analyses included only the sum total of reports after left- and right-side contractions, which means that they could not assess possible effects of order of contraction or of fatigue on emotional state. Finally, unlike Schiff and Lamon (1989), Wissing and Wessels failed to include any precontraction measure of emotional state, which means that they could not take into account the possible relation between initial emotional state and subsequent changes in that state. Our goal in the current study was to further examine Schiff and Lamon’s (1989) hypothesis using the same face-contraction sequence as they used as well as the same method of producing the contraction. In this way, we hoped to avoid the difficulties in interpretation that faced Kop et al. (1991) in their failed replication. The only difference was in the dependent measures. In place of the TAT and the open-ended report of emotional state used by Schiff and Lamon (1989), we measured self-report of emotional state after each contraction on a standardized adjective check list with several parallel forms. This allowed us to quantify the degree of change in emotional state across contractions. Like Schiff and Lamon (1989), we also administered the check list prior to the first contraction in order to control statistically for initial emotional state. Finally, for 62 of the 78 subjects, we included a difficulty-of-contraction measure so that we could assess any possible relation between emotional state changes and the relative difficulty of holding each side of the face in the contracted position.2 Given that Schiff and Lamon (1989) found the effect in both sexes, whereas Wissing and Wessels (1992) found it only in men, we confined our study to men to maximize the likelihood of finding an effect. Finally, in all of the studies by Schiff and colleagues, as well as in the studies by Kop et al. (1991) and Wissing and Wessels (1992), only right-handers were tested. We expanded our sample to include lefthanders. We did this for two reasons. First, because left-handers are reported to differ from right-handers on select psychological tasks and to be more common in certain clinical and other special populations (e.g., Harburg, Roeper, Ozgoren, & Feldstein, 1981; Hicks & Pelligrini, 1978; see review in Harris, 1992), we were curious to see whether left- and right-handers also would differ in overall frequency and intensity of negative and positive emotions after face contraction. Prior studies of handedness and the experience of emotion are of uncertain guidance here, with left-handers sometimes showing asymmetries similar in size and direction to those shown by righthanders (e.g., Robinson, Lipsey, Bolla-Wilson, et al., 1985), other times smaller but in the same direction (e.g., Smith, Kline, & Meyers, 1990), and still other times in the reverse direction (e.g., McFarland & Kennison, 1989). The face-contraction method, and its claimed ability to bypass intervening cognitions common to conventional induction methods, thus may prove useful for comparing the neuropsychological organization of emotion in left- and right-handers. Second, left-handers and righthanders reportedly differ in the side of the face they find more ‘‘convenient’’ to move when asked to perform facial exercises, including lateral movements of the angle of the mouth, winking, platysma contraction, raising and everting the upper lip with dilation of the nostril, and vertical wrinkling of the forehead, with right-side movements more ‘‘convenient’’ for right-handers and left-side movements more ‘‘conve2
Although we already knew of Kop et al.’s (1993) finding, this question had not been part of our original design. We added it to the protocol only after several subjects among the first 16 tested reported spontaneously that one side of the face was harder to hold in the contracted position than the other side. Only then did we realize the potential importance of Kop et al.’s finding.
FACE CONTRACTIONS AND EMOTION
517
nient’’ for left-handers (Chaurasia & Goswami, 1975). Assuming that the authors’ term ‘‘convenient’’ refers to level of difficulty, the results suggests the possibility of a relation between handedness, side of greater difficulty in performing the face contraction, and the direction and degree of change in emotional state. In sum, if Schiff and Lamon’s (1989) face-contraction method works as they suppose, and if the valence hypothesis is correct, then negative emotional state should increase following left-side contractions and should decrease following right-side contractions. The outcome in left-handers is harder to predict for reasons noted above. At the least, any emotional state changes in left-handers might be expected to be smaller or more variable than those in right-handers. METHOD
Subjects The subjects were 78 undergraduate college men (49 right-handed and 38 left-handed, mean age ⫽ 20.1 years). All were volunteers from introductory psychology courses who participated for course credit, and all were tested following protocols approved by the Michigan State University Committee on Research Involving Human Subjects. On a medical screening questionnaire, none of the subjects reported current or past brain damage, paralysis, injury, muscle weakness, clinical depression, or any other conditions that could be possible sources of confounding. Subjects were randomly assigned to either the LRLR or RLRL contraction-order condition with the constraint that each condition included an equal number of right- and left-handers. Handedness was assessed on an eight-item modified version of the Edinburgh Handedness Inventory (Oldfield, 1979).
Face Contraction Schiff and Lamon’s (1989) instructions for producing the unilateral face contractions were followed as closely as possible. The experimenter (T.G.F.), facing the subject, began by explaining how the subject was to perform the facial manipulation. The experimenter said, ‘‘I want you to pull back and raise the [left/right] side of your mouth as much as you can, just like this.’’ The instruction named the left side for subjects in the LRLR condition and the right side in the RLRL condition, and, for each condition, the experimenter demonstrated by making the movement himself. The experimenter then said, ‘‘Now you try it.’’ After the subject successfully made the required movement, the experimenter said, ‘‘That’s fine. When the experiment starts, I want you to hold it in that position for forty-five seconds until I say relax.’’ The subject also was told to breathe normally during the contraction, to maintain eye contact with the experimenter, and to pay close attention to his emotions, to ‘‘how you are feeling,’’ rather than to his thoughts or facial sensory experiences. The intention behind this last instruction was to minimize the subject’s focus on peripheral/physical sensations during the contraction, such as the difficulty of holding the position, which, as already noted, Kop et al. (1991) found could affect emotional state. If necessary, further instructions were given until both the subject and experimenter agreed that the subject understood how to perform the contraction. Further instructions were needed for seven subjects, all of whom showed too small a contraction on their first attempt. All succeeded on a second attempt. In each contraction-order condition, LRLR or RLRL, subjects completed a series of four contractions, each lasting 45 s, with the side of contraction alternating each time. After each contraction, subjects were instructed to relax and to complete a different version of a short check list designed to measure their emotional state.
Test Materials Depression Adjective Check List (DACL). Because we wanted to assess changes in emotional states after each contraction, the instrument we chose was one that could be administered quickly and repeatedly, the Depression Adjective Check List, or DACL (Lubin, 1981, 1994). The DACL is a multipleitem paper-and-pencil check list designed to measure transient emotional states. It has well-established norms and high test–retest reliability in college students (Lubin, Van Whitlock, Swearngin, & Seever, 1993), can be administered quickly (1–2 min), and has several parallel forms designed for use in research, in particular for research using repeated measures. It also has been frequently used to measure changes in emotional state, and its sensitivity to such changes is well documented (e.g., Lubin, Swearngin, &
518
FOGEL AND HARRIS
Seaton, 1992; Lubin & Van Whitlock, 1993; Lubin, Van Whitlock, Swearngin, & Seever, 1993; Lubin, Van Whitlock, McCollum, et al., 1994). The different parallel forms are A, B, C, and D, each with 22 negative adjectives and 10 positive adjectives, and Form G, with 22 negative adjectives and 12 positive adjectives. The different forms are highly intercorrelated (.85–.92; Lubin, 1994), and a factor analysis reveals two factors: depressive affect and positive affect (Van Whitlock, Lubin, & Noble, 1995). The manual provides conversion tables and scoring forms for each test form for both T scores and percentile scores for state-negative moods, state-positive moods, and state mood total. The state mood total is calculated as the sum of positive adjectives endorsed (i.e., state-negative mood) and the number of positive adjectives not endorsed (i.e., 10 minus the state-positive mood for DACL A, B, C, and D, and 12 minus the state-positive mood for DACL-G) or State-Total ⫽ 10 ⫺ State Positive ⫹ State Negative). For purposes of this study, only the state mood total T scores were used in any statistical analyses using the DACL. Difficulty-of-contraction question. To measure self-reported difficulty of holding each side of the face in the contracted position, subjects were asked, at the end of the experiment, which contraction— left or right—was more difficult to hold and to record their answer on a 9-point scale, ranging from 1 (Left Side More Difficult) to 9 (Right Side More Difficult), with 5 (Same Difficulty) as a midpoint.
Procedure Subjects were tested individually in a small, quiet room with only the experimenter present. Subjects first provided written consent and completed the handedness measure and the first of the five different forms of the DACL. After becoming familiar with the procedure for performing the contraction, subjects completed the series of four contractions (45 s each). After each one, they completed another of the remaining forms of the DACL. At the end of the experiment, they were asked the difficulty-of-contraction question.
Design A 2 ⫻ 2 ⫻ 4 mixed design was used, with handedness (left or right) and contraction-order condition (LRLR or RLRL) as between-subjects variables and with sequence position (first, second, third, or fourth contraction) as the within-subjects variable. With this design, the test of the valence hypothesis comes not from comparison of the contraction-order conditions but from the assessment of the interaction between contraction-order condition and sequence position.
RESULTS
Side of Contraction DACL T scores were first calculated using the conversion tables for the DACL state mood total (Lubin, 1994). The results are summarized in Table 1 and show the mean DACL T scores after left and right contractions for each handedness group in each contraction condition. A 2 ⫻ 2 ⫻ 4 repeated-measures analysis of covariance (ANCOVA) was performed on the DACL T scores, with emotional state prior to first contraction as a covariate. The results failed to show a significant main effect for contraction-order condition, F(1, 73) ⫽ 1.05, p ⫽ .31, or for the interaction of contraction order by sequence position, F(3, 219) ⫽ 2.43, p ⫽ .07, indicating that side of contraction and DACL scores were unrelated. With one exception, all other main effects and interactions were also nonsignificant [handedness, F(1, 73) ⫽ 2.80, p ⫽ .10; handedness ⫻ sequence position, F(3, 219) ⬍ 1; handedness ⫻ side of contraction ⫻ sequence position, F(3, 219) ⫽ 2.29, p ⫽ .08]. The exception was for position of the contraction in the sequence, F(3, 219) ⫽ 8.52, p ⬍ .001. The results showed that DACL scores increased significantly across the sequence of four contractions, indicating that the subjects’ emotional state grew worse, or more negative, over this period.
519
FACE CONTRACTIONS AND EMOTION
TABLE 1 Effects of Handedness, Contraction Condition, Sequence Position on Mean DACL T Scores Sequence Contraction order
Precontraction DACL-A
1 DACL-B
2 DACL-C
3 DACL-D
4 DACL-G
RLRL Total Group (n ⫽ 38) Right-Handers (n ⫽ 19) Left-Handers (n ⫽ 19)
46.1 (22.0) 45.6 (23.7) 46.5 (19.0)
R 53.4 (22.1) 55.0 (23.5) 51.9 (21.1)
L 55.0 (20.8) 64.3 (17.0) 45.6 (20.5)
R 62.6 (20.0) 66.9 (20.3) 58.2 (19.1)
L 68.0 (20.0) 71.2 (22.8) 64.7 (16.7)
LRLR Total Group (n ⫽ 40) Right-Handers (n ⫽ 21) Left-Handers (n ⫽ 19)
39.2 (20.6) 39.8 (22.2) 38.5 (19.3)
L 52.0 (24.1) 54.1 (27.5) 49.6 (20.2)
R 63.8 (21.6) 62.2 (24.7) 65.5 (18.3)
L 60.2 (22.7) 61.7 (24.5) 58.4 (21.0)
R 65.0 (22.5) 67.1 (22.2) 62.7 (23.2)
Note. Standard deviations are in parentheses.
Difficulty-of-Contraction Effects To determine whether subjects’ self-reported difficulty in performing the left- and right-side contractions was related to their changes in emotional state (DACL scores), subjects were grouped into left- or right-face groups based on their response to the 9-point scale question. As noted above, only 62 of the 78 subjects made this selfrating, and of this number, 26 (41.9%) indicated that left-side contractions were more difficult, 31 (50%) indicated that right-side contractions were more difficult, χ 2(1, N ⫽ 57) ⫽ p ⫽ .439, and 5 (8.1%) indicated that both were equally difficult. Of the 26 subjects for whom left-side contractions were more difficult, 17 (65.3%) came from the RLRL group; in contrast, of the 31 subjects for whom right-side contractions were more difficult, 21 (67.7%) came from the LRLR group, χ 2 (1, N ⫽ 57) ⫽ p ⬍ .05. Thus, order of sequence and face-contraction difficulty were related, with the subjects in the RLRL condition more likely to judge the left contractions as more difficult, and the subjects in the LRLR condition more likely to judge the right contractions as more difficult. Contrary to prior evidence (Chaurasia & Goswami, 1975), handedness proved to be unrelated to side of greater difficulty, χ 2 (1, N ⫽ 57) ⫽ p ⫽ .57. To test the relation between difficulty of contraction and emotional state in the two handedness groups, a 2 (left vs right more difficult) ⫻ 2 (side of contraction) ⫻ 2 (left- or right-handed) ANOVA was performed on the DACL T scores. The analysis failed to show significant main effects for difficulty of contraction, F(1, 53) ⬍ 1, side, F(1, 53) ⬍ 1, or handedness F(1, 53) ⫽ 2.23, p ⫽ .14. All interactions were nonsignificant except for the one between difficulty of contraction and side of contraction, F(1, 53) ⫽ 9.11, p ⬍. 01. That is, subjects who reported that left contractions were more difficult also reported experiencing more negative emotional states (higher DACL scores) after left than after right contractions. Likewise, subjects who reported that right contractions were more difficult reported experiencing more negative emotional states after right than after left contractions (see Table 2).
520
FOGEL AND HARRIS
TABLE 2 Reported Contraction Difficulty and Side of Contraction on DACL T Scores Side of contraction Contraction difficulty
Left
Right
Left Side More Difficult (n ⫽ 26) Right Side More Difficult (n ⫽ 31)
130.2 (45.7) 108.2 (41.0)
115.7 (42.0) 119.7 (41.1)
Note. DACL T scores for side of contraction reflect the sum of the two left-sided contractions and the sum of the two rightsided contractions.
DISCUSSION
Despite our close adherence to Schiff and Lamon’s (1989) procedure for producing the face contractions, we found no evidence that, in normal persons, positive and negative emotional changes are related to side of contraction, and thus we found no support for the valence hypothesis using this method. The results instead showed a significant increase in negative emotional state over time, regardless of side of contraction, and a significant relation between the reported difficulty in holding the contraction and the degree of negative emotional state. With respect to the valence hypothesis, we can think of at least four possible reasons for our null results. First, Schiff and Lamon (1989) reported that in one of their studies, changes in emotional states did not appear until the third and fourth contractions. Our null effects, therefore, may have resulted from our having used DACL scores from all four contractions in our analyses. To check this possibility, we reexamined the data using only the last two contractions in the RLRL condition and the last two in the LRLR condition. The results were unchanged. That is, all main effects and interactions were nonsignificant except for position of contraction in the sequence. In other words, the new analysis showed that emotional state was more negative after the last, or fourth contraction, whether L or R, than after the third contraction. The second possibility is that the DACL, despite its wide and successful use as a measure of changes in emotional state, is insufficiently sensitive to the emotional changes induced by unilateral face contraction. But this seems unlikely, given that the DACL did disclose the overall change in our subjects’ emotional states from precontraction to the fourth contraction, with the average change exceeding 1 standard deviation (see Table 1). It therefore seems highly likely that it would have been sensitive as well to the weeping that, as noted above, Schiff and Lamon (1989) observed in one of their first experiments, although none of our 78 subjects showed any such reaction. That the DACL was sufficiently sensitive also is indicated by the demonstrated relation between our subjects’ DACL scores and their self-reported difficulty of holding the contraction. The third possibility is that our having included all DACL scores in the analyses washed out any effect that existed in the first place. In Schiff and Lamon’s (1989) second experiment, which measured self-report after each face contraction, only 22 of 30 subjects produced any ‘‘classifiable’’ responses at all (i.e., reports of negative, positive, or neutral emotional state), and of the total of 120 responses made by these 22 subjects, only 56 responses (46.7%) could be classified as having followed left
FACE CONTRACTIONS AND EMOTION
521
or right contractions. The other responses could not be classified. If, as these figures suggest, emotional states are reported relatively infrequently, occurring less than half the time, it raises the possibility that even though our dependent measure yielded quantitative scores, our use of all reports of emotional state from all contractions on all subjects somehow obfuscated any changes like those found by Schiff and Lamon (1989). Wissing and Wessels (1992), however, used all responses in their analyses, and theirs, as noted above, was the only successful, or rather partially successful, replication to date other than those by Schiff, Lamon, and colleagues themselves. Nevertheless, to check this possibility, we reexamined our data for only those subjects reporting changes in emotional states that were significantly different from their precontraction levels. We defined such individuals by two separate methods and performed two separate statistical analyses for each method—an ANCOVA using all four contractions in the sequence and an ANCOVA using only the last two contractions. For the first method, we selected subjects who showed at least a 1 standard deviation change in DACL scores from precontraction to the fourth and final contraction in the sequence, where the standard deviation was determined using the total sample standard deviation of precontraction scores. By this method, 39 (50%) subjects met criterion, similar to the percentage of ‘‘classifiable responses’’ reported by Schiff and Lamon (1989). Reexamination of the data using this method, however, did not change the results: for four contractions, F(3, 120) ⫽ 1.38, p ⫽ .251; for the last two contractions, F(3, 40) ⬍ 1. For the second method, we selected the top 25% of subjects who produced the largest changes in emotional state from precontraction to fourth contraction. Again, the results were unchanged: for four contractions, F(3, 54) ⫽ 1.30, p ⫽ .284; for the last two contractions, F(1, 17) ⬍ 1. Regardless, then, of the method of analysis or subject selection, the results remained unchanged. The fourth possibility is that the difficulty of holding the contraction had a more salient effect on emotional state than did any changes associated with side of contraction per the valence hypothesis. Like Kop et al. (1991), we found an association between negative emotional state and the reported difficulty of holding the contraction, and, also like Kop et al., we found that approximately the same number of subjects rated the left-side contractions as more difficult as rated the right-side contractions as more difficult. These results, along with our finding that subjects’ negative emotional state increased across the sequence of contractions, suggest that the DACL scores reflect the fatigue of holding the contraction. They, therefore, also suggest that our subjects’ emotional states were linked to their physical sensations even though we instructed them to focus on their emotions. In this connection, it is noteworthy that Schiff and Lamon (1989) reported that their subjects’ ‘‘unclassifiable’’ responses included reports of facial sensory experiences. If, therefore, the valence hypothesis is correct and if the face-contraction method is a valid way to induce emotional states, it suggests that any cerebrally mediated differences in emotional state induced by face contraction may have been overpowered by attention to the physical difficulty of the contraction. This possibility is supported by a recent study by Williams, Lees-Haley, and Price (1998). In an ‘‘undivided self-attention’’ condition, one group of normal adults was instructed to attend to their thoughts, feelings, and sensations and to report any physical symptoms and emotional symptoms related to anxiety and depression on a measure of physical complaints and disposition to report symptoms (Pennepacker Inventory of Limbid Languidness; Pennepacker, 1982) and on a measure of mood, or affective states (Profile of Mood States; McNain, Lorr, & Droppleman, 1981). In a ‘‘self-distraction’’ condition, another group was asked to keep a mental tally of the number of items in the inventory related to physical versus emotional symptoms. The result was that physical symptoms and reports of anxiety and depression were greater after self-attention instructions than after self-
522
FOGEL AND HARRIS
distraction instructions. If we were to liken our subjects to Williams et al.’s selfattention group, it would suggest that our subjects’ increases in negative emotional states across contractions may have been due, in large measure, to self-attention to internal states. Preliminary support for this suggestion comes from a recent study conducted in our laboratory in which one group of normal adults (face group) performed four unilateral face contractions and another group (face-hand group) performed four unilateral face contractions while simultaneously making contractions of the hand on the same side. On the DACL, administered following the fourth contraction, the face group reported increases in negative emotional states regardless of side of contraction, just as we found in the current study, whereas the face-hand group showed no significant changes in emotional state. This suggests that in the face-hand group, the hand contraction may have diminished the subjects’ attention to the sensation of the face contraction, similar to the distraction condition in the Williams et al. (1998) study.
SUMMARY
Although all of these possibilities deserve consideration, our null results, in the end, provide no support for Schiff and Lamon’s (1989) conclusions pertaining to the effects of the face-contraction method. It is difficult to say what this means in terms of the valence hypothesis for the experience of emotion. For instance, the absence of differences between contraction side and emotional state may cast doubt on the valence hypothesis for the experience of emotion, or it may simply mean that we failed to find any difference for one or more of the reasons discussed above. Likewise, our null results for handedness could mean that the neuropsychological organization for the experience of emotion is the same in right- and left-handers, consistent with certain other studies, or that differences do not appear for some of the same reasons already discussed. In summary, our results, like those of Kop et al. (1991), question the proposition that left- and right-side face (or hand) contractions produce different changes in emotional state. Schiff and Lamon (1993) cite their ability to produce the valence effect with different measures under different conditions as a sign of their method’s ‘‘robustness,’’ but a robust method ought to yield reproducible effects in other laboratories. To date, the face-contraction method has not met this criterion. We therefore suggest that before it can be accepted as a method for testing the valence hypothesis, it needs further study. In particular, dependent measures must be developed that are maximally sensitive to the effects of the face contractions while also controlling for the effects of the physical effort of making and holding the contractions. Until then, we concur with Kop et al.’s (1993) conclusion that ‘‘it remains to be seen whether the unilateral contraction effects reported by Schiff and Lamon need a neuropsychological interpretation’’ (p. 554). In other words, we cannot rule out the possibility that the effects represent only the action of peripheral, or muscular, cues.
REFERENCES Bear, D. M., & Fedio, P. (1977). Quantitative analysis of interictal behavior in temporal lobe epilepsy. Archives of Neurology, 34, 454–467. Borod, J. C., Caron, H. S., & Koff, E. (1987). Asymmetry of facial expression related to handedness, footedness, and eyedness: A quantitative study. Cortex, 17, 381–390.
FACE CONTRACTIONS AND EMOTION
523
Bulman-Fleming, M. B., & Bryden, M. P. (1994). Simultaneous verbal and affective laterality effects. Neuropsychologia, 32, 787–797. Chaurasia, B. D., & Goswami, H. K. (1975). Functional asymmetry in the face. Acta Anatomica, 91, 154–160. Davidson, R. J. (1994). On emotion, mood, and related affective constructions. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion: Fundamental questions (pp. 51–55). New York: Oxford Univ. Press. Davidson, R. J., Schwartz, G. E., Saron, C., Bennett, J., & Goldman, D. J. (1979). Frontal vs. parietal EEG asymmetry during positive and negative affect. Psychophysiology, 16, 202–203. [Abstract] Ekman, P. (1994). Moods, emotions, and traits. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion: Fundamental questions (pp. 56–58). New York: Oxford Univ. Press. Gerrards-Hesse, A., Spies, K., & Hesse, F. W. (1994). Experimental inductions of emotional states and their effectiveness: A review. British Journal of Psychology, 85, 55–78. Harburg, E., Roeper, P., Ozgoren, F., & Feldstein, A. M. (1981). Handedness and temperament. Perceptual and Motor Skills, 52, 283–290. Harris, L. J. (1992) Left-handedness. In I. Rapin & S. J. Segalowitz (Eds.), Handbook of neuropsychology: Child neuropsychology (Vol. 6, pp. 145–208). Amsterdam: Elsevier. Henriques, J. B., & Davidson, R. J. (1991). Left frontal hypoactivation in depression. Journal of Abnormal Psychology, 100, 535–545. Hicks, J. B., & Pelligrini, R. J. (1978). Handedness and anxiety. Cortex, 14, 119–121. Kop, W. J., Merckelbach, H., & Muris, P. (1991). Unilateral contraction of facial muscles and emotion: A failed replication. Cortex, 27, 101–104. Kop, W. J., Merckelbach, H., & Muris, P. (1993). Unilateral contraction and induction of emotion: A reply to Schiff and Lamon. Cortex, 29, 553–554. Lishman, W. A. (1968). Brain injury in relation to psychiatric disability after head injury. British Journal of Psychiatry, 114, 373–410. Lubin, B. (1981). The State Trait Depression Adjective Check Lists. San Diego, CA: Educational and Industrial Testing Services. Lubin, B. (1994). The State Trait-Depression Adjective Check Lists Manual. Odessa, FL: Psychological Assessment Resources. Lubin, B., Swearngin, S. E., & Seaton, K. (1992). Research with the Depression Adjective Check Lists, 1965–1991. Odessa, FL: Psychological Assessment Resources. Lubin, B., & Van Whitlock, R. (1993). Diagnostic efficiency of the Depression Adjective Check Lists. Journal of Clinical Psychology, 49, 695–701. Lubin, Van Whitlock, R., McCollum, K. L., Thummel, H., Denman, N., & Powers, M. (1994). Measuring the short-term mood of adolescents: Reliability and validity of the state form of the Depression Adjective Check Lists. Adolescence, 29, 591–604. Lubin, B., Van Whitlock, R., Swearngin, S. E., & Seever, M. (1993). Self-assessment of state and trait depressive affect by college students: Reliability and validity of an adjective check list. Journal of College Students Development, 34, 249–255. Martin, M. (1990). On the induction of mood. Clinical Psychology Review, 10, 669–697. McFarland, R. A., & Kennison, R. (1989). Handedness affects emotions valence asymmetry. Perceptual and Motor Skills, 68, 435–441. McNair, D. M., Lorr, M., & Droppleman, L. F. (1981). Profile of Mood States Manual. San Diego, CA: Educational and Industrial Testing Service. Oldfield, R. C. (1979). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97–113. Pennepacker, J. W. (1982). The psychology of physical symptoms. New York: Springer-Verlag. Robinson, R. G., Lipsey, J. R., Bolla-Wilson, K., Bolduc, P. L., Pearlson, G. D., Rao, K., & Price, T. R. (1985). Mood disorders in left-handed stroke patients. American Journal of Psychiatry, 142, 1424–1429. Ross, G. F., & Rosadini, G. (1967). Experimental analysis of cerebral dominance in man. In F. L. Darley (Ed.), Brain mechanisms underlying speech and language (pp. 167–184). New York: Grune & Stratton. Sackeim, H., Greenberg, M. S., Weiman, A. L., Gur, R. C., Hungerbuhler, J. P., & Geshwind, N. (1982). Hemispheric asymmetry in the expression of positive and negative emotions: Neurologic evidence. Archives of General Neurology, 39, 210–218.
524
FOGEL AND HARRIS
Schiff, B. B., Esses, V. M., & Lamon, M. (1992). Unilateral facial contractions produce mood effects on social cognitive judgements. Cognition and Emotion, 6, 357–368. Schiff, B. B., Guirguis, M., Kenwood, C., & Herman, C. P. (1998). Asymmetrical hemispheric activation and behavioral persistence: Effects of unilateral muscle contractions. Neuropsychology, 12, 526– 532. Schiff, B. B., & Lamon, M. (1989). Inducing emotion by unilateral contraction of facial muscles: A new look at hemispheric specialization and the experience of emotion, Neuropsychologia, 27, 923– 935. Schiff, B. B., & Lamon, M. (1993). Unilateral contraction of facial muscles do effect emotions: A ‘‘failed replication’s’’ failure to perform a replication. Cortex, 29, 549–551. Schiff, B. B., & Lamon, M. (1994). Inducing emotion by unilateral contraction of hand muscles. Cortex, 30, 247–254. Schiff, B. B., & Truchon, C. (1993). Effects of unilateral contraction of hand muscles on perceiver biases in the perception of chimeric and neutral faces. Neuropsychologia, 31, 1351–1365. Silberman, E. K., & Weingartner, H. (1986). Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5, 322–353. Smith, B. D., Kline, R., & Meyers, M. (1990). The differential hemispheric processing of emotion: A comparative analysis in strongly-lateralized sinistrals and dextrals. International Journal of Neuroscience, 50, 59–71. Van Whitlock, R., Lubin, B., & Noble, E. (1995). Factor analysis of the State-Trait Depression Adjective Check Lists. Journal of Clinical Psychology, 51, 614–625. Westerman, R., Spies, K., Stahl, G., & Hesses, F. W. (1996). Relative effectiveness and validity of mood induction procedures: A meta-analysis. European Journal of Social Psychology, 26, 557–580. Williams, C. W., Lees-Haley, P. R., & Price, J. R. (1998). Self-attention and reported symptoms: Implications for forensic assessment. Professional Psychology: Research and Practice, 29, 125–129. Wissing, M. P., & Wessels, S. (1992, July). Unilateral Lower Facial Contractions and Emotional Experience: An Affirmative Study. Paper presented at the 25th International Congress of Psychology, Brussels, Belgium. Wittling, W., & Roschmann, R. (1993). Emotion-related hemisphere asymmetry: Subjective emotional responses to laterally presented films. Cortex, 29, 431–448.