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Unilateral Contraction and Induction of Emotion: A Reply to Schiff and Lamon
CONTROVERSIES UNILATERAL CONTRACTION AND INDUCTION OF EMOTION: A REPLY TO SCHIFF AND LAMON Willem Johan Kopt, Harald Merckelbach2 and Peter Muris3 (!Department of Medical Psychology and 2Department of Mental Health Sciences, University of Limburg, and 3Department of Clinical Psychology, University of Amsterdam, The Netherlands)
Schiff and Lamon (1989) carried out three studies in which they found that contraction of left facial muscles (i.e., the left corner of the mouth) elicits a dysphoric mood, whereas contraction of the right facial muscles (i.e., the right corner of the mouth) induces a positive mood. Assuming that unilateral facial muscle contraction activates the contralateral hemisphere, their findings are in accordance with neuropsychological theories that attribute a positive emotional tone to the left hemisphere and a negative tone to the right hemisphere (e.g., see review by Silberman and Weingartner, 1986). However, the results presented by Schiff and Lamon are based on an experimental procedure that is far from perfect. To begin with, the experimenters in the Schiff and Lamon studies were all familiar with the expected outcome. Furthermore, mood effects were inferred from verbalizations of subjects who performed unilateral contractions. Then, these verbalizations were evaluated by judges with criteria that were not specified. Thus, conclusions about the mood effects of unilateral contractions were, at best, based on inferential measures rather than direct observations. Using a procedure that avoided these methodological shortcomings, we recently made an attempt to validate the mood effects of unilateral contractions (Kop, Merckelbach and Muris, 1991). The results were disappointing: no evidence was found to suggest that negative mood effects and positive mood effects occur as a result of left and right muscle contraction, respectively. In their present commentary, Schiff and Lamon (this issue) cast doubts on the significance of this failure to replicate their findings. Their main argument is that our study did not follow the experimental setup employed by Schiff and Lamon (1989) and therefore did not provide a pure replication. In a strict sense, this is true of course. But, as stated before, their experimental procedure was far from perfect and, therefore, imitating such a procedure makes no sense. Apart from this fundamental issue, Schiff and Lamon raise three technical points about our study: the possible interference between stimulus material and mood, the order of unilateral contractions, and the stimulus material used. We will briefly comment on each point. As for the first point, in the Kop et al. study, subjects performed three successive left (LLL) and then three successive right (RRR) facial contractions, or vice versa. After each contraction, they were required to rate a cartoon on pleasantness. After three consecutive (LLL or RRR) contractions, mood measures were obtained. Schiff and Lamon argue that the cartoons might have interfered with the mood measures, thereby preventing an emotional effect of unilateral contraction. This, however, is very unlikely since subjects were familiar with the cartoons (subjects saw them during a pre-experimental baseline), the cartoons were emotionally neutral (see below), and they were presented in a counter-balanced fashion (which rules out any differential effect of the cartoons on mood). Note that by using the interference argument, Schiff and Lamon seem to acknowledge that the emotional effects of unilateral contraction are fragile, rather than "robust". This is remarkable because they also reported that three out of 12 subjects began to weep after left facial contraction, a finding that suggests that such manipulations have powerful Cortex, (1993) 29, 553-554
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W.J. Kop and Others
effects (Schiff and Lamon, 1989, experiment I, p. 926). The order of muscle contraction in our study was LLLRRR (or RRRLLL). Schiff and Lamon (1989) used LRLR (or RLRL) in one of their studies. We fully agree with Schiff and Lamon that "there is no a priori reason for believing that the pattern of the sequence of contractions would influence the results". But, then it is argued by Schiff and Lamon that the salience of the emotional experience is enhanced through the contrast that is brought about by alternating left-right contractions. We are not in the position to evaluate the empirical basis of this claim. For the moment, we find this argument hardly convincing. Firstly, because the contrast of left-right contraction was absent in the third experiment described by Schiff and Lamon (i.e., a between-subject design was used), and emotional effects of unilateral contraction did nevertheless emerge. Secondly, every subject in the Kop et al. study did contract both sides of the face (i.e., a within-subject design was employed) and, hence each could, in principle, have experienced the contrast between left and right contractions. The third point advanced by Schiff and Lamon concerns the stimulus material that we used for documenting the effects of unilateral contractions. In our study, subjects rated a cartoon on pleasantness in the last 5 seconds during unilateral muscle contraction. Schiff and Lamon suspect that the use of a structured cartoon rather than an ambiguous stimulus can account for our failure to validate their results: the cartoon might itself have had an emotional effect that consequently overshadowed the effects of contractions. This suggestion is refuted by the data of our experiment. Before the experiment started (i.e., during the baseline period), the pleasantness of the cartoons was rated as rather moderate (mean= 5.5) on a visual analog scale (I= "I like this picture very much"; 10 = "I don't like this picture at all"). Thus, it seems fair to conclude that the cartoons were relatively neutral. In sum, we feel that the Kop et al. (1991) study represents an adequate attempt to replicate the findings previously reported by Schiff and Lamon. Why, then, was this study unable to demonstrate emotional effects of unilateral contractions? There are two possibilities. Firstly, Schiff and Lamon argue that they ruled out a motor-effort explanation in one of their experiments, by asking subjects which unilateral contraction they experienced as more difficult to perform. However, details about this part of their study are missing (e.g. when were the subjects asked?; was there a practice effect across trials?; what was the format of the answer categories? etc.). We therefore maintain that this point needs further clarification. Secondly, it is not unreasonable to suppose that the expectations of the experimenter play a role in the emotional consequences of unilateral contraction. In the Schiff and Lamon studies, the experimenters were familiar with the hypothesis to be tested. This was not the case in our experiment. To take this argument one step further, the Schiff and Lamon studies might be a subtle version of the famous Schachter and Singer experiment (Schachter and Singer, 1962). More specifically, asking subjects to pull back and lift one corner of the mouth for about 1 minute in front of an experimenter is an embarrassing, and therefore socially arousing task. Under this condition, the experimenter could shape the hedonic tone of the arousal by providing subtle positive or negative cues. Future studies should examine the plausibility of this explanation. Meanwhile, it remains to be seen whether the unilateral contraction effects reported by Schiff and Lamon need a neuropsychological interpretation. REFERENCES
H., and MuRIS, P. Unilateral contractions of facial muscles and emotion: a failed replication. Cortex, 27: 101-104, 1991. ScHACHTER, S., and SINGER, J. Cognitive, social, and physiological determinants of emotional state. Psychological Review, 69: 379-399, 1962. ScHIFF, B.B., and LAMON, M. Inducing emotion by unilateral contraction of facial muscles. Neuropsychologia, 27: 923-935, 1989. ScHIFF, B.B., and LAMON, M. Unilateral contraction of facial muscles do effect emotions: A "failed replication's" failure to perform a replication. Cortex, 1993 (this issue). SILBERMAN, E.K., and WEINGARTNER, H. Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5: 322-353, 1986. KoP, W.J., MERCKELBACH,
W.J. Kop, Department of Medical Psychology, University of Limburg, P.O. Box 616, 6200 MD. Maastricht, the Netherlands.
Schiff and Lamon (1989) carried out three studies in which they found that contraction of left facial muscles (i.e., the left corner of the mouth) elicits a dysphoric mood, whereas contraction of the right facial muscles (i.e., the right corner of the mouth) induces a positive mood. Assuming that unilateral facial muscle contraction activates the contralateral hemisphere, their findings are in accordance with neuropsychological theories that attribute a positive emotional tone to the left hemisphere and a negative tone to the right hemisphere (e.g., see review by Silberman and Weingartner, 1986). However, the results presented by Schiff and Lamon are based on an experimental procedure that is far from perfect. To begin with, the experimenters in the Schiff and Lamon studies were all familiar with the expected outcome. Furthermore, mood effects were inferred from verbalizations of subjects who performed unilateral contractions. Then, these verbalizations were evaluated by judges with criteria that were not specified. Thus, conclusions about the mood effects of unilateral contractions were, at best, based on inferential measures rather than direct observations. Using a procedure that avoided these methodological shortcomings, we recently made an attempt to validate the mood effects of unilateral contractions (Kop, Merckelbach and Muris, 1991). The results were disappointing: no evidence was found to suggest that negative mood effects and positive mood effects occur as a result of left and right muscle contraction, respectively. In their present commentary, Schiff and Lamon (this issue) cast doubts on the significance of this failure to replicate their findings. Their main argument is that our study did not follow the experimental setup employed by Schiff and Lamon (1989) and therefore did not provide a pure replication. In a strict sense, this is true of course. But, as stated before, their experimental procedure was far from perfect and, therefore, imitating such a procedure makes no sense. Apart from this fundamental issue, Schiff and Lamon raise three technical points about our study: the possible interference between stimulus material and mood, the order of unilateral contractions, and the stimulus material used. We will briefly comment on each point. As for the first point, in the Kop et al. study, subjects performed three successive left (LLL) and then three successive right (RRR) facial contractions, or vice versa. After each contraction, they were required to rate a cartoon on pleasantness. After three consecutive (LLL or RRR) contractions, mood measures were obtained. Schiff and Lamon argue that the cartoons might have interfered with the mood measures, thereby preventing an emotional effect of unilateral contraction. This, however, is very unlikely since subjects were familiar with the cartoons (subjects saw them during a pre-experimental baseline), the cartoons were emotionally neutral (see below), and they were presented in a counter-balanced fashion (which rules out any differential effect of the cartoons on mood). Note that by using the interference argument, Schiff and Lamon seem to acknowledge that the emotional effects of unilateral contraction are fragile, rather than "robust". This is remarkable because they also reported that three out of 12 subjects began to weep after left facial contraction, a finding that suggests that such manipulations have powerful Cortex, (1993) 29, 553-554
554
W.J. Kop and Others
effects (Schiff and Lamon, 1989, experiment I, p. 926). The order of muscle contraction in our study was LLLRRR (or RRRLLL). Schiff and Lamon (1989) used LRLR (or RLRL) in one of their studies. We fully agree with Schiff and Lamon that "there is no a priori reason for believing that the pattern of the sequence of contractions would influence the results". But, then it is argued by Schiff and Lamon that the salience of the emotional experience is enhanced through the contrast that is brought about by alternating left-right contractions. We are not in the position to evaluate the empirical basis of this claim. For the moment, we find this argument hardly convincing. Firstly, because the contrast of left-right contraction was absent in the third experiment described by Schiff and Lamon (i.e., a between-subject design was used), and emotional effects of unilateral contraction did nevertheless emerge. Secondly, every subject in the Kop et al. study did contract both sides of the face (i.e., a within-subject design was employed) and, hence each could, in principle, have experienced the contrast between left and right contractions. The third point advanced by Schiff and Lamon concerns the stimulus material that we used for documenting the effects of unilateral contractions. In our study, subjects rated a cartoon on pleasantness in the last 5 seconds during unilateral muscle contraction. Schiff and Lamon suspect that the use of a structured cartoon rather than an ambiguous stimulus can account for our failure to validate their results: the cartoon might itself have had an emotional effect that consequently overshadowed the effects of contractions. This suggestion is refuted by the data of our experiment. Before the experiment started (i.e., during the baseline period), the pleasantness of the cartoons was rated as rather moderate (mean= 5.5) on a visual analog scale (I= "I like this picture very much"; 10 = "I don't like this picture at all"). Thus, it seems fair to conclude that the cartoons were relatively neutral. In sum, we feel that the Kop et al. (1991) study represents an adequate attempt to replicate the findings previously reported by Schiff and Lamon. Why, then, was this study unable to demonstrate emotional effects of unilateral contractions? There are two possibilities. Firstly, Schiff and Lamon argue that they ruled out a motor-effort explanation in one of their experiments, by asking subjects which unilateral contraction they experienced as more difficult to perform. However, details about this part of their study are missing (e.g. when were the subjects asked?; was there a practice effect across trials?; what was the format of the answer categories? etc.). We therefore maintain that this point needs further clarification. Secondly, it is not unreasonable to suppose that the expectations of the experimenter play a role in the emotional consequences of unilateral contraction. In the Schiff and Lamon studies, the experimenters were familiar with the hypothesis to be tested. This was not the case in our experiment. To take this argument one step further, the Schiff and Lamon studies might be a subtle version of the famous Schachter and Singer experiment (Schachter and Singer, 1962). More specifically, asking subjects to pull back and lift one corner of the mouth for about 1 minute in front of an experimenter is an embarrassing, and therefore socially arousing task. Under this condition, the experimenter could shape the hedonic tone of the arousal by providing subtle positive or negative cues. Future studies should examine the plausibility of this explanation. Meanwhile, it remains to be seen whether the unilateral contraction effects reported by Schiff and Lamon need a neuropsychological interpretation. REFERENCES
H., and MuRIS, P. Unilateral contractions of facial muscles and emotion: a failed replication. Cortex, 27: 101-104, 1991. ScHACHTER, S., and SINGER, J. Cognitive, social, and physiological determinants of emotional state. Psychological Review, 69: 379-399, 1962. ScHIFF, B.B., and LAMON, M. Inducing emotion by unilateral contraction of facial muscles. Neuropsychologia, 27: 923-935, 1989. ScHIFF, B.B., and LAMON, M. Unilateral contraction of facial muscles do effect emotions: A "failed replication's" failure to perform a replication. Cortex, 1993 (this issue). SILBERMAN, E.K., and WEINGARTNER, H. Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5: 322-353, 1986. KoP, W.J., MERCKELBACH,
W.J. Kop, Department of Medical Psychology, University of Limburg, P.O. Box 616, 6200 MD. Maastricht, the Netherlands.