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Inducing Emotion by Unilateral Contraction of Hand Muscles
INDUCING EMOTION BY UNILATERAL CONTRACTION OF HAND MUSCLES Bernard B. Schiff and Mary Lamon! (Department of Psychology, University of Toronto)
Subjects who alternately contract the left and the right side of their face have emotional experiences that depend on the laterality of the contraction. Left side contractions result in sadness and right side contractions in a more positive state that is not readily characterized, but appears to be a mixture of feelings of well being and aggression (Schiff and Lamon, 1989). When these contractions are performed repeatedly on only one side of the face (either left or right), subjects fail to report these emotional experiences, but perception of an ambiguous picture (Schiff and Lamon, 1989), performance on a measure of social cognition (Schiff, Esses and Lamon, 1992) and perception of emotional expression in chimeric faces (Schiff and Truchon, 1994) are influenced in a manner which is consistent with the emotions that are reported when subjects alternate contractions. The sensory and motor connections of the facial muscles used in these contractions are with the contralateral cerebral hemisphere (Rinn, 1984). Right hemisphere activity is associated with negative affect and left hemisphere activity with positive affect (Davidson and Tomarken, 1989; Davidson, Ekman, Saron et aI., 1990; Silberman and Weingartner, 1986). Therefore, it was hypothesized that the emotional effects of unilateral contractions result from the spread of activation of the contralateral sensory and/or motor cortices to adjacent emotion relevant areas, in a manner consistent with Kinsbourne's cerebral distance hypothesis (Kinsbourne and Hicks, 1978). By this formulation unilateral contraction of any muscles with comparable sensory motor organization should be effective in inducing emotion. However, it is also possible that the arousal of emotions by unilateral contractions is uniquely a property of facial muscle. The importance of the face in the expression of emotion is well documented (Darwin, 1872; Ekman, 1989), and there is evidence that facial muscle activity contributes to the experience of emotion as well (Manstead, 1988; Strack, Martin and Stepper, 1988; Zajonc, Murphy and Inglehart, 1989). Therefore, it is plausible that there would be, with regard to the phenomenon described above, a special relationship between the face and the brain. The purpose of the research reported here was to investigate whether the induction of emotion by unilateral muscle contractions is restricted to the face. To do this we studied the effects of unilateral contraction of the muscles in the I
Presently at Huron College, University of Western Ontario, London, Ontario.
Cortex, (1994) 30, 247-254
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hand. The sensory and motor connections of the hand are with the contralateral hemisphere. Therefore, if the arousal of emotion by unilateral contractions is not specific to facial muscles the results of this experiment should parallel those found with the face. In this experiment we investigate the effects of unilateral contractions of the hand on the perception of three pictures from the Thematic Apperception Test (T.A.T.) (Bellak, 1986). These are the same pictures studied with facial muscle contractions (Schiff and Lamon, 1989). In the study of facial contractions we did not have a control group which told stories about these pictures without prior contractions. It was therefore not possible to conclude whether the differences between the stories following left and right contractions reflected the effects of one or the other of the contractions, or of both. To allow for an assessment of which contraction is effective a control contraction group is included in this experiment. MATERIALS AND METHOD
Subjects
Subjects were 57 right-handed male and female undergraduate volunteers who participated in order to receive course in an introductory psychology course. Subjects were assigned on an alternating basis to the right, left, and no contraction conditions. Design
The experiment employed a between-within subjects design. Hand contraction, right, left, or neither, was a between subjects, and picture type was a within subjects variable. The dependent measure was the proportion of negative, positive, and neutral propositions generated in the stories told about each of the three pictures. Materials
The experiment took place in a moderately lit room. The experimenter sat opposite the subject at a table with a tape recorder. Three T.A.T. pictures were used. Picture No. 13B is photograph with good resolution of a young boy sitting on the stoop of what looks like a farm house or a barn. Picture No. 14 is a silhouette of the back of a man standing at an open window. Picture No. 11 looks like a charcoal or pencil drawing. It is an ambiguous image which is difficult to decipher. Stories told about Picture 11 have been described as offering good clues regarding the mood of the subject, while stories about the other two pictures have been described as not being sensitive to emotional states (Bellak, 1986). The purpose of using all three pictures is to examine whether mood induced by unilateral contractions have similar effects to those which occur normally. The picture of primary interest therefore is Picture 11 which will be referred to as "the target". We expect that the other two pictures will not be sensitive to the effects of contractions (as was the case with facial contractions). '. Procedure
Subjects were told that the purpose of the experiment was to study the effects of muscular activity on perception. They signed consent forms in which they agreed to perform muscular contractions, and tell stories about three pictures, which stories would be recorded on tape for later analysis. They were then tested for handedness using a 6 item hand usage questionnaire (Porac and Cohen, 1981). A criterion of 5 out of 6 right handed responses
249
Emotion and contraction of hand muscles TABLE I
Number of Propositions Generated for Each Picture in Each Contraction Condition
Contraction condition Picture I Picture 2 Picture 3 Total
Right hand
Left hand
Control
Total
201 188 226 615
191 145 173 509
188 170 182 540
580 503 581
was used to include subjects in the experiment. Subjects in the left and right hand contraction conditions were instructed to squeeze as hard as they could on a sponge rubber ball (2.5// diameter). After 45 seconds they were told to relax. They repeated this four times with intervals of 10 to 15 seconds between each contraction. In the control, no contraction condition, subjects were seated and asked to wait while the experimenter busied herself for approximately one minute. Following this all subjects were told that they would be presented with three pictures. After each presentation they were to make up as dramatic a story as they could describing what they saw in the picture, what had led up to the events depicted in the picture, and what outcome was likely to ensue. The pictures were presented, one at a time, in a fixed order. Pictures 13B and 14 were shown first followed by picture 11, the target. Subjects viewed each picture for 45 seconds, returned it to the experimenter, told their story. The experimenter interacted with subjects only to encourage the more reticent story tellers to say more. This took the form of "is that all?", or "can you say moreT', or, when the subject omitted any of the three parts of the story (past, present or future), reminding them to include it. All stories were recorded on audio tape and then transcribed. Each story was divided into propositions, a proposition being defined as an idea unit loosely consisting of a topic and a comment on that topic. The order of propositions was randomized across conditions, pictures, and subjects. Two independent raters scored each proposition as positive, negative, or neutral in emotional tone. The raters agreed on more then 98% of the propositions. The disagreements were resolved by discussion.
RESULTS
The data of primary interest are the between group comparisons of the emotional tone of stories told in response to each picture. Before reporting those results we report more general characteristics of the data. Table I shows the absolute number of propositions generated for each picture for each hand contraction condition. Picture type affected the number of propositions generated. Analysis of variance revealed a significant main effect for picture type (F=4.77; d.f.=2, 108; p<.01; Mse=7.36). Subjects generated more propositions for pictures 1 and 3 than they did for picture 2 (t= 15.79, d.f. = 108, p<.001). Hand contraction condition did not affect the absolute number of propositions generated (F < 1; dJ. = 2, 54) nor was there evidence for an interaction between hand contraction condition and picture type (F< 1; dJ. = 4, 108). Because of differences in the absolute numbers of propositions among pictures, analyses of the emotional tone of the stories are reported in proportions of positive, neutral and negative propositions. The proportions of positive, neutral and negative propositions generated in
B.B. Schiff and M. Lamon
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Emotional Tone of Propositions Fig. 1 - The proportions of emotionally positive, negative and neutral propositions in stories told about pictures 1, 2 and 3 (the target picture) following contractions of the left hand, the right hand and in the control, no contraction condition.
response to each picture for each hand contraction condition are shown in Figure 1. Results for each picture, beginning with Picture 3, the target, are discussed separately. Hand contraction conditions differentially affected the emotional tone of stories told for Picture 3. An analysis of variance for negative propositions revealed a signif.icant effect of hand contraction condition (F = 4.65; dJ. = 2, 54; p<.05; Mse = .071). The left hand contraction condition produced a greater proportion of negative propositions than did the right hand condition and the control group (t=3.07; d.f.=54; p<.O l). Correspondingly, subjects in the left hand contraction condition produced a smaller proportion of positive propositions than did the right hand and control subjects (t=3.09; dJ.=54; p <.Ol). There were no differences between the control and the right hand contraction groups on any class of propositions.
Emotion and contraction of hand muscles
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While an analysis of variance did not yield significant results, planned comparisons of responses to Picture 1 provide some evidence about the emotional effects of right hand contractions. The right hand contraction condition generated proportionately fewer negative propositions than did the left hand contraction and the control group conditions (t = 3.07; d.f. = 54; p<.01). There were no between group differences in the proportions of positive propositions generated (F < 1; d.f. = 2. 54; Mse = .028). However, the right hand contraction group produced more neutral propositions than did the other two groups (t = 3.18; dJ. = 54; p< .OI). There were no differences between the left hand contraction and control groups for any class of propositions for Picture 1. There were no differences among groups for Picture 2 for any class of propositions. DISCUSSION
The results of this experiment are virtually identical to those reported following contractions of the face (Schiff and Lamon, 1989). Stories told about picture 3, the target, were more negative for the left contraction group than those told by the right contraction group, and the profile of negative and neutral propositions shown in Figure 1 is remarkably similar to that seen following facial contractions. Likewise, the absence of any effects on the stories told about picture 2 reported here is the same as was found with face contractions. It is only in the stories told about picture 1 that there is a difference between the two experiments. There were no effects on the stories told about picture 1 following face contractions, but there were following hand contractions. While we have no account of why this occurred the result is consistent with emotional effects already described. The stories which followed left hand contractions were more negative than those which followed right hand contractions. Therefore, it can be concluded that the emotional effects of unilateral muscle contractions are not restricted to facial musculature. However, we should not yet conclude categorically that the emotional effects of unilateral contractions are a general property of sensory-motor neurophysiology and will be demonstrable with all skeletal muscles. The hand, like the face though to a lesser degree, is involved in the expression of positive and negative emotions. People use their hands both to signal emotion and in emotional interactions. It is possible, then, that other muscles of the body, or configurations of muscle activity, which are less frequently associated with emotion will be less effective in inducing emotion. This remains to be resolved with further research. The second goal .pf this research was to identify the respective roles of the left and right side contractions in producing the differences between them. This was accomplished by comparing the stories which followed each contraction condition to those which followed a control, no contraction condition. For picture 3 there were no differences between the control condition and the right side contraction so the differences between left and right contractions are attributable entirely to the effects of the left side contraction. Following left side contractions the stories have more negative propositions and fewer positive pro-
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positions than in the other two conditions. However, for picture 1 it is the right contraction and not the left contraction which is effective in changing the stories from the control condition. Following right contractions the stories have fewer negative propositions and more neutral propositions. An explanation of this interaction between contraction condition and stimulus picture must be tentative because of the limited sample of pictures. However, it is possibile to suggest a post hoc account of this interaction on the basis of the distribution of propositions for pictures 1 and 3. Picture 1 has a high proportion of negative propositions (.48). This high level of negative responding to picture 1 may have masked the negative induction effects of left side contractions but have been optimal for manifesting the positive effects of the right contractions. Picture 3 on the other hand has roughly equal proportions of positive, negative and neutral propositions. The lower levels of negative responding to picture 3 may have allowed for the expression of the negative effects but it is possible that the positive effects of right side contractions are apparent only against the background of high levels of negative responding. Similar interactions between the effects of the contractions and baseline responding under control conditions have been observed in experiments on perceiver biases in face perception (Schiff and Truchon, 1994). The implications of these data for hemispheric specialization in emotion are consistent with existing views. The increase in negative tone following left side contractions is consistent with the activation of the negative properties of the contralateral right hemisphere. The decrease in the negative tone following right side contractions is likewise consistent with the positive functions attributed to the left hemisphere (Coffey, 1987; Davidson and Tomarken, 1989; Davidson et aI., 1990; Silberman and Weingartner, 1986). However, following right side contractions the stories had fewer negative propositions and more neutral but not more positive propositions. If right contractions induced positive affect, the failure to find more positive propositions could be explained by the image in picture 1. It is of a young boy sitting on a door stoop in a disconsolate manner. It is hard to translate this image into a positive story, so an increase in positive affect following right contractions might very well have reduced the negativity of the stories towards neutrality rather than positivity. However, an equally credible account of these data is that left hemisphere activation inhibits the right hemisphere (Heilman and Bowers, 1990; Rinn, 1984). This would explain the reduction of negative responses as well as the absence of increases in positive responses. This would also account for the absence of right contraction effects for picture 3 which did not elicit a high level of negative responding under control conditions. We did not systematically study the experience reported following unilateral hand contractions. However, in a pilot study using semic1inical procedures, as described in our earlier research (Schiff and Lamon, 1989), three of the five subjects tested reported experiences comparable to those which followed facial contractions. Subjects alternated between left (L.H.) and right (R.H.) contractions in a counterbalanced order. Representative reports for these subjects are as follows.
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Subject 1 L.H. "I felt teary in my eyes. It felt like being a sulking child." R.H. "I felt aggression, anger towards my brother. Lots of determination." Subject 2 L.H. "More sad than angry. I thought when you told me the clench my fist that I would feel angry, but I didn't. I felt sad. Mostly here (points to the areas around his eyes). I mean that it felt like I was getting teary, as if I could cry." R.H. "I can't put an emotional term to this. What I felt was that it was spreading here (points to area around the sides of his jaw). These muscles got very tight as if I was clenching my jaw." Subject 3 L.H. "Weird. Like a dead weight. Tension but not like it will go anywhere. A feeling of passivity. More shielded, defensive, a more inward sense. Fear of being attacked. A negative feeling." R.H. "More aggressive, like holding back a punch (makes a punching movement as she says this ... is generally activated). Strength and power with a desire to release. Feisty." Reports such as these depend on semiclinical procedures which encourage and allow the expression of feeling. They are therefore open to experimenter influence and must be considered with this reservation. However, phenomenological investigations of this kind may also provide insight into the phenomenon we have described and be useful in resolving such issues as whether right contraction effects are due to the arousal of positive emotions in the left hemisphere, or to left hemisphere inhibition of the right hemisphere. While details remain to be clarified, it is clear that unilateral contractions have effects that are consistent with activation of the contralateral hemispheres and arousal of their emotional properties. The effects have been found consistently in the responses to picture 3 which has been described in the T.A.T. as sensitive to the subjects' moods. They have not been found for picture 2, and not consistently found for picture 1 which have been described as not sensitive to the subjects' moods. Therefore the effects of the contractions have properties that are similar to moods which occur naturally. It should also be noticed that the effects of the contractions endure for at least three or four minutes. The stories about picture 3 are told after subjects have seen and told stories about the other two pictures. The duration of these effects have implications for the underlying neurology. ABSTRACT
Following 4 unilateral contractions of hand muscles, subjects told stories about pictures from the T.A.T. A propositional analysis of the stories showed that the emotional tone of stories told following left hand contractions were more negative than those told after right hand contractions. These results are comparable to those reported following unilateral facial contractions and are consistent with the arousal of the emotional properties of the hemisphere contralateral to the contractions. When the stories were compared to ones told in a control, no contraction condition, it was found that the differences between the left and right
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contractions were attributable to the effects of either one or the other depending on the control condition responses to the pictures. The results therefore provide evidence for both left and right hemisphere involvement in emotion. Acknowledgements. This research was supported by NSERC of Canada Grant OPGIN
012 to the first author.
REFERENCES BELLAK, L. The Thematic Apperception Test. Fourth Edition. Larchmont: Grune and Stratton, 1986. COFFEY, C.E. Cerebral laterality and emotion: The neurology of depression. Comprehensive Psychiatry, 28: 197-219, 1987. DARWIN, C. The Expression of Emotions in Animal and Man. London: John Murray, 1872. DAVIDSON, R.J., and TOMARKEN, AJ. In F. Boller and J. Grafman (Eds.), Handbook of Neuropsychology, Vol. 1. Amsterdam: Elsevier, 1989, pp. 419-441. DAVIDSON, R.J., EKMAN, P., SARON, C.D., SENULlS, J.A, and FRIESEN, W.V. Approach-withdrawal and cerebral asymmetry: emotional expression and brain physiology I. Journal of Personality and Social Psychology, 58: 330-341, 1990. EKMAN, P. In H. Wagner and A. Manstead (Eds.), Handbook of Psychophysiology: The Biological Psychology of Emotions and Social Processes. London: John Wiley, 1989, pp. 143-164. FERGUSON, G.A Statistical Analysis in Psychology and Education. New York: McGraw Hill, 1966. GAINOTII, G. In J. Gruzelier and P. Flor-Hemy (Eds.), Hemisyndromes: Psychobiology, Neurology, Psychiatry. Orlando: Academic Press, 1983, pp. 175-192. HEILMAN, K.M., and BOWERS, D. In N.L. Stein, B. Leventhal and T. Trabasso (Eds.), Psychological and Biological Approaches to Emotion. Hillsdale: Erlbaum, 1990, pp. 97-113. KINSBOURNE, M., and HICKS, R.E. In J. Requin (Ed.), Attention and Performance VII. Hillsdale: Erlbaum, 1978, pp. 345-362. MANSTEAD, A.S.R. In H.L. Wagner (Ed.), Social Psychophysiology: Theory and Clinical Applications. Chichester: Wiley, 1988, pp. 105-129. PORAC, c., and COREN, S. Lateral Preferences and Human Behavior. New York: Springer Verlag, 1981. RINN, W.E. The neuropsychology of facial expression: A review of the neurological and psychological mechanisms for producing facial expressions. Psychological Bulletin, 95: 52-77, 1984. SCHIFF, B.B., and LAMON, M. Inducing emotion by unilateral contraction of facial muscles: a new look at hemispheric specialization and the experience of emotion. Neuropsychologia, 27: 923-935, 1989. SCHIFF, B.B., ESSES, V.M., and LAMON, M. Unilateral facial contractions produce mood effects on social cognitive judgements. Cognition and Emotion, 6: 357-368, 1992. SCHIFF, B.B., and TRUCHON, C. Effect of unilateral contraction of hand muscles on perceiver biases in the perception of chimeric faces. Neuropsychologia (in press) 1994. SILBERMAN, E.K., and WEINGARTNER, H. Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5: 322-353, 1986. STRACK, F., MARTIN, L.L., and STEPPER, S. Inhibiting and facilitating conditions of the human smile: a nonobtrusive test of the facial feedback hypothesis. Journal of Personality and Social Psychology, 54: 768-777, 1988. ZAJONC, R.B., MURPHY, S.T., and INGLEHART, M. Feeling and facial efference: Implications of the vascular theory of emotion. Psychological Review, 96: 395-416, 1989. B.B.
Schiff. Department of Psychology, University of Toronto. Toronto, Ontario. Canada M5S
IAI.
Subjects who alternately contract the left and the right side of their face have emotional experiences that depend on the laterality of the contraction. Left side contractions result in sadness and right side contractions in a more positive state that is not readily characterized, but appears to be a mixture of feelings of well being and aggression (Schiff and Lamon, 1989). When these contractions are performed repeatedly on only one side of the face (either left or right), subjects fail to report these emotional experiences, but perception of an ambiguous picture (Schiff and Lamon, 1989), performance on a measure of social cognition (Schiff, Esses and Lamon, 1992) and perception of emotional expression in chimeric faces (Schiff and Truchon, 1994) are influenced in a manner which is consistent with the emotions that are reported when subjects alternate contractions. The sensory and motor connections of the facial muscles used in these contractions are with the contralateral cerebral hemisphere (Rinn, 1984). Right hemisphere activity is associated with negative affect and left hemisphere activity with positive affect (Davidson and Tomarken, 1989; Davidson, Ekman, Saron et aI., 1990; Silberman and Weingartner, 1986). Therefore, it was hypothesized that the emotional effects of unilateral contractions result from the spread of activation of the contralateral sensory and/or motor cortices to adjacent emotion relevant areas, in a manner consistent with Kinsbourne's cerebral distance hypothesis (Kinsbourne and Hicks, 1978). By this formulation unilateral contraction of any muscles with comparable sensory motor organization should be effective in inducing emotion. However, it is also possible that the arousal of emotions by unilateral contractions is uniquely a property of facial muscle. The importance of the face in the expression of emotion is well documented (Darwin, 1872; Ekman, 1989), and there is evidence that facial muscle activity contributes to the experience of emotion as well (Manstead, 1988; Strack, Martin and Stepper, 1988; Zajonc, Murphy and Inglehart, 1989). Therefore, it is plausible that there would be, with regard to the phenomenon described above, a special relationship between the face and the brain. The purpose of the research reported here was to investigate whether the induction of emotion by unilateral muscle contractions is restricted to the face. To do this we studied the effects of unilateral contraction of the muscles in the I
Presently at Huron College, University of Western Ontario, London, Ontario.
Cortex, (1994) 30, 247-254
248
B.B. Schiff and M. Lamon
hand. The sensory and motor connections of the hand are with the contralateral hemisphere. Therefore, if the arousal of emotion by unilateral contractions is not specific to facial muscles the results of this experiment should parallel those found with the face. In this experiment we investigate the effects of unilateral contractions of the hand on the perception of three pictures from the Thematic Apperception Test (T.A.T.) (Bellak, 1986). These are the same pictures studied with facial muscle contractions (Schiff and Lamon, 1989). In the study of facial contractions we did not have a control group which told stories about these pictures without prior contractions. It was therefore not possible to conclude whether the differences between the stories following left and right contractions reflected the effects of one or the other of the contractions, or of both. To allow for an assessment of which contraction is effective a control contraction group is included in this experiment. MATERIALS AND METHOD
Subjects
Subjects were 57 right-handed male and female undergraduate volunteers who participated in order to receive course in an introductory psychology course. Subjects were assigned on an alternating basis to the right, left, and no contraction conditions. Design
The experiment employed a between-within subjects design. Hand contraction, right, left, or neither, was a between subjects, and picture type was a within subjects variable. The dependent measure was the proportion of negative, positive, and neutral propositions generated in the stories told about each of the three pictures. Materials
The experiment took place in a moderately lit room. The experimenter sat opposite the subject at a table with a tape recorder. Three T.A.T. pictures were used. Picture No. 13B is photograph with good resolution of a young boy sitting on the stoop of what looks like a farm house or a barn. Picture No. 14 is a silhouette of the back of a man standing at an open window. Picture No. 11 looks like a charcoal or pencil drawing. It is an ambiguous image which is difficult to decipher. Stories told about Picture 11 have been described as offering good clues regarding the mood of the subject, while stories about the other two pictures have been described as not being sensitive to emotional states (Bellak, 1986). The purpose of using all three pictures is to examine whether mood induced by unilateral contractions have similar effects to those which occur normally. The picture of primary interest therefore is Picture 11 which will be referred to as "the target". We expect that the other two pictures will not be sensitive to the effects of contractions (as was the case with facial contractions). '. Procedure
Subjects were told that the purpose of the experiment was to study the effects of muscular activity on perception. They signed consent forms in which they agreed to perform muscular contractions, and tell stories about three pictures, which stories would be recorded on tape for later analysis. They were then tested for handedness using a 6 item hand usage questionnaire (Porac and Cohen, 1981). A criterion of 5 out of 6 right handed responses
249
Emotion and contraction of hand muscles TABLE I
Number of Propositions Generated for Each Picture in Each Contraction Condition
Contraction condition Picture I Picture 2 Picture 3 Total
Right hand
Left hand
Control
Total
201 188 226 615
191 145 173 509
188 170 182 540
580 503 581
was used to include subjects in the experiment. Subjects in the left and right hand contraction conditions were instructed to squeeze as hard as they could on a sponge rubber ball (2.5// diameter). After 45 seconds they were told to relax. They repeated this four times with intervals of 10 to 15 seconds between each contraction. In the control, no contraction condition, subjects were seated and asked to wait while the experimenter busied herself for approximately one minute. Following this all subjects were told that they would be presented with three pictures. After each presentation they were to make up as dramatic a story as they could describing what they saw in the picture, what had led up to the events depicted in the picture, and what outcome was likely to ensue. The pictures were presented, one at a time, in a fixed order. Pictures 13B and 14 were shown first followed by picture 11, the target. Subjects viewed each picture for 45 seconds, returned it to the experimenter, told their story. The experimenter interacted with subjects only to encourage the more reticent story tellers to say more. This took the form of "is that all?", or "can you say moreT', or, when the subject omitted any of the three parts of the story (past, present or future), reminding them to include it. All stories were recorded on audio tape and then transcribed. Each story was divided into propositions, a proposition being defined as an idea unit loosely consisting of a topic and a comment on that topic. The order of propositions was randomized across conditions, pictures, and subjects. Two independent raters scored each proposition as positive, negative, or neutral in emotional tone. The raters agreed on more then 98% of the propositions. The disagreements were resolved by discussion.
RESULTS
The data of primary interest are the between group comparisons of the emotional tone of stories told in response to each picture. Before reporting those results we report more general characteristics of the data. Table I shows the absolute number of propositions generated for each picture for each hand contraction condition. Picture type affected the number of propositions generated. Analysis of variance revealed a significant main effect for picture type (F=4.77; d.f.=2, 108; p<.01; Mse=7.36). Subjects generated more propositions for pictures 1 and 3 than they did for picture 2 (t= 15.79, d.f. = 108, p<.001). Hand contraction condition did not affect the absolute number of propositions generated (F < 1; dJ. = 2, 54) nor was there evidence for an interaction between hand contraction condition and picture type (F< 1; dJ. = 4, 108). Because of differences in the absolute numbers of propositions among pictures, analyses of the emotional tone of the stories are reported in proportions of positive, neutral and negative propositions. The proportions of positive, neutral and negative propositions generated in
B.B. Schiff and M. Lamon
250
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Emotional Tone of Propositions Fig. 1 - The proportions of emotionally positive, negative and neutral propositions in stories told about pictures 1, 2 and 3 (the target picture) following contractions of the left hand, the right hand and in the control, no contraction condition.
response to each picture for each hand contraction condition are shown in Figure 1. Results for each picture, beginning with Picture 3, the target, are discussed separately. Hand contraction conditions differentially affected the emotional tone of stories told for Picture 3. An analysis of variance for negative propositions revealed a signif.icant effect of hand contraction condition (F = 4.65; dJ. = 2, 54; p<.05; Mse = .071). The left hand contraction condition produced a greater proportion of negative propositions than did the right hand condition and the control group (t=3.07; d.f.=54; p<.O l). Correspondingly, subjects in the left hand contraction condition produced a smaller proportion of positive propositions than did the right hand and control subjects (t=3.09; dJ.=54; p <.Ol). There were no differences between the control and the right hand contraction groups on any class of propositions.
Emotion and contraction of hand muscles
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While an analysis of variance did not yield significant results, planned comparisons of responses to Picture 1 provide some evidence about the emotional effects of right hand contractions. The right hand contraction condition generated proportionately fewer negative propositions than did the left hand contraction and the control group conditions (t = 3.07; d.f. = 54; p<.01). There were no between group differences in the proportions of positive propositions generated (F < 1; d.f. = 2. 54; Mse = .028). However, the right hand contraction group produced more neutral propositions than did the other two groups (t = 3.18; dJ. = 54; p< .OI). There were no differences between the left hand contraction and control groups for any class of propositions for Picture 1. There were no differences among groups for Picture 2 for any class of propositions. DISCUSSION
The results of this experiment are virtually identical to those reported following contractions of the face (Schiff and Lamon, 1989). Stories told about picture 3, the target, were more negative for the left contraction group than those told by the right contraction group, and the profile of negative and neutral propositions shown in Figure 1 is remarkably similar to that seen following facial contractions. Likewise, the absence of any effects on the stories told about picture 2 reported here is the same as was found with face contractions. It is only in the stories told about picture 1 that there is a difference between the two experiments. There were no effects on the stories told about picture 1 following face contractions, but there were following hand contractions. While we have no account of why this occurred the result is consistent with emotional effects already described. The stories which followed left hand contractions were more negative than those which followed right hand contractions. Therefore, it can be concluded that the emotional effects of unilateral muscle contractions are not restricted to facial musculature. However, we should not yet conclude categorically that the emotional effects of unilateral contractions are a general property of sensory-motor neurophysiology and will be demonstrable with all skeletal muscles. The hand, like the face though to a lesser degree, is involved in the expression of positive and negative emotions. People use their hands both to signal emotion and in emotional interactions. It is possible, then, that other muscles of the body, or configurations of muscle activity, which are less frequently associated with emotion will be less effective in inducing emotion. This remains to be resolved with further research. The second goal .pf this research was to identify the respective roles of the left and right side contractions in producing the differences between them. This was accomplished by comparing the stories which followed each contraction condition to those which followed a control, no contraction condition. For picture 3 there were no differences between the control condition and the right side contraction so the differences between left and right contractions are attributable entirely to the effects of the left side contraction. Following left side contractions the stories have more negative propositions and fewer positive pro-
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positions than in the other two conditions. However, for picture 1 it is the right contraction and not the left contraction which is effective in changing the stories from the control condition. Following right contractions the stories have fewer negative propositions and more neutral propositions. An explanation of this interaction between contraction condition and stimulus picture must be tentative because of the limited sample of pictures. However, it is possibile to suggest a post hoc account of this interaction on the basis of the distribution of propositions for pictures 1 and 3. Picture 1 has a high proportion of negative propositions (.48). This high level of negative responding to picture 1 may have masked the negative induction effects of left side contractions but have been optimal for manifesting the positive effects of the right contractions. Picture 3 on the other hand has roughly equal proportions of positive, negative and neutral propositions. The lower levels of negative responding to picture 3 may have allowed for the expression of the negative effects but it is possible that the positive effects of right side contractions are apparent only against the background of high levels of negative responding. Similar interactions between the effects of the contractions and baseline responding under control conditions have been observed in experiments on perceiver biases in face perception (Schiff and Truchon, 1994). The implications of these data for hemispheric specialization in emotion are consistent with existing views. The increase in negative tone following left side contractions is consistent with the activation of the negative properties of the contralateral right hemisphere. The decrease in the negative tone following right side contractions is likewise consistent with the positive functions attributed to the left hemisphere (Coffey, 1987; Davidson and Tomarken, 1989; Davidson et aI., 1990; Silberman and Weingartner, 1986). However, following right side contractions the stories had fewer negative propositions and more neutral but not more positive propositions. If right contractions induced positive affect, the failure to find more positive propositions could be explained by the image in picture 1. It is of a young boy sitting on a door stoop in a disconsolate manner. It is hard to translate this image into a positive story, so an increase in positive affect following right contractions might very well have reduced the negativity of the stories towards neutrality rather than positivity. However, an equally credible account of these data is that left hemisphere activation inhibits the right hemisphere (Heilman and Bowers, 1990; Rinn, 1984). This would explain the reduction of negative responses as well as the absence of increases in positive responses. This would also account for the absence of right contraction effects for picture 3 which did not elicit a high level of negative responding under control conditions. We did not systematically study the experience reported following unilateral hand contractions. However, in a pilot study using semic1inical procedures, as described in our earlier research (Schiff and Lamon, 1989), three of the five subjects tested reported experiences comparable to those which followed facial contractions. Subjects alternated between left (L.H.) and right (R.H.) contractions in a counterbalanced order. Representative reports for these subjects are as follows.
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Subject 1 L.H. "I felt teary in my eyes. It felt like being a sulking child." R.H. "I felt aggression, anger towards my brother. Lots of determination." Subject 2 L.H. "More sad than angry. I thought when you told me the clench my fist that I would feel angry, but I didn't. I felt sad. Mostly here (points to the areas around his eyes). I mean that it felt like I was getting teary, as if I could cry." R.H. "I can't put an emotional term to this. What I felt was that it was spreading here (points to area around the sides of his jaw). These muscles got very tight as if I was clenching my jaw." Subject 3 L.H. "Weird. Like a dead weight. Tension but not like it will go anywhere. A feeling of passivity. More shielded, defensive, a more inward sense. Fear of being attacked. A negative feeling." R.H. "More aggressive, like holding back a punch (makes a punching movement as she says this ... is generally activated). Strength and power with a desire to release. Feisty." Reports such as these depend on semiclinical procedures which encourage and allow the expression of feeling. They are therefore open to experimenter influence and must be considered with this reservation. However, phenomenological investigations of this kind may also provide insight into the phenomenon we have described and be useful in resolving such issues as whether right contraction effects are due to the arousal of positive emotions in the left hemisphere, or to left hemisphere inhibition of the right hemisphere. While details remain to be clarified, it is clear that unilateral contractions have effects that are consistent with activation of the contralateral hemispheres and arousal of their emotional properties. The effects have been found consistently in the responses to picture 3 which has been described in the T.A.T. as sensitive to the subjects' moods. They have not been found for picture 2, and not consistently found for picture 1 which have been described as not sensitive to the subjects' moods. Therefore the effects of the contractions have properties that are similar to moods which occur naturally. It should also be noticed that the effects of the contractions endure for at least three or four minutes. The stories about picture 3 are told after subjects have seen and told stories about the other two pictures. The duration of these effects have implications for the underlying neurology. ABSTRACT
Following 4 unilateral contractions of hand muscles, subjects told stories about pictures from the T.A.T. A propositional analysis of the stories showed that the emotional tone of stories told following left hand contractions were more negative than those told after right hand contractions. These results are comparable to those reported following unilateral facial contractions and are consistent with the arousal of the emotional properties of the hemisphere contralateral to the contractions. When the stories were compared to ones told in a control, no contraction condition, it was found that the differences between the left and right
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contractions were attributable to the effects of either one or the other depending on the control condition responses to the pictures. The results therefore provide evidence for both left and right hemisphere involvement in emotion. Acknowledgements. This research was supported by NSERC of Canada Grant OPGIN
012 to the first author.
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Schiff. Department of Psychology, University of Toronto. Toronto, Ontario. Canada M5S
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