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Appetitive motivational influences on heart rate
person.
indiuid.
/IQ?
Vol.
4. No.
4. pp.
393-401,
1983
0191-x869:83
Printed in Great Britain. All rights reserved
APPETITIVE
$3 Out0
00
Copyright 81’ 1983 Pergamon PressLtd
MOTIVATIONAL HEART
INFLUENCES
ON
RATE
DON C. FOWLES Department
of Psychology,
The University
Of Iowa,
Iowa City, IA 52242, U.S.A
Summary-Seven experiments
employing monetary incentive (MI) vs performance feedback only (FO) m a continuous motor task demonstrated that heart rate (HR) responds to increases in appetitive motivation. In all experiments HR increases were greater with MI than with FO. Other findings include the following: I. A graded effect of MI (e.g. 04, 24, 54) on HR was found in two studies. 2. Motor response rates do not account for the HR differences. 3. Eliminating failure feedback does not diminish the effect of MI, suggesting that aversive motivation does not account for the results. 4. Consistent effects of MI over FO have been found with 50, 90 and lOOS< success conditions, but results with 10% success have been inconsistent. Fifty per cent yields somewhat smaller HR increases than 90%. but the differences are not significant. 5. A response cost paradigm in which subjects start with $6.00 and then lose SQ/failure feedback yielded results comparable to those for the standard reward paradigm. 6. Type A personality subjects showed a greater response to MI than did Type B subjects, suggesting greater appetitive motivation. Overall, these results suggest that HR may be used to assess excessive and deficient appetitive motivational responses which are central to numerous theories of personality and psychopathology.
INTRODUCTION
The hypothesis that heart rate (HR) responds to the incentive effects of rewards was put forth most clearly by Elliott (1969), who emphasized both the initiation of a response and the presence of an incentive. Incentive had to do with the importance of the situation for the subject. Unfortunately, this hypothesis has been largely neglected in recent years, quite possibly because a later review by Elliott (1974) emphasized the difficulty of demonstrating incentive effects which were not attributable to somatic activity. My own interest in the incentive hypothesis developed from the observation that a theory of motivation borrowed from Gray (1978, 1979) offered a new perspective on the HR literature. Specifically, the incentive effects on HR and Obrist’s (1976) recent work on active coping can be seen as reflecting appetitive motivational influences on HR (Fowles, 1980, 1982). In Gray’s theory. an appetitive motivational system activates behavior in both simple reward-seeking and activeavoidance situations. Thus, Elliott’s work with reward incentives represents the reward-seeking aspect of this system, whereas Obrist’s work on active coping (instrumental responding to avoid shock) represents the active-avoidance aspect. As will be noted later, this hypothesis that HR reflects hedonic processes associated with reward-seeking behavior is relevant to research on Type A behavior patterns, loss of interest in depression and anhedonia in schizophrenia.
METHODS
Because evidence for the reliability and quantitative importance of the incentive effect in humans is somewhat limited, my students and I have pursued a research program demonstrating an effect of monetary incentives (MI) on HR in college students. We have employed a continuous motor task, in which subjects press the button adjacent to whichever of 5 lights (arranged in a semicircle) is on, turning the light off. Another light comes on randomly when the subject presses a central button, and the task continues until the experimenter tells the subject to stop. In some studies we gave subjects different levels of success and failure feedback by manipulating task difficulty. Using the subject’s own performance and the amount of success we wished to produce, we established a time criterion for the rate of turning off lights. Subjects average about 80 responses (i.e. lights turned off) per minute, making success and failure feedback on every 393
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~OWLI’S
response unthinkable. As a practical matter, we give feedback (high-vs low-frequency tones) for blocks of five responses, and subjects are given instructions to this effect. In other studies there is no mention of success and failure or of any time criterion and only a single tone is employed, automatically following every fifth response. This practice avoids any threat of failure feedback and is comparable to a simple lOOo/, reward paradigm with animals. In each of the seven studies described below, the first trial was a practice trial without feedback. This trial yielded an estimate of the subject’s motor response rate and also served as a control trial for the effects of the task per se on HR. Although the statistical analyses employed analysis of covariance (ANCOVA) using Trial 1 HR as the covariate, the results presented in the figures below show change scores in which Trial 1 HR is subtracted from HR on later trials. All variables are between-subjects except the Trials factor.
RESULTS
Studies
I-3:
Demonstration
of Monetmy
incentive
(MI) Effects
In study 1 (Fowles, Fisher and Tranel, 1982), no Success feedback (10% vs 90%) and Incentive (feedback only vs 2ejsuccess) were the variables of interest (10 Ss/cell) and Trials served as a third factor, yielding a 2 x 2 x 4 ANCOVA design. The 3-min trials averaged around 48 feedbacks/trial. In the results for Trials 2-5 shown in Fig. 1, the Incentive main effect was significant (P < 0.02), but that for “/, Success was not, nor was the apparent interaction between these two variables (P > 0.10). The absence of this interaction was disappointing, since we had anticipated a larger On the cardiac acceleration for the 90% than the 10:; Success groups within the MI condition. other hand, the efficacy of MIS in promoting HR increases was in keeping with our theoretical prediction. To avoid leaving some of our Ss with a failure experience, we added a final trial in which the two 10% Success groups achieved 50% success, and we also gave the MI group 8$/success (they had earned only 404 or so in the previous 4 trials). As can be seen in Fig. 1, the change to SOO;, Success for the 10% Success/Feedback Only (FO) group had no effect on HR during Trial 6, but when associated with an incentive of 8$/success it produced a large increase in HR (% Success x Incentive, P < 0.05). Because some Ss in Study 1 complained of fatigue, the trials were shortened to 2 min each for later studies to avoid aversive stimulation. With this change in procedure, Study 2 (Fowles et al.,
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TRIALS
Fig. I. HR change relative to Trial 1 as a function of Incentive (04 vs 24) and ;6 Success (10 vs 9073. The lO%/MI group received 50% success and &/success on Trial 6. ____ = 24: ---- = 04. 0 = 90”; success; 0 = 10% success. From Fowles et al. (1982) Copyright ((_‘N1982, The Society for Psychophysiological Research. Reprinted with permission of the publisher.
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influences
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Fig. 2. HR change relative to Trial I as a function Incentive (04 vs 24). 0-O = 24; of q- --n = 04. From Fowles er al. (1982). Copyright 0 1982, The Society for Psychophysiological Research. Reprinted with permission of the publisher.
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TRIALS
Fig. 3. HR change relative to Trial I as a function of Magnitude of Incentive (04, 24, Se) and number of trials for which the incentive was given (2 vs 5 trials). The 2-trial groups received feedback only (i.e. 04) on Trials 66. 0 = 54; n = 24; 0 = 04. = 5 trials; --~ = 2 trials. From Tranel et al. (1982). Copyright 0 1982, The Society for Psychophysiological Research. Reprinted with permission of the publisher.
1982) was a simple comparison of a MI of 2$/success with FO, using 100% success for both groups (15 Ss/cell). As seen in Fig. 2, the effect of Incentive was significant (P < 0.025). In Study 3 (Fig. 3) Tranel, Fisher and Fowles (1982) employed 100% reinforcement with no mention of failure feedback to compare the effects of different magnitudes of incentive, contrasting the effects of SQ/success (54 for 5 trials) with 2Q/success (24 for 5 trials) and FO (04 for 5 trials). This study also investigated the effect of the S’s estimate of the total earnings for the experiment by telling some that they could earn money for Trials 2-6 (the 5-trail groups above) and others that they could do so only for Trials 2 and 3 (54 for 2 trials and 24 for 2 trials). The total earnings were, therefore, matched for the 54 group with two trials and the 24 group with 5 trials. Between Trials 2 and 3, Ss were told how many successes (FO groups) or how much money they had earned and what total earnings they could expect if they continued at the present rate of responding. Thus, they had the necessary information concerning their likely total earnings on Trial 3, and they may have had some intuitive estimate of this amount during Trial 2. The results were analyzed in three ways. First, the three groups (04, 24 and 54) receiving the same incentives during all 5 trials showed a strong main effect of MI (P < 0.001). Second, examining only Trials 2 and 3 for the four MI groups showed a main effect (P < 0.01) of Magnitude of Incentive (24 vs 54) but failed to find either a main effect or interaction for the Continue factor-the effect of knowing whether the incentives would continue for 2 vs 5 trials. Finally, as expected, changing from incentives on Trials 2 and 3 to FO on Trials 4-6 lowered HR for the two groups who had incentives discontinued relative to the groups receiving continued incentive (Continue/Discontinue x Time period, P < 0.05). Taking stock at this point, these studies established several important points. First, the reliability of the HR increase with MI’s is established, having been found in all three studies. Second, the graded HR response to the magnitude of incentive seems to rule out nonspecific factors and to indicate that the results are correctly attributed to the incentive value of the money per se. Third, the 514incentive in the third study produced a large effect: for example, the 5$/5-trial group, who averaged $8.29 for the session, showed a 10.2 bpm increase over the 0$/S-trial group and averaged 100.2 bpm during the 5 incentive trials. Fourth. anxiety concerning failure feedback was eliminated as a possible cause of the HR increases, since Study 3 instructed Ss only that they would hear a
396
DON C.
FOWLIS
tone after every fifth light and that they would receive money for each tone-i.e. the paradigm was, in effect, comparable to a simple operant conditioning paradigm with 100% reward and no mention of success or failure. Thus, the results are in keeping with the hypothesis stated above that HR is more closely associated with appetitive than with aversive motivational states. The history of psychological research on HR has been plagued by the problem of cardiac-somatic coupling. In order to attribute the HR results to an increase in appetitive motivation, it is necessary to preclude an explanation in terms of somatic activity with its associated metabolic demand. We have taken three approaches to this problem. The first approach was to introduce a predictable control task in which the lights move in a clockwise progression around the semicircle, thereby greatly speeding up the S’s instrumental responding on the task. Ss performing this task with neither feedback (i.e. no tones) nor MIS showed response rates in Studies 1 and 2 which were 4&45x faster than those seen in our experimental groups, yet manifested HRs equal to or lower than those of our FO groups (Fowles et al., 1982). In view of this result, HR does not appear to be very sensitive to differences in response rate per se in the absence of motivational differences. Secondly, the response-rate data were analyzed in a manner parallel to the analyses of HR. Neither a significant main effect of MI on response rate nor an interaction with other variables was seen in any of the studies, again indicating that response-rate data do not account for the HR results. Finally, correlational analyses between HR and response rate yielded no indication of cardiac-somatic coupling (Tranel et al.. 1982). Taken together, these results argue against attributing the incentive effects on HR to somatic activity. Studies 46:
Task D@culty
and Magnitude of Incentive
Although supporting the HR-incentive hypothesis. these studies did raise questions about the importance of two other parameters: y0 success (Task Difficulty) and total incentive for the experiment. A surprising lack of difference in the HR increase for the 10% and 9090 Success/MI groups was found in Study 1. Similarly, carefully informing Ss after Trial 2 in Study 3 as to their expected earnings for the entire experiment failed to produce a statistically significant effect of this knowledge on HR during Trials 2 and 3. The only finding was an effect of the Magnitude of Incentive at the time (i.e. on Trials 2 and 3). Consequently, these two parameters were the focus of the next three studies. In Study 4, Fisher (1982) examined the effect of Success feedback (10, 50, 90%) on HR in groups receiving either MI (3$/success) or FO. There were two questions of interest in this 3 x 2 design with 15 Ss/cell (and Trials as an additional, within-Ss factor). First, would providing feedback information after each trial&ensuring that Ss knew how many successes they had achieved and, when appropriate, how much money they had earned-prevent the HR increase in the 10% Success condition seen in Study l? That is, we suspected that some Ss may not have accurately tracked their success and may not have been fully aware of how poorly they were doing. We were also interested in the effects of Task Difficulty on the course of HR changes over trials. Obrist’s (1976) major finding with an active-avoidance paradigm was a more sustained HR elevation over trials with a ‘hard’ task, as compared with either very easy or impossible tasks. Our early incentive studies, in contrast, yielded only main effects of Incentives. Nevertheless, we had examined only extreme conditions (10, 90 and 100% success) and thought it possible that a 50% Task Difficulty might resemble Obrist’s ‘hard’ task and thus show a more sustained cardiac acceleration over trials, at least for the Ss receiving MIS. Neither of these hypotheses was clearly supported by the results of Fisher’s study (Fig. 4). The significant effects were a % Success x Incentive interaction (P < 0.05) and a y/, Success x Incentive x Trials interaction (P < 0.02). When analyzed separately to further examine these interactions, the MI groups showed only a main effect of y0 Success (P < 0.02), whereas the FO groups yielded only a % Success x Trials interaction (P < 0.05). A Duncan’s Multiple Range test for the MI groups showed that only the 10 and 90% groups differed. Thus the % Success x Incentive interaction could be attributed to a significant % Success effect for the MI groups but not for the FO groups, and the three-way interactive largely reflected the stability over trials of the 50% Success/F0 group compared with the decline for the other groups. This importance of the % Success variable for our MI groups fit our original expectations better than did the result of Study 1, but the different results for the two studies are hard to attribute
Appetitive
12
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motivational
m-m
90% MI
D-4 1-b
9O%FO 50%MI
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influences
on HR
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8-
90 % 6-
50%
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TRIALS TRIALS
Fig. 4. HR change relative to Trial I as a function of Incentive (04 vs 34) and o/0 Success (19, 50 and 90%). Adapted from Fisher (1982).
Fig. 5. HR change relative to Trial 1 as a function of Incentive (04 vs 34) and Y0 Success (50% vs 90%).
to the feedback information provided after each trial in Study 4. This additional feedback could not account for differences between the studies on Trial 2 (an increase from Trial 1 in Study 1, a decrease in Study 4) since the informational feedback was first provided after Trial 2. Unfortunately, we are not aware of any changes in our procedure prior to that point which could account for these results. Whatever the explanation, the results of Study 4 suggest that the tendency of incentives to promote HR increases can be counteracted if the % Success is low enough, though this conclusion is tentative until the reliability of the 10% Success group is established. Another point worth noting is that the 50 and 90% groups did not differ, indicating that variations in “/, Success in that range have, at most, a small effect. With respect to Obrist’s work, these findings with reward incentives clearly do not resemble his with a shock-avoidance paradigm: the 50% Success/MI group declined just as rapidly over trials as the other two MI groups. There was a sustained HR elevation for the 50% Success/F0 group, but this condition does not seem comparable to the high incentive, hard-task group in Obrist’s study. The result was, nevertheless, of sufficient interest to merit a second look. Study 5 exactly replicated the 50 and 90% groups from Study 4 in order to assess the reliability of both the Incentive effect on HR for the 50% groups and the flatness of the curve over trials for the 50% Success/F0 group. As presented in Fig. 5, the main effect of Incentive was significant (P < 0.05) but the effect of % Success was not and there were no interactions. The incentiveinduced HR increase at a 50% Success level did replicate, therefore, as did the failure of the small differences between 50 and 90% Success for the MI groups to reach significance. On the other hand, the flat HR response over trials for the 50% Success/F0 group in Study 4 was not replicated, eliminating any hint of an Obrist-like result with our appetitive paradigm. Consequently, the effects of Task Difficulty fail to interact with Trials in a simple reward-approach paradigm, although they appear to do so in Obrist’s active-avoidance paradigm with punishment. Other differences in procedure, of course, might possibly account for the differences in results*.g. the techniques for varying task difficulty differ from Obrist’s. In Study 6, Tranel(1982) again investigated the effect of total incentive for the experiment. Recall that in Study 3, there was no difference during Trials 2 and 3 between the groups receiving MIS only during those trials and the groups receiving money for Trials 2-6. This led us to conclude
that Magnitude of Incentive (the amount earned for each tone feedback) was a more powerful factor than the S’s perception of the total amount to be earned during the experiment. In a different approach to this question in Study 6, these factors were manipulated ~,itl~in (I /rid by varying the Density of Feedback-the number of lights to be turned off for each tone. That is, half the Ss were told that a ‘response unit’ was 5 lights, meaning that a tone would be presented every 5 lights, but the other half of the Ss were instructed that a ‘response unit’ was 20 lights and thus heard tones at only one-fourth the frequency of the 5-light Ss. As before, this feedback was presented without regard for speed, and there was no mention of success or failure. Magnitude of Incentive was also varied by a factor of 4, being either 2 or 84 per tone. The results presented in Fig. 6 are collapsed across another (irrelevant) factor with the result that there are 24 Ss,‘cell. This time there was a main effect of both Magnitude of Incentive (P < 0.01) and of Density of Feedback (P < 0.01). It appears in Fig. 6 that the total amount earned was the controlling factor, since the two groups earning the same amount of money (84/2O lights vs 24/5 lights) showed identical HR increases. Although it is unclear why 5’s in Study 3 did not respond to the total incentive for the experiment. the results of both studies are consistent with the appealingly simple hypothesis that the HR response is a function of the amount of incentive per work required. Stud),
7: Response
Cost und Tvpr A Pusomiit~
In the last study, Perkins (1982) substituted a response cost paradigm for our usual procedure and examined HR differences between Type A and Type B personalities. In the response cost paradigm rewards are taken away for poor performance, requiring the S to work to avoid this aversive event. Thus. there are many similarities to the active avoidance of shock. This change in our procedure offers a better approximation to Obrist’s active-coping paradigm than did the reward paradigms of Studies 4 and 5, while still retaining MIS as the reinforcer. As in Study 4, the question of whether the 50”/, Success group would be more stable over trials than the 10 and 90’;,, groups was of special interest. The Type A personality is of medical interest because it represents a risk factor for coronary heart disease (e.g. Friedman and Rosenman, 1959; Roseman. Brand, Sholtz and Friedman, 1976). Although a summary of the characteristics of this personality type is beyond the scope of the present paper, it can be asserted that the evidence suggests that Type A individuals exhibit sympathetic nervous system hyperresponsivity in the cardiovascular system and that they are
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TRIALS
Fig. 6. HR change relative to Trial 1 as a function of Magnitude of Incentive per feedback tone (24 v\ 84) and density of feedback tones (following every 5th light vs every 20th light). Adapted from Trancl (19X2).
Appetitive
motivational
influences
399
on HR
behaviorally highly ‘active’. From the perspective of the motivational theory under discussion here, this combination of features suggests that a strong appetitive motivational system response might contribute to the etiology of Type A behavior. This reasoning led Perkins to examine the HR reaction of Type A vs Type B Ss in the response cost paradigm. The factors in this study were Incentive (54 vs O$), Personality (Type A vs Type B), % Success (10, 50, 90) and Trials (2-5bi.e. a 2 x 2 x 3 x 4 ANCOVA-with 10 Ss/cell. The MI groups received $6 at the beginning of Trial 2 and were told that each failure tone as a result of slow performance represented a loss of 54. The FO Ss were told that, in order to make the task more interesting, they began with 600 points and would lose 5 points for each failure tone. The results for Incentive and % Success are presented in Fig. 7 (collapsed across Personality and hence with 20 Ss/cell). The main effect of Incentive was significant (P < 0.01) and there was a trend toward an Incentive x % Success interaction (P < 0.10). The similarity of the results to Studies 4 and 5 suggests that employing a response cost paradigm did not alter the HR response. The absence of an interaction with Trials indicated again that the 50% Success group did not respond like Obrist’s ‘hard’-task group. The 50 and 90% groups resembled, within the limits of sampling fluctuation, those of Studies 4 and 5. The only large discrepancy was found in the problematic 10% Success/MI group, which showed a slightly greater HR increase than the FO groups in Perkins’ study, in contrast to a smaller response (actually, a decline) in Fisher’s study. With respect to the Type A factor (Fig. 8), there was a main effect of Personality (P < 0.001): Type A Ss showed a greater increase in HR to the feedback conditions (regardless of Incentives or % Success) than did Type Bs. A Personality x Incentive interaction (P < 0.05) reflected the greater efficacy of MI in producing differences between Type As and Type Bs. Although there was an interaction involving Personality x % Success x Trials (P < 0.05) it is probably uninterpretable. In summary, Type A Ss respond more strongly than Type Bs to the introduction of performance feedback, and this difference between Type As and Type Bs appears to be greater with MIS. Although these results require replication and extension to the simple reward paradigm, they are compatible with the intitial hypothesis that differences in an appetitive motivational system Putting this another way, insofar as the theory that contribute to the Type A/B distinction. appetitive motivational influences are largely responsible for psychological effects on HR is supported by the studies reported here, Perkins’ results offer a new perspective on Type A behavior.
2
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Fig. 7. HR change relative to Trial I as a function of Incentive (04 vs 54) and y0 Success (10, 50 and 90%) in a response cost paradigm. Adapted from Perkins (1982).
3
4
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TRIALS
TRIALS
Fig. 8. HR change of Incentive (04 vs Type B behavior) Adapted
relative to Trial 1 as a function 54) and Personality (Type A vs in a response cost paradigm. from Perkins (1983).
400
D. C. FOWLES
COMMENT
ON
THE
HR
STUDIES
These studies strongly support the hypothesis that appetitive motivation has an important effect on HR, apparently not attributable to cardiac-somatic coupling. The incentive effect on HR has been obtained in all of the seven studies considered here and, when examined, has shown a response proportional to the magnitude of incentive. It does not appear that aversive motivation associated with failure feedback or frustrative nonreward contributes to this effect, since the HR response is at least as large in the absence of evaluative feedback as when subjects receive some failure feedback (e.g. 90% success). Assuming that cardiac-somatic coupling and frustrative nonreward can be rejected as explanations for the incentive effect on HR, the appetitive hypothesis must be accepted and awarded full status as a psychological influence on HR. Perkins’ study has already demonstrated one application to the study of personality-the Type A behavior pattern. Whereas most studies in this area have focused on stress and aversive motivation with little theoretical development, his study was unusual in employing procedures developed for a specific theoretical appproach and in emphasizing appetitive motivation. The same approach might be fruitfully applied to other personality constructs which emphasize strong reward-seeking behavior+.g. impulsivity, some characteristics of extraversion and perhaps psychopathy. Where strong reward-seeking behavior is concerned, it is difficult at the behavioral level to choose between excessive appetitive motivation (sensitivity to rewards) and deficient inhibitory mechanisms (insensitivity to punishments and frustrative nonreward). It is hoped that evaluation of cardiac acceleration in response to rewards will indicate whether or not excessive appetitive motivation is present. More directly, there are two well-known theories of psychopathology which postulate a deficiency of hedonic motivation. One of the key symptoms of depression is ‘loss of interest’, and this symptom is particularly associated with autonomous or endogenous (Fowles and Gersh, 1979) or endogenomorphic (Klein, 1974) depression. This loss of interest has been attributed to loss of reinforcer effectiveness (e.g. Costello, 1972; Klein, 1974). If the cardiac response to incentives should distinguish between patients with a dysfunctional appetitive motivational system (i.e. who are unresponsive to all rewards) and those whose depression is more reactive to current environmental events (i.e. who do respond to rewards if present), it will be a valuable subtyping procedure. In a similar vein, clinical folklore has long employed the term anhedonia to describe some schizophrenics, especially socially-withdrawn schizophrenics (Depue, 1976). Whereas the loss of appetitive motivation in depression is more transient, the schizophrenic’s anhedonia is typically viewed as a trait, one undoubtedly contributing to the chronic poor adjustment seen in these patients. Although it seems likely that incentives other than money may be required for research with acutely-disturbed psychiatric patients, the present paradigm may be valuable for clinicallyrelated research with college students. For example, the development of an anhedonia scale for use with college students (Chapman, Chapman and Raulin, 1976) makes it possible to investigate the relationship between HR and anhedonia in college populations. REFERENCES Chapman L. J., Chapman J. P. and Raulin M. L. (1976) Scales for physical and social anhedonia. J. ahnorm. Psycho/. 85, 376382. Costello C. G. (1972) Depression: loss of reinforcer or loss of reinforcer effectiveness. Behav. Ther. 3, 24G247. Depue R. A. (1976) An activity-withdrawal distinction in schizophrenia: behavioral, clinical, brain damage, and neurophysiological correlates. J. abnorm. Psychol. 85, 174185. Elliott R. (I 969) Tonic heart rate: experiments on the effects of collative variables lead to a hypothesis about its motivational significance. J. Person. sot. Psycho/. 12, 21 l-228. Elliott R. (1974) The motivational significance of heart rate. In Cardiovascular Psychophysiology: Current Issues in Response Mechanisms, Biofeedback, and Methodology (Edited by Obrist P. A., Black A. H., Brener J. and DiCara L. V.). Aldine, Chicago, Ill. Fisher A. E. (1982) The effects of differing levels of incentive on human heart rate. Unpublished Master’s Thesis, University of Iowa, la. Fowles D. C. (1980) The three arousal model: implications of Gray’s two-factor learning theory for heart rate, electrodermal activity, and psychopathy. Psychophysiology 17, 87-104. Fowles D. C. (1982) Heart rate as an index of anxiety: failure of a hypothesis. In Focus on Cardiovascular Psychophysiology (Edited by Cacioppo J. T. and Petty R. E.). Guilford Press, New York.
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Fowles and Gersh F. (1979) Neurotic depression-I. The endogenous-neurotic distinction. In The Psychobiology of the Depressive Disorders: Implicationsfor the Effects of Stress (Edited by Depue R. A.). Academic Press, New York. Fowles D. C., Fisher A. E. and Tranel D. T. (1982) The heart beats to reward: the effect of monetary incentive on heart rate. Psychophysiology 19, 506-5 14. Friedman M. and Rosenman R. H. (1959) Association of specific overt behavior pattern with blood and cardiovascular finding. J. Am. med. Ass. 169, 12861296. Gray J. A. (1978) The neuropsychology of anxiety. Br. J. Psychol. 69, 417-434. Gray J. A. (1979) A neuropsychological theory of anxiety. In Emotions in Personality and Psychopathology (Edited by Izard C. E.). Plenum Press, New York. Klein D. F. (1974) Endogenomorphic depression: a conceptual and terminological revision. Archs gen. Psychiat. 31, 447454. Obrist P. A. (1976) The cardiovascular-behavioral interaction-As it appears today. Psychophysiology 13, 95-107. Perkins K. A. (1982) Heart rate change in Type A and Type B males as a function of incentive and level of task difficulty in a response cost paradigm. Unpublished Doctoral Dissertation, University of Iowa, Ia. Rosenman R. H., Brand R. J., Sholtz R. 1. and Friedman M. (1976) Multivariate prediction of coronary heart disease during 8.5-year follow-up in the W. Collaborative Group Study. Am. J. Cardiol. 37, 902-910. Tranel D. T. (1982) Human heart rate and electrodermal response as a function of monetarv incentive and frustrative nonreward. Unpublished Doctoral Dissertation, University of Iowa, Ia. Tranel D. T., Fisher A. E. and Fowles D. C. (1982) Magnitude of incentive effects on heart rate. Psychophysiology 19, 514-519.
indiuid.
/IQ?
Vol.
4. No.
4. pp.
393-401,
1983
0191-x869:83
Printed in Great Britain. All rights reserved
APPETITIVE
$3 Out0
00
Copyright 81’ 1983 Pergamon PressLtd
MOTIVATIONAL HEART
INFLUENCES
ON
RATE
DON C. FOWLES Department
of Psychology,
The University
Of Iowa,
Iowa City, IA 52242, U.S.A
Summary-Seven experiments
employing monetary incentive (MI) vs performance feedback only (FO) m a continuous motor task demonstrated that heart rate (HR) responds to increases in appetitive motivation. In all experiments HR increases were greater with MI than with FO. Other findings include the following: I. A graded effect of MI (e.g. 04, 24, 54) on HR was found in two studies. 2. Motor response rates do not account for the HR differences. 3. Eliminating failure feedback does not diminish the effect of MI, suggesting that aversive motivation does not account for the results. 4. Consistent effects of MI over FO have been found with 50, 90 and lOOS< success conditions, but results with 10% success have been inconsistent. Fifty per cent yields somewhat smaller HR increases than 90%. but the differences are not significant. 5. A response cost paradigm in which subjects start with $6.00 and then lose SQ/failure feedback yielded results comparable to those for the standard reward paradigm. 6. Type A personality subjects showed a greater response to MI than did Type B subjects, suggesting greater appetitive motivation. Overall, these results suggest that HR may be used to assess excessive and deficient appetitive motivational responses which are central to numerous theories of personality and psychopathology.
INTRODUCTION
The hypothesis that heart rate (HR) responds to the incentive effects of rewards was put forth most clearly by Elliott (1969), who emphasized both the initiation of a response and the presence of an incentive. Incentive had to do with the importance of the situation for the subject. Unfortunately, this hypothesis has been largely neglected in recent years, quite possibly because a later review by Elliott (1974) emphasized the difficulty of demonstrating incentive effects which were not attributable to somatic activity. My own interest in the incentive hypothesis developed from the observation that a theory of motivation borrowed from Gray (1978, 1979) offered a new perspective on the HR literature. Specifically, the incentive effects on HR and Obrist’s (1976) recent work on active coping can be seen as reflecting appetitive motivational influences on HR (Fowles, 1980, 1982). In Gray’s theory. an appetitive motivational system activates behavior in both simple reward-seeking and activeavoidance situations. Thus, Elliott’s work with reward incentives represents the reward-seeking aspect of this system, whereas Obrist’s work on active coping (instrumental responding to avoid shock) represents the active-avoidance aspect. As will be noted later, this hypothesis that HR reflects hedonic processes associated with reward-seeking behavior is relevant to research on Type A behavior patterns, loss of interest in depression and anhedonia in schizophrenia.
METHODS
Because evidence for the reliability and quantitative importance of the incentive effect in humans is somewhat limited, my students and I have pursued a research program demonstrating an effect of monetary incentives (MI) on HR in college students. We have employed a continuous motor task, in which subjects press the button adjacent to whichever of 5 lights (arranged in a semicircle) is on, turning the light off. Another light comes on randomly when the subject presses a central button, and the task continues until the experimenter tells the subject to stop. In some studies we gave subjects different levels of success and failure feedback by manipulating task difficulty. Using the subject’s own performance and the amount of success we wished to produce, we established a time criterion for the rate of turning off lights. Subjects average about 80 responses (i.e. lights turned off) per minute, making success and failure feedback on every 393
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response unthinkable. As a practical matter, we give feedback (high-vs low-frequency tones) for blocks of five responses, and subjects are given instructions to this effect. In other studies there is no mention of success and failure or of any time criterion and only a single tone is employed, automatically following every fifth response. This practice avoids any threat of failure feedback and is comparable to a simple lOOo/, reward paradigm with animals. In each of the seven studies described below, the first trial was a practice trial without feedback. This trial yielded an estimate of the subject’s motor response rate and also served as a control trial for the effects of the task per se on HR. Although the statistical analyses employed analysis of covariance (ANCOVA) using Trial 1 HR as the covariate, the results presented in the figures below show change scores in which Trial 1 HR is subtracted from HR on later trials. All variables are between-subjects except the Trials factor.
RESULTS
Studies
I-3:
Demonstration
of Monetmy
incentive
(MI) Effects
In study 1 (Fowles, Fisher and Tranel, 1982), no Success feedback (10% vs 90%) and Incentive (feedback only vs 2ejsuccess) were the variables of interest (10 Ss/cell) and Trials served as a third factor, yielding a 2 x 2 x 4 ANCOVA design. The 3-min trials averaged around 48 feedbacks/trial. In the results for Trials 2-5 shown in Fig. 1, the Incentive main effect was significant (P < 0.02), but that for “/, Success was not, nor was the apparent interaction between these two variables (P > 0.10). The absence of this interaction was disappointing, since we had anticipated a larger On the cardiac acceleration for the 90% than the 10:; Success groups within the MI condition. other hand, the efficacy of MIS in promoting HR increases was in keeping with our theoretical prediction. To avoid leaving some of our Ss with a failure experience, we added a final trial in which the two 10% Success groups achieved 50% success, and we also gave the MI group 8$/success (they had earned only 404 or so in the previous 4 trials). As can be seen in Fig. 1, the change to SOO;, Success for the 10% Success/Feedback Only (FO) group had no effect on HR during Trial 6, but when associated with an incentive of 8$/success it produced a large increase in HR (% Success x Incentive, P < 0.05). Because some Ss in Study 1 complained of fatigue, the trials were shortened to 2 min each for later studies to avoid aversive stimulation. With this change in procedure, Study 2 (Fowles et al.,
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Fig. I. HR change relative to Trial 1 as a function of Incentive (04 vs 24) and ;6 Success (10 vs 9073. The lO%/MI group received 50% success and &/success on Trial 6. ____ = 24: ---- = 04. 0 = 90”; success; 0 = 10% success. From Fowles et al. (1982) Copyright ((_‘N1982, The Society for Psychophysiological Research. Reprinted with permission of the publisher.
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Fig. 3. HR change relative to Trial I as a function of Magnitude of Incentive (04, 24, Se) and number of trials for which the incentive was given (2 vs 5 trials). The 2-trial groups received feedback only (i.e. 04) on Trials 66. 0 = 54; n = 24; 0 = 04. = 5 trials; --~ = 2 trials. From Tranel et al. (1982). Copyright 0 1982, The Society for Psychophysiological Research. Reprinted with permission of the publisher.
1982) was a simple comparison of a MI of 2$/success with FO, using 100% success for both groups (15 Ss/cell). As seen in Fig. 2, the effect of Incentive was significant (P < 0.025). In Study 3 (Fig. 3) Tranel, Fisher and Fowles (1982) employed 100% reinforcement with no mention of failure feedback to compare the effects of different magnitudes of incentive, contrasting the effects of SQ/success (54 for 5 trials) with 2Q/success (24 for 5 trials) and FO (04 for 5 trials). This study also investigated the effect of the S’s estimate of the total earnings for the experiment by telling some that they could earn money for Trials 2-6 (the 5-trail groups above) and others that they could do so only for Trials 2 and 3 (54 for 2 trials and 24 for 2 trials). The total earnings were, therefore, matched for the 54 group with two trials and the 24 group with 5 trials. Between Trials 2 and 3, Ss were told how many successes (FO groups) or how much money they had earned and what total earnings they could expect if they continued at the present rate of responding. Thus, they had the necessary information concerning their likely total earnings on Trial 3, and they may have had some intuitive estimate of this amount during Trial 2. The results were analyzed in three ways. First, the three groups (04, 24 and 54) receiving the same incentives during all 5 trials showed a strong main effect of MI (P < 0.001). Second, examining only Trials 2 and 3 for the four MI groups showed a main effect (P < 0.01) of Magnitude of Incentive (24 vs 54) but failed to find either a main effect or interaction for the Continue factor-the effect of knowing whether the incentives would continue for 2 vs 5 trials. Finally, as expected, changing from incentives on Trials 2 and 3 to FO on Trials 4-6 lowered HR for the two groups who had incentives discontinued relative to the groups receiving continued incentive (Continue/Discontinue x Time period, P < 0.05). Taking stock at this point, these studies established several important points. First, the reliability of the HR increase with MI’s is established, having been found in all three studies. Second, the graded HR response to the magnitude of incentive seems to rule out nonspecific factors and to indicate that the results are correctly attributed to the incentive value of the money per se. Third, the 514incentive in the third study produced a large effect: for example, the 5$/5-trial group, who averaged $8.29 for the session, showed a 10.2 bpm increase over the 0$/S-trial group and averaged 100.2 bpm during the 5 incentive trials. Fourth. anxiety concerning failure feedback was eliminated as a possible cause of the HR increases, since Study 3 instructed Ss only that they would hear a
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tone after every fifth light and that they would receive money for each tone-i.e. the paradigm was, in effect, comparable to a simple operant conditioning paradigm with 100% reward and no mention of success or failure. Thus, the results are in keeping with the hypothesis stated above that HR is more closely associated with appetitive than with aversive motivational states. The history of psychological research on HR has been plagued by the problem of cardiac-somatic coupling. In order to attribute the HR results to an increase in appetitive motivation, it is necessary to preclude an explanation in terms of somatic activity with its associated metabolic demand. We have taken three approaches to this problem. The first approach was to introduce a predictable control task in which the lights move in a clockwise progression around the semicircle, thereby greatly speeding up the S’s instrumental responding on the task. Ss performing this task with neither feedback (i.e. no tones) nor MIS showed response rates in Studies 1 and 2 which were 4&45x faster than those seen in our experimental groups, yet manifested HRs equal to or lower than those of our FO groups (Fowles et al., 1982). In view of this result, HR does not appear to be very sensitive to differences in response rate per se in the absence of motivational differences. Secondly, the response-rate data were analyzed in a manner parallel to the analyses of HR. Neither a significant main effect of MI on response rate nor an interaction with other variables was seen in any of the studies, again indicating that response-rate data do not account for the HR results. Finally, correlational analyses between HR and response rate yielded no indication of cardiac-somatic coupling (Tranel et al.. 1982). Taken together, these results argue against attributing the incentive effects on HR to somatic activity. Studies 46:
Task D@culty
and Magnitude of Incentive
Although supporting the HR-incentive hypothesis. these studies did raise questions about the importance of two other parameters: y0 success (Task Difficulty) and total incentive for the experiment. A surprising lack of difference in the HR increase for the 10% and 9090 Success/MI groups was found in Study 1. Similarly, carefully informing Ss after Trial 2 in Study 3 as to their expected earnings for the entire experiment failed to produce a statistically significant effect of this knowledge on HR during Trials 2 and 3. The only finding was an effect of the Magnitude of Incentive at the time (i.e. on Trials 2 and 3). Consequently, these two parameters were the focus of the next three studies. In Study 4, Fisher (1982) examined the effect of Success feedback (10, 50, 90%) on HR in groups receiving either MI (3$/success) or FO. There were two questions of interest in this 3 x 2 design with 15 Ss/cell (and Trials as an additional, within-Ss factor). First, would providing feedback information after each trial&ensuring that Ss knew how many successes they had achieved and, when appropriate, how much money they had earned-prevent the HR increase in the 10% Success condition seen in Study l? That is, we suspected that some Ss may not have accurately tracked their success and may not have been fully aware of how poorly they were doing. We were also interested in the effects of Task Difficulty on the course of HR changes over trials. Obrist’s (1976) major finding with an active-avoidance paradigm was a more sustained HR elevation over trials with a ‘hard’ task, as compared with either very easy or impossible tasks. Our early incentive studies, in contrast, yielded only main effects of Incentives. Nevertheless, we had examined only extreme conditions (10, 90 and 100% success) and thought it possible that a 50% Task Difficulty might resemble Obrist’s ‘hard’ task and thus show a more sustained cardiac acceleration over trials, at least for the Ss receiving MIS. Neither of these hypotheses was clearly supported by the results of Fisher’s study (Fig. 4). The significant effects were a % Success x Incentive interaction (P < 0.05) and a y/, Success x Incentive x Trials interaction (P < 0.02). When analyzed separately to further examine these interactions, the MI groups showed only a main effect of y0 Success (P < 0.02), whereas the FO groups yielded only a % Success x Trials interaction (P < 0.05). A Duncan’s Multiple Range test for the MI groups showed that only the 10 and 90% groups differed. Thus the % Success x Incentive interaction could be attributed to a significant % Success effect for the MI groups but not for the FO groups, and the three-way interactive largely reflected the stability over trials of the 50% Success/F0 group compared with the decline for the other groups. This importance of the % Success variable for our MI groups fit our original expectations better than did the result of Study 1, but the different results for the two studies are hard to attribute
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Fig. 5. HR change relative to Trial 1 as a function of Incentive (04 vs 34) and Y0 Success (50% vs 90%).
to the feedback information provided after each trial in Study 4. This additional feedback could not account for differences between the studies on Trial 2 (an increase from Trial 1 in Study 1, a decrease in Study 4) since the informational feedback was first provided after Trial 2. Unfortunately, we are not aware of any changes in our procedure prior to that point which could account for these results. Whatever the explanation, the results of Study 4 suggest that the tendency of incentives to promote HR increases can be counteracted if the % Success is low enough, though this conclusion is tentative until the reliability of the 10% Success group is established. Another point worth noting is that the 50 and 90% groups did not differ, indicating that variations in “/, Success in that range have, at most, a small effect. With respect to Obrist’s work, these findings with reward incentives clearly do not resemble his with a shock-avoidance paradigm: the 50% Success/MI group declined just as rapidly over trials as the other two MI groups. There was a sustained HR elevation for the 50% Success/F0 group, but this condition does not seem comparable to the high incentive, hard-task group in Obrist’s study. The result was, nevertheless, of sufficient interest to merit a second look. Study 5 exactly replicated the 50 and 90% groups from Study 4 in order to assess the reliability of both the Incentive effect on HR for the 50% groups and the flatness of the curve over trials for the 50% Success/F0 group. As presented in Fig. 5, the main effect of Incentive was significant (P < 0.05) but the effect of % Success was not and there were no interactions. The incentiveinduced HR increase at a 50% Success level did replicate, therefore, as did the failure of the small differences between 50 and 90% Success for the MI groups to reach significance. On the other hand, the flat HR response over trials for the 50% Success/F0 group in Study 4 was not replicated, eliminating any hint of an Obrist-like result with our appetitive paradigm. Consequently, the effects of Task Difficulty fail to interact with Trials in a simple reward-approach paradigm, although they appear to do so in Obrist’s active-avoidance paradigm with punishment. Other differences in procedure, of course, might possibly account for the differences in results*.g. the techniques for varying task difficulty differ from Obrist’s. In Study 6, Tranel(1982) again investigated the effect of total incentive for the experiment. Recall that in Study 3, there was no difference during Trials 2 and 3 between the groups receiving MIS only during those trials and the groups receiving money for Trials 2-6. This led us to conclude
that Magnitude of Incentive (the amount earned for each tone feedback) was a more powerful factor than the S’s perception of the total amount to be earned during the experiment. In a different approach to this question in Study 6, these factors were manipulated ~,itl~in (I /rid by varying the Density of Feedback-the number of lights to be turned off for each tone. That is, half the Ss were told that a ‘response unit’ was 5 lights, meaning that a tone would be presented every 5 lights, but the other half of the Ss were instructed that a ‘response unit’ was 20 lights and thus heard tones at only one-fourth the frequency of the 5-light Ss. As before, this feedback was presented without regard for speed, and there was no mention of success or failure. Magnitude of Incentive was also varied by a factor of 4, being either 2 or 84 per tone. The results presented in Fig. 6 are collapsed across another (irrelevant) factor with the result that there are 24 Ss,‘cell. This time there was a main effect of both Magnitude of Incentive (P < 0.01) and of Density of Feedback (P < 0.01). It appears in Fig. 6 that the total amount earned was the controlling factor, since the two groups earning the same amount of money (84/2O lights vs 24/5 lights) showed identical HR increases. Although it is unclear why 5’s in Study 3 did not respond to the total incentive for the experiment. the results of both studies are consistent with the appealingly simple hypothesis that the HR response is a function of the amount of incentive per work required. Stud),
7: Response
Cost und Tvpr A Pusomiit~
In the last study, Perkins (1982) substituted a response cost paradigm for our usual procedure and examined HR differences between Type A and Type B personalities. In the response cost paradigm rewards are taken away for poor performance, requiring the S to work to avoid this aversive event. Thus. there are many similarities to the active avoidance of shock. This change in our procedure offers a better approximation to Obrist’s active-coping paradigm than did the reward paradigms of Studies 4 and 5, while still retaining MIS as the reinforcer. As in Study 4, the question of whether the 50”/, Success group would be more stable over trials than the 10 and 90’;,, groups was of special interest. The Type A personality is of medical interest because it represents a risk factor for coronary heart disease (e.g. Friedman and Rosenman, 1959; Roseman. Brand, Sholtz and Friedman, 1976). Although a summary of the characteristics of this personality type is beyond the scope of the present paper, it can be asserted that the evidence suggests that Type A individuals exhibit sympathetic nervous system hyperresponsivity in the cardiovascular system and that they are
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Appetitive
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behaviorally highly ‘active’. From the perspective of the motivational theory under discussion here, this combination of features suggests that a strong appetitive motivational system response might contribute to the etiology of Type A behavior. This reasoning led Perkins to examine the HR reaction of Type A vs Type B Ss in the response cost paradigm. The factors in this study were Incentive (54 vs O$), Personality (Type A vs Type B), % Success (10, 50, 90) and Trials (2-5bi.e. a 2 x 2 x 3 x 4 ANCOVA-with 10 Ss/cell. The MI groups received $6 at the beginning of Trial 2 and were told that each failure tone as a result of slow performance represented a loss of 54. The FO Ss were told that, in order to make the task more interesting, they began with 600 points and would lose 5 points for each failure tone. The results for Incentive and % Success are presented in Fig. 7 (collapsed across Personality and hence with 20 Ss/cell). The main effect of Incentive was significant (P < 0.01) and there was a trend toward an Incentive x % Success interaction (P < 0.10). The similarity of the results to Studies 4 and 5 suggests that employing a response cost paradigm did not alter the HR response. The absence of an interaction with Trials indicated again that the 50% Success group did not respond like Obrist’s ‘hard’-task group. The 50 and 90% groups resembled, within the limits of sampling fluctuation, those of Studies 4 and 5. The only large discrepancy was found in the problematic 10% Success/MI group, which showed a slightly greater HR increase than the FO groups in Perkins’ study, in contrast to a smaller response (actually, a decline) in Fisher’s study. With respect to the Type A factor (Fig. 8), there was a main effect of Personality (P < 0.001): Type A Ss showed a greater increase in HR to the feedback conditions (regardless of Incentives or % Success) than did Type Bs. A Personality x Incentive interaction (P < 0.05) reflected the greater efficacy of MI in producing differences between Type As and Type Bs. Although there was an interaction involving Personality x % Success x Trials (P < 0.05) it is probably uninterpretable. In summary, Type A Ss respond more strongly than Type Bs to the introduction of performance feedback, and this difference between Type As and Type Bs appears to be greater with MIS. Although these results require replication and extension to the simple reward paradigm, they are compatible with the intitial hypothesis that differences in an appetitive motivational system Putting this another way, insofar as the theory that contribute to the Type A/B distinction. appetitive motivational influences are largely responsible for psychological effects on HR is supported by the studies reported here, Perkins’ results offer a new perspective on Type A behavior.
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relative to Trial 1 as a function 54) and Personality (Type A vs in a response cost paradigm. from Perkins (1983).
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COMMENT
ON
THE
HR
STUDIES
These studies strongly support the hypothesis that appetitive motivation has an important effect on HR, apparently not attributable to cardiac-somatic coupling. The incentive effect on HR has been obtained in all of the seven studies considered here and, when examined, has shown a response proportional to the magnitude of incentive. It does not appear that aversive motivation associated with failure feedback or frustrative nonreward contributes to this effect, since the HR response is at least as large in the absence of evaluative feedback as when subjects receive some failure feedback (e.g. 90% success). Assuming that cardiac-somatic coupling and frustrative nonreward can be rejected as explanations for the incentive effect on HR, the appetitive hypothesis must be accepted and awarded full status as a psychological influence on HR. Perkins’ study has already demonstrated one application to the study of personality-the Type A behavior pattern. Whereas most studies in this area have focused on stress and aversive motivation with little theoretical development, his study was unusual in employing procedures developed for a specific theoretical appproach and in emphasizing appetitive motivation. The same approach might be fruitfully applied to other personality constructs which emphasize strong reward-seeking behavior+.g. impulsivity, some characteristics of extraversion and perhaps psychopathy. Where strong reward-seeking behavior is concerned, it is difficult at the behavioral level to choose between excessive appetitive motivation (sensitivity to rewards) and deficient inhibitory mechanisms (insensitivity to punishments and frustrative nonreward). It is hoped that evaluation of cardiac acceleration in response to rewards will indicate whether or not excessive appetitive motivation is present. More directly, there are two well-known theories of psychopathology which postulate a deficiency of hedonic motivation. One of the key symptoms of depression is ‘loss of interest’, and this symptom is particularly associated with autonomous or endogenous (Fowles and Gersh, 1979) or endogenomorphic (Klein, 1974) depression. This loss of interest has been attributed to loss of reinforcer effectiveness (e.g. Costello, 1972; Klein, 1974). If the cardiac response to incentives should distinguish between patients with a dysfunctional appetitive motivational system (i.e. who are unresponsive to all rewards) and those whose depression is more reactive to current environmental events (i.e. who do respond to rewards if present), it will be a valuable subtyping procedure. In a similar vein, clinical folklore has long employed the term anhedonia to describe some schizophrenics, especially socially-withdrawn schizophrenics (Depue, 1976). Whereas the loss of appetitive motivation in depression is more transient, the schizophrenic’s anhedonia is typically viewed as a trait, one undoubtedly contributing to the chronic poor adjustment seen in these patients. Although it seems likely that incentives other than money may be required for research with acutely-disturbed psychiatric patients, the present paradigm may be valuable for clinicallyrelated research with college students. For example, the development of an anhedonia scale for use with college students (Chapman, Chapman and Raulin, 1976) makes it possible to investigate the relationship between HR and anhedonia in college populations. REFERENCES Chapman L. J., Chapman J. P. and Raulin M. L. (1976) Scales for physical and social anhedonia. J. ahnorm. Psycho/. 85, 376382. Costello C. G. (1972) Depression: loss of reinforcer or loss of reinforcer effectiveness. Behav. Ther. 3, 24G247. Depue R. A. (1976) An activity-withdrawal distinction in schizophrenia: behavioral, clinical, brain damage, and neurophysiological correlates. J. abnorm. Psychol. 85, 174185. Elliott R. (I 969) Tonic heart rate: experiments on the effects of collative variables lead to a hypothesis about its motivational significance. J. Person. sot. Psycho/. 12, 21 l-228. Elliott R. (1974) The motivational significance of heart rate. In Cardiovascular Psychophysiology: Current Issues in Response Mechanisms, Biofeedback, and Methodology (Edited by Obrist P. A., Black A. H., Brener J. and DiCara L. V.). Aldine, Chicago, Ill. Fisher A. E. (1982) The effects of differing levels of incentive on human heart rate. Unpublished Master’s Thesis, University of Iowa, la. Fowles D. C. (1980) The three arousal model: implications of Gray’s two-factor learning theory for heart rate, electrodermal activity, and psychopathy. Psychophysiology 17, 87-104. Fowles D. C. (1982) Heart rate as an index of anxiety: failure of a hypothesis. In Focus on Cardiovascular Psychophysiology (Edited by Cacioppo J. T. and Petty R. E.). Guilford Press, New York.
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Fowles and Gersh F. (1979) Neurotic depression-I. The endogenous-neurotic distinction. In The Psychobiology of the Depressive Disorders: Implicationsfor the Effects of Stress (Edited by Depue R. A.). Academic Press, New York. Fowles D. C., Fisher A. E. and Tranel D. T. (1982) The heart beats to reward: the effect of monetary incentive on heart rate. Psychophysiology 19, 506-5 14. Friedman M. and Rosenman R. H. (1959) Association of specific overt behavior pattern with blood and cardiovascular finding. J. Am. med. Ass. 169, 12861296. Gray J. A. (1978) The neuropsychology of anxiety. Br. J. Psychol. 69, 417-434. Gray J. A. (1979) A neuropsychological theory of anxiety. In Emotions in Personality and Psychopathology (Edited by Izard C. E.). Plenum Press, New York. Klein D. F. (1974) Endogenomorphic depression: a conceptual and terminological revision. Archs gen. Psychiat. 31, 447454. Obrist P. A. (1976) The cardiovascular-behavioral interaction-As it appears today. Psychophysiology 13, 95-107. Perkins K. A. (1982) Heart rate change in Type A and Type B males as a function of incentive and level of task difficulty in a response cost paradigm. Unpublished Doctoral Dissertation, University of Iowa, Ia. Rosenman R. H., Brand R. J., Sholtz R. 1. and Friedman M. (1976) Multivariate prediction of coronary heart disease during 8.5-year follow-up in the W. Collaborative Group Study. Am. J. Cardiol. 37, 902-910. Tranel D. T. (1982) Human heart rate and electrodermal response as a function of monetarv incentive and frustrative nonreward. Unpublished Doctoral Dissertation, University of Iowa, Ia. Tranel D. T., Fisher A. E. and Fowles D. C. (1982) Magnitude of incentive effects on heart rate. Psychophysiology 19, 514-519.