Feedback Effects and Respiratory Involvement in Voluntary Control of Heart Rate

One within-subject single session experiment involving 30 subjects and one between-subject single session experiment involving 42 subjects were performed to evaluate the effects of augmented sensory feedback and to specify the nature of cardiac-respiratory relationships during attempted bi-directional control of heart rate (HR). Subjects were instructed to attempt to control HR while maintaining a constant respiration rate (RR), and were provided with either no feedback, HR feedback, or HR and RR feedback of the “digital” proportional type. In addition to measures of heart and respiratory period, a measure of respiratory volume was included in the second experiment. Results of both experiments indicate that (1) subjects can significantly increase and decrease HR; (2) feedback does not affect the magnitude or consistency of HR control; (3) significant parallel changes in RR accompany changes in HR regardless of the amount of feedback provided; (4) significant increases in respiratory volume accompany HR increases; and (5) large magnitude HR changes arc produced by some subjects within the single session. Implications of these findings for the concomitance model of autonomic and central nervous system interactions; for single vs multiple training sessions; for the use of paced respiration; and for a learning model of HR control are discussed.     

The Interaction of Instruction Components with Cybernetic Feedback Effects in the Voluntary Control of Human Heart Rate

Two groups of 20 subjects were presented with either contingent or yoked feedback for heart rate increase and decrease. Subjects were instructed to either attend to their heart (attention instructions) or to increase or decrease their physiological activity (direction instructions). Half of each contingent group made the signal go on for HR increase (tone-on feedback) and off for decrease. The other half made the signal go off for increase (tone-off feedback) and on for decrease. It was found that direction instructions led to significantly better HR control than attention instructions for yoked but not for true feedback. For true feedback, tone-on led to HR increase, while tone-off interfered, leading to overall HR decrease. This did not occur for yoked feedback, suggesting the importance of contingent feedback in this effect. An additional finding of this study was that subjects' self-ratings of control were identical for true and yoked subjects, and did not correspond to their actual degree of control, suggesting that the feedback effects were mediated unconsciously. It was concluded that the direction component of HR instructions may obscure true cybernetic feedback effects which emerge through the manipulation of contingency and positive/negative feedback loops.     

The Role of Feedback in Control of Heart Rate Variability

The effects of contingent feedback (CF), non-contingent feedback (NCF). and no feedback (NF) on heart rate (HR) variability control were studied. Nine matched trios of subjects were given (ruining in HR variability control on 3 consecutive days. CF and NCF subjects attempted HR, variability control while HR feedback was continuously presented, and NF subjects attempted HR variability control without feedback. During the training periods the CF group produced reliably-lower mean HR variance than the NF group, but the NCF group was not reliably different from either of those groups. There was no significant difference among groups in negative linear trend across training periods, and the CF group did not continue to produce decreasing HR variances over sessions. However, the CF and NCF groups showed reliable quadratic trends, indicating an initial drop in HR variance followed by a return to pretraining levels. Both CF and NCF groups showed rapid, reliable increases in respiration rate during training periods. The results pose serious problems for studies which have reported feedback-related control of HR variability.     

Large Magnitude Voluntary Heart Rate Changes

An experiment was performed to demonstrate methods for enabling subjects (Ss) to produce large magnitude heart rate (HR) changes under conditions which include adequate controls for basal HR changes and elicitation of the HR response by breathing changes. The methods used were an attempt to optimize motivational, feedback, and practice variables. Of 9 Ss, 6 displayed mean HR increases ranging from 16.7 bpm to 35.2 bpm. The greatest mean HR decrease for any S was 3.1 bpm. Control procedures indicated that breathing changes accompanying large increases in HR were not sufficient to account for the magnitude of HR change.     

Learning to Control Heart Rate: Binary vs Analogue Feedback

Twenty-two male volunteers participated in an experiment designed to test the efficiency of two procedures, one emphasizing analogue and the other binary feedback, in training human subjects (Ss) to change their heart rate. Ss were seen for 7 separate sessions, which included 2 training sessions in speeding heart rate and 2 devoted to slowing. Both heart rate and respiration cycle length were recorded. The timing of the experiment, presentation of instructions, feedback, data acquisition, and primary data reduction were all accomplished in real-time by a computer. The feedback mediated acquisition of directional changes in heart rate was demonstrated, and these changes were sustained on instruction with feedback removed. No differences between the binary and analogue procedures were noted for slowing. However, the analogue display prompted significantly greater instructed acceleration than the binary method. An important distinction was made between organ feedback (heart activity) and task performance feedback (relative success or failure). It was noted that the acquisition of heart rate speeding and slowing appear to involve different psychophysiological mechanisms.     

Effects of Binary and Proportional Feedback on Bidirectional Control of Heart Rate

Six male and 6 female volunteers formed three groups of 4 subjects in a study on the efficacy of different forms of visual feedback on control of heart rate (HR). One group received proportional feedback from a meter plus a binary success signal, one group received only proportional feedback, and one group received only the binary signal. Subjects received 6 acquisition sessions and 4 extinction sessions. For HR increase, groups receiving proportional feedback showed mean control over the last 2 acquisition sessions of +10 bpm, whereas the group receiving only binary feedback showed control of +4 bpm. For HR decrease, both groups receiving proportional feedback showed mean control over the last 2 acquisition sessions of -4 bpm, whereas the group receiving only binary feedback showed negligible control. During extinction there was no immediate reduction hi control of either HR increase or HR decrease but both declined over extinction sessions. Results indicate that proportional feedback is clearly superior to binary feedback, and that the addition of a binary signal to proportional feedback does not reliably enhance control. Results are consistent with an operant conditioning interpretation of feedback control.     

Large Magnitude Heart Rate Changes in Subjects Instructed to Change Their Heart Rates and Given Exteroceptive Feedback

Four subjects who were given exteroceptive, auditory and visual feedback, and were asked to raise and to lower their heart rate on signal, were able to produce large magnitude changes in both directions. The fact that some of these changes occurred immediately suggests that feedback may not be as important as some authors have suggested. Respiratory changes and changes in muscle tension did not appear to be mediators.     

The Relationship of Locus of Control, Self-Report Measures, and Feedback to the Voluntary Control of Heart Rate

Forty internal and external locus of control subjects (Ss) were instructed to control their heart rate on 8 trial pairs. Each trial pair consisted of an increase and a decrease heart rate condition with the order being counterbalanced across Ss. On the last 4 heart rate control trials, the Ss were given visual feedback concerning the time interval between each heart beat via a light panel of 16 check lights. The major findings of this study were: (1) feedback significantly increased the magnitude of the IBI changes across all Ss; (2) locus of control differences were found across all trials with the internal locus of control Ss being able to increase their heart rate better than the external locus of control Ss, and the external locus of control Ss were better able to decrease heart rate as compared with the internals; and (3) self-report measures demonstrated that external and internal locus of control Ss adopted different strategies for controlling heart rate, and these strategies were related to previous psychophysiological research not requiring the direct control of heart rate.     

Voluntary Heart Rate Control During Static Muscular Effort

To test the hypothesis that voluntary heart rate (HR) control is possible with simultaneous muscular effort, 8 male subjects were trained in feedback assisted bidirectional HR control, and also practiced hand grip exercises requiring different levels of effort for 3 consecutive daily sessions. In a fourth session subjects were required to increase and decrease HR while simultaneously performing muscle contractions of 0%, 10%, 30% and 50% of maximum voluntary contractions. Substantial and reliable variations in HR were produced by instructions and by muscular effort during the first 3 sessions; and in the fourth session bidirectional HR control continued even with the relatively elevated baselines induced by muscular effort. Concomitant chin EMG levels did not vary with degree of muscular effort nor with instructions to increase or decrease HR, but increased over the course of any type of trial. Discussion suggests the use of artificially elevated baselines as a strategy for studying HR deceleration and concludes that the present study provides strong evidence of subjects' abilities to voluntarily control HR during muscular effort. This conclusion lends support to the notion that biofeedback therapies may be of clinical utility in real life by modulating the eliciting effects of stressors.     

Psychological and Physiological Variables Associated With Large Magnitude Voluntary Heart Rate Changes

Forty subjects, given binary and proportional auditory and visual feedback and asked to raise and lower their heart rate on signal, were able to produce increases of up to 46 bpm and decreases of up to 14 bpm, with a mean increase over 5 experimental days of 11 bpm and a decrease of 5 bpm. Increases in both diastolic and systolic blood pressure and increases in skin potential level and number of skin potential responses accompanied voluntary increases in heart rate but not decreases. Subjects with the highest resting heart rate variability and skin potential level were best able to raise their heart rate. Subjects with the highest resting heart rate and highest resting heart rate variability were best able to decrease the heart rate. Subjects with high Ego Strength scores (or low Welsh's Factor A scores) on the MMPI were best able to control their heart rate. The Ego Strength score, resting heart rate, and resting heart rate variability were all significantly intercorrelated. Subjects showed marked individual differences in ability to control heart rate, although there was a significant correlation between ability to raise and ability to lower heart rate.     

The Effects of Immediate Feedback Upon Voluntary Control of Salivary Rate

Thirteen human subjects (Ss) were given immediate auditory feedback concerning their salivary rates and were asked both to increase and to decrease their rates during a series of 30-sec trials. Significant decreases, but not increases, in salivary rate were obtained relative to baseline. During the second half of the experiment, when feedback was omitted until the end of each trial, Ss maintained significant differential response rates between increase and decrease trials, but the reliability of decreases from expected baseline was reduced. Thirteen control Ss, who received feedback only at the end of each trial during both halves of the experiment, were unable to alter their rates during either half. Salivation on increase and decrease trials was not systematically correlated with changes in either heart rate or breathing rate in the immediate feedback group.     

Voluntary Heart Rate Control as a Function of Individual Differences in Electrodermal Lability

Twenty-four male subjects were run in a paradigm in which they were first asked to rest for 10 min and then given 20 1-min training trials of analog and digital feedback of their heart rate, with instructions to increase the rate. Subjects were rewarded with 0.2 cents for each interbeat interval that was faster than a designated criterion. Subjects were subdivided into “labile” and “stabile” groups on the basis of frequency of spontaneous skin conductance fluctuations during the baseline period. Mean heart rate for the training trials was compared with the baseline period for the most labile and most stabile subjects. Results indicated that there was a significant treatment effect for stabile subjects only, but not for labile subjects.     

Voluntary Control and Reactivity of Human Heart Rate

Factors in human voluntary heart rate control with and without external feedback were studied. Average voluntary heart rate control in the laboratory was comparable to the range of heart rates obtained during accelerative-decelerative ‘reactivity’ tasks in the laboratory and to heart rates obtained during various situation* outside of the laboratory. However, cardiac rate reactivity did not reliably predict voluntary control performance across subjects (Ss). With full instructions, Ss were able to increase but not decrease heart rate relative to resting levels before feedback was provided. With full-scale meter feedback. Ss could both increase and decrease heart rate relative to resting levels. Performance in Bidirectional control during feedback remained constant. The ability both to increase and to decrease heart rate transferred to the postfeedback. no-meter condition. Reversing the meaning of the Up and Down cue lights during post-feedback for half of the As had no deleterious effect on bidirectional heart rate control. The importance of physiological and situational constraints in Bidirectional heart rate control is discussed.     

Effect of Feedback Sensitivity Upon Learned Heart Rate Acceleration

Twelve undergraduate volunteers received 12 sessions of heart rate biofeedback training involving one of two experimental conditions. One-half of the subjects received 4 sessions of high sensitivity analogue heart rate biofeedback, followed by 4 sessions of low sensitivity feedback, and then, 4 final sessions of high sensitivity feedback. The other half of the subjects received the exact opposite order of feedback conditions. All subjects were instructed to accelerate heart rate during 8 trials in each session. The results were contrary to the hypothesis derived from a motor skills model of visceral learning, i.e., the low feedback sensitivity condition consistently produced larger magnitude heart rate acceleration in comparison to the high sensitivity condition. These findings were discussed in terms of methodological suggestions for future research and in terms of the motor skills model of visceral learning.     

Heart rate control under conditions of augmented sensory feedback

Five human Ss were presented with a high frequency tone on the emission of each short inter-heartbeat interval and a low frequency tone on the emission of each long inter-heartbeat interval. Under these conditions, all Ss learned within a short period of time to produce significantly lower heart rates in the presence of one visual stimulus than in the presence of another. On the basis of this finding, it is suggested that an important determinant of where a given response falls on the voluntary/involuntary continuum is the availability of specific feedback from the response in question.     

Heart Rate Perception and Heart Rate Control

Twenty-one subjects look the Autonomic Perception Questionnaire (APQ) and later were given another test of ability to perceive heart activity. The second test involved subjects' tracking of their own heart rates (HR). They were then tested for ability to increase and decrease HR from their resting baseline levels. No significant relationships were found between HR control and APQ score. HR decrease success seemed to depend mainly on respiration differences between rest and decrease periods. The subjects who achieved high scores on the heart tracking test increased HR significantly better than did low scorers. This heart perception vs HR increase relationship did not depend upon respiration rate, respiration amplitude, or baseline HR differences between high and low scorers on the tracking test. A low correlation between APQ and tracking score seemed to indicate that the two perception tests measured different attributes of the subjects.     

Heart Rate as a Discriminative Stimulus

Two experiments were performed to evaluate characteristics of heart activity as discriminative stimuli. In Study I two multiple baseline across subjects designs were utilized to assess the efficacy of trial and error and fading procedures in increasing the detection of heart rate activity above and below an average level. Both trial and error and fading procedures were effective in increasing discrimination accuracy. A 4.4 bpm interval around the subject's mean heart rate was employed as the discriminative stimulus in Study II. Significant stimulus control exerted by the criterion stimuli was found during both training and testing conditions. Experimental procedures were discussed for determining which sensory events in a complex stimulus dimension such as a physiological change are actually exerting stimulus control.     

Sources of Information Which Affect Training and Raising of Heart Rate

This study was concerned with the effects of cardiac information and reinforcement on raising heart rate (HR). The experiment consisted of a 3 × 2 design with three types of cardiac information and two reinforcement conditions. The cardiac information given to Ss consisted of instructions to control an internal response (no specific HR information), instructions to increase HR (specific HR information), or instructions to increase HR while hearing heart beats through earphones (augmented HR information). External reinforcement was given to one-half of these Ss, while the remaining Ss received no external reinforcement. Sixty female undergraduates were randomly assigned to one of these six experimental groups. Analyses of these data indicate that Ss in both the augmented and specific HR information groups were able to increase their HR. The no specific HR information groups showed no increases in HR, suggesting that awareness of the criterion response plays an important role in raising HR. No differences were found between the reinforcement conditions.     

Effects of Instructions and Contingency of Reinforcement on the Operant Conditioning of Human Phasic Heart Rate Change

The aim of these studies was to determine the effects of instructions and reinforcement contingency on phasic heart rate (HR) change. In Exp. I, 36 human subjects were given 20 conditioning trials with a muscletensing task which produced a phasic HR acceleration. The experimental manipulation produced an elevated baseline and allowed for the observation of instructed HR change during exercise. A 2 × 2 between subject design varied instructions (to increase or decrease the phasic tension-induced HR acceleration) and contingency (whether the verbal reinforcement was contingent on or unrelated to HR change) as factors. There was a significant instructional effect at the end of conditioning, with increase subjects producing more HR acceleration and decrease subjects less acceleration relative to pretrials. The instructional effect developed over trials and decrease subjects significantly improved with practice. There was no difference between contingent and non-contingent groups in either of the two conditions in ability to change HR in the instructed direction. This study shows the usefulness of the elevated baseline technique for cardiac research. A second experiment demonstrated that, in subjects not instructed to attempt HR change, the phasic HR response did not change in magnitude over conditioning. The results of these studies indicate that subjects are able to control phasic HR during physical-stress induced tension but biofeedback is not relevant for the production of such HR changes.     

Utility of Voluntary Control of Respiration and Biofeedback for Increasing and Decreasing Heart Rate

Ninety-six subjects participated in an experiment conducted to determine the separate and combined effects of respiratory control and biofeedback on control of heart rate (HR). The results indicated, first, that controlling respiration enabled subjects to reliably (p < .001) increase HR but did not enable them to decrease HR, and second, that HR biofeedback did not enable subjects to change their HR more than they did when simply instructed to do so and not given biofeedback. These results are consistent with and add to previous findings concerning respiratory control, biofeedback and HR.