EMG stability as a biofeedback control

Factors that may confound comparisons between electromyographic (EMG) biofeedback training and its control conditions include feedback quality and experience of success. We investigated the usefulness of a control procedure designed to overcome these potential sources of confounding. The procedure consisted of training muscle tension stability. We used it as a control for frontal EMG relaxation training in children with asthma. To equate the groups for feedback quality and experience of success, we gave each child in the control condition audio feedback decreasing in pitch when muscle tension was at or near baseline levels, and feedback increasing in pitch when muscle tension was either substantially above or below baseline levels. Children in both groups were instructed to decrease the pitch of the tone. In comparison to children in the relaxation condition, the children in the control condition exhibited stable levels of muscle tension throughout eight training sessions. We concluded that feedback for stable muscle tension may be a useful control procedure for EMG biofeedback training whenever experimental and control procedures differ in either feedback quality of degree to which they permit subjects to experience success.This research was supported by NIH-Grant HL 27402. We are grateful to Paul Schnitter who constructed the EMG stability feedback device.     

EMG biofeedback and discriminative muscle control

The awareness model of biofeedback suggests that training teaches new skills or enhances performance at old skills, while the cognitive or feed-forward models suggest that biofeedback brings attention to the response of interest but does not actually increase task skill. In a test of the predictions made by these models, subjects were tested on one or more cross-modal matching tasks, provided brief training, and retested on the task(s). Thirty subjects participated in integer-matching tasks in which they were instructed to produce various levels of frontalis activity corresponding to the levels of a ratio scale. Forty-five subjects participated in a tone-matching task in which they tried to match their frontalis tension to the pitch of a tone. The results indicated that the groups receiving biofeedback training improved at the more difficult integer task and at the tone task. Subjects performed better on the integer tasks than at the tone task. Our findings suggest that an awareness model accounts for changes occurring during biofeedback training. However, an awareness model may be applicable only for tasks of moderate difficulty; for relatively easy tasks, a feed-forward model may be more appropriate. The clinical utility of cross-modal matching tasks is also described.     

EMG biofeedback and discriminative muscle control

The awareness model of biofeedback suggests that training teaches new skills or enhances performance at old skills, while the cognitive or feed-forward models suggest that biofeedback brings attention to the response of interest but does not actually increase task skill. In a test of the predictions made by these models, subjects were tested on one or more cross-modal matching tasks, provided brief training, and retested on the task(s). Thirty subjects participated in integer-matching tasks in which they were instructed to produce various levels of frontalis activity corresponding to the levels of a ratio scale. Forty-five subjects participated in a tone-matching task in which they tried to match their frontalis tension to the pitch of a tone. The results indicated that the groups receiving biofeedback training improved at the more difficult integer task and at the tone task. Subjects performed better on the integer tasks than at the tone task. Our findings suggest that an awareness model accounts for changes occurring during biofeedback training. However, an awareness model may be applicable only for tasks of moderate difficulty; for relatively easy tasks, a feed-forward model may be more appropriate. The clinical utility of cross-modal matching tasks is also described.This paper is based on a thesis conducted by the second author under the direction of the first author. Portions of this paper were presented at the annual meeting of the Association for Applied Psychophysiology and Biofeedback, March 1989, San Diego.     

Simultaneous biofeedback of heart rate and frontal EMG as a pretraining for the control of EEG theta activity

Following one base-line session, 20 normal subjects received four half hour sessions consisting of simultaneous feedback of heart rate and frontalis muscle (pretraining). Ten subjects received contingent (CF), the other ten noncontingent feedback (NCF). Subjects were asked to lower heart rate and frontal muscle tension (EMG). Heart rate within sessions decreased up to 19 bpm, with a mean of 4 bpm for the CF group. There was only a weak decrease over sessions, however, because of the strong habituation effect. The following events accompanied the heart rate decrease: (1) an increase of the variability of the heart rate, (2) a decrease of the variance of the EMG, (3) an increased correlation between heart rate slowing and EMG decrease, and (4) an increasing subjective experience of control of heart rate and EMG. After pretraining, subjects received eight sessions of auditory feedback of their frontal EEG theta activity (four sessions with CF and four sessions with NCF in balanced order). There was a weak increase of theta for the CF condition over sessions, but a decrease within the sessions. Pretraining on heart rate and frontal EMG control had no influence on the performance during theta training. It was hypothesized that control of heart rate slowing and theta control involve different mechanisms.     

Generalization of EMG biofeedback training

Five young adults received audio biofeedback training to reduce trapezius EMG levels while they engaged in reading in an office, seated at a table. A multiple-baseline-across subjects design was employed in two separate studies. After training, all subjects demonstrated reduced EMG levels while reading in a home or library setting. The first study suggested that subjects reduced EMG levels by minimizing movements and altering their postures; the second study systematically demonstrated changes in such behavior, which was correlated with EMG levels. The data provide evidence that EMG biofeedback resulted in response generalization across several motoric classes, and in stimulus generalization from the training setting to the natural environment. The importance of assessing generalization is discussed.     

Generalization of EMG biofeedback training

Five young adults received audio biofeedback training to reduce trapezius EMG levels while they engaged in reading in an office, seated at a table. A multiple-baseline-across subjects design was employed in two separate studies. After training, all subjects demonstrated reduced EMG levels while reading in a home or library setting. The first study suggested that subjects reduced EMG levels by minimizing movements and altering their postures; the second study systematically demonstrated changes in such behavior, which was correlated with EMG levels. The data provide evidence that EMG biofeedback resulted in response generalization across several motoric classes, and in stimulus generalization from the training setting to the natural environment. The importance of assessing generalization is discussed.     

The role of EMG awareness in EMG biofeedback learning

Underlying most research on biofeedback learning is a theoretical model of the processes involved. The current study tested a prediction from the Awareness Model: High initial EMG awareness should facilitate response control during EMG biofeedback training. Seventy-two undergraduates were assessed for forehead EMG awareness by asking them to produce target responses from 1.0 to 5.0 µV every 15 s for 16 trials. Based on this assessment, two groups (high and low awareness) were trained for 64 trials to produce these target levels with either EMG biofeedback, practice (no feedback), or noncontingent EMG feedback. A transfer task was identical to the initial assessment. During training, the biofeedback group deviated less from target than the practice and noncontingent groups. The biofeedback group was the only group to improve from initial EMG awareness activity. During transfer, only the low awareness biofeedback group remained below initial EMG awareness level. These findings can be interpreted in terms of the Two-Process Model.     

EMG biofeedback treatment of torticollis: a controlled outcome study.

Successful treatment of torticollis with electromyographic (EMG) biofeedback has been reported in a number of single case and single group studies. The present investigation represents the first controlled outcome study. Twelve torticollis patients were randomly assigned to EMG biofeedback or relaxation training and graded neck exercises (RGP). The procedure involved three sessions of baseline assessment, 15 sessions of EMG BF or RGP, 6 sessions of EMG BF or RGP plus home-management, 6 sessions of home-management alone, and follow-up 3 months after the end of treatment. A variety of outcome measures were used including physiological (EMG from the two sternocleidomastoid muscles, skin conductance level), behavioral (angle of head deviation, range of movement of the head), and self-report (depression, functional disability, body concept), therapist and "significant other" reports and independent observer assessment of videos. In both groups, neck muscle activity was reduced from pre- to posttreatment. This reduction was greater in the EMG biofeedback group. There was evidence of feedback-specific neck muscle relaxation in the EMG biofeedback group. Therefore, the outcome was not due to nonspecific factors and could be attributed to feedback-specific effects. Changes in skin conductance level showed that neck muscle relaxation was not simply mediated by a general reduction of "arousal." Significant improvements of extent of head deviation, and range of movement of the head, as well as reductions of depression were present, which were not different in the two groups. At the end of treatment, no patient was asymptomatic. Any therapeutic benefit was generally maintained at follow-up. The results and the procedural simplicity of RGP make the issue of cost-efficacy of EMG biofeedback a pertinent one. Further controlled outcome studies of EMG biofeedback treatment of torticollis with larger samples are required.     

Cognitive self-control factors in EMG biofeedback

This study investigated the efficacy of manipulation of cognitive self-control expectancy in EMG biofeedback training. It was predicted that a treatment procedure, which includes a positive-cognitive stage that establishes and reinforces a positive self-control belief system and also includes a training stage in EMG biofeedback, will be more effective in achieving a reduction in EMG activity than a treatment procedure which includes a negative-cognitive stage and which also includes ambiguous features prior to training and a treatment approach solely concerned with training. The study consisted of four groups with 10 subjects in each. In one group, expectation for inner control ability was created prior to actual training in reducing EMG activity. In the second group, expectation for negative self-control ability was created prior to EMG training. The third group only underwent the actual training in EMG. The fourth group served as a control group. The results show that the positive-cognitive self-control group was significantly more effective in reducing muscle activity than the other groups.     

Effects of an EMG biofeedback relaxation program on the control of diabetes

It was hypothesized that EMG biofeedback relaxation training, applied to a diabetic patient, would result in a decreased level of insulin with fewer episodes of ketoacidosis. A 20-year-old female, diabetic since age nine, kept daily records of insulin doses and rated herself on an emotionality and a diabetic scale. A full-semester baseline was taken. This was followed by a semester-long training program during which the patient practiced relaxing her frontalis muscle with a portable EMG feedback unit which produced a geiger-counter-like click feedback. A cassette-tape series was used along with the portable EMG. The patient was encouraged to practice twice each day and to attempt to maintain a relaxed state even when not in the practice situation. The daily use of the portable unit was terminated at the end of the semester. In addition, the patient ceased practicing twice daily with the cassette tape. Daily insulin averaged 85 units for the six-week baseline and 59 for the final six weeks of the training period. Moreover, at the end of the training period the average dose had reached 43 units. During the training period the patient rated herself as decreasing in emotionality and in diabetic fluctuations.Supported by the National Institute of Mental Health Grant MH-15596.     

A comparison of frontal EMG biofeedback and neck EMG biofeedback in the treatment of muscle-contraction headache

EMG biofeedback from the frontal area (FFB) was compared to EMG biofeedback from the neck (NFB) in the treatment of chronic muscle-contraction headache. Both treatment groups (N=10) evidenced significant decreases in reported headache activity, with the NFB group also significantly reducing medication consumption. An analysis of EMG changes suggested that subjects were able to produce large within-session changes in EMG activity during initial sessions, with the major effect of additional training being an increase in speed with which these changes occurred. In neither group, however, did changes in EMG activity correspond closely to changes in reported headache activity.     

Effects of EMG biofeedback on diabetes

A case is described in which a juvenile-onset insulin-requiring diabetic was given frontalis EMG biofeedback. For 6 years prior to biofeedback training, the subject had been healthy and stable on 22–24 units regular insulin injected once daily. During 8 weeks of standard feedback training for relaxation of frontalis muscle activity, the subject twice reduced her daily insulin dosages. At the end of 8 weeks, the subject was receiving 17–18 units regular insulin daily but was still unstable, sometimes being hyperglycemic, sometimes hypoglycemic. Because of disturbing symptoms associated with this instability, biofeedback was discontinued for 6 months, at which time the subject was again healthy and stable on the equivalent of 18–19 units regular insulin daily. After this period, biofeedback was again given for 1 week, but the subject again became highly unstable and biofeedback was permanently stopped. Caution is suggested when dealing with diabetic patients.     

Ocular and stabilization feedback: an evaluation of two EMG biofeedback control procedures

This study evaluated the adequacy of two novel EMG biofeedback control procedures. During a single training session, 36 subjects received either contingent EMG feedback from the frontal region (Veridical), contingent feedback for vertical eye movements (Ocular), or a feedback condition where the signal increased with deviations in any direction from baseline EMG levels (Stabilization). The results supported the use of Ocular but not Stabilization feedback as a control procedure in frontalis EMG biofeedback studies. Ocular feedback did not produce reductions in frontalis EMG but did lead to changes in subjective measures of nonspecific treatment effects that were at least comparable to those obtained with Veridical feedback. Stabilization subjects produced small but significant reductions in EMG, felt the most bored as a result of their feedback training, and were the most likely to rate themselves as having received false feedback. The implications of attribution theory and multiprocess relaxation theory for the evaluation of nonspecific treatment effects are discussed.     

Yawning: a possible confounding variable in EMG biofeedback studies

An elderly hemiplegic patient participating in an EMG biofeedback training program was observed to produce a synergistic flexion movement of the plegic (determined by functional evaluations) upper limb while yawning. In the course of the training sessions the electrical activity of the anterior deltoid (the target muscle) was recorded during yawning. These peak EMG values were greatly facilitated in comparison with the session mean peak values obtained during an attempted maximum voluntary isometric contraction (shoulder flexion) of the same limb (e.g., Trial 1: 85.00 vs. 4.33 microV). The possibility of yawning as a confounding variable in EMG biofeedback studies is presented and discussed.     

Specific and nonspecific effects of EMG biofeedback

This study investigated the effects of performance feedback and EMG biofeedback on perceptions of the self (i.e., self-esteem, self-control, self-efficacy, and locus of control) as well as on a self-control behavior (study skills) the subjects performed outside the laboratory. Forty-seven college students were randomly assigned to one of four groups in a 2(high and low success feedback) × 2(true and false EMG biofeedback) factorial experiment with repeated measures. All of the participants received four sessions of EMG biofeedback, and later they were asked to self-monitor their study habits for 2 weeks. Results showed that the self-esteem measure and perceptions of study skills improvement were differentially affected by success feedback but unrelated to the true or false EMG manipulation. Shifts toward an internal locus of control and perceptions of improved self-control were also noted, but they were independent of the subjects' group membership. Implication of the results are briefly discussed.     

Detection of noncontingent feedback in EMG biofeedback

Noncontingent feedback is frequently used as a placebo control procedure in biofeedback research. Researchers, however, have criticized this procedure for lacking credibility because of easy detection. The present study examined detection of false feedback in biofeedback with EMG. Contingent feedback (CF), truly random false feedback (FF), and controlled false feedback (CFF) groups were compared for changes in EMG levels, report of inaccurate feedback, and report of learning muscle activity reduction. The results indicated that FF procedures are easily detected; therefore, difference found between the FF and CF groups may be influenced by extraneous variables. The CFF group did not detect false feedback, but subjects reported some suspicions in later trials. With more trials, CFF may have also been detected. These results indicate a need for more attention to appropriate placebo control procedures in evaluating the parameters and efficacy of biofeedback.     

Parasympathetic rebound following EMG biofeedback training: a case study

The self-regulation literature contains very few reports of negative side-effects stemming from biofeedback training. Nevertheless, the case reported here is unique in that immediately following each of several early EMG feedback sessions, an otherwise headache-free patient reported an acute attack of headache and nausea. These attacks, the conditions under which they appeared, and the conditions leading to their remission will be described. Discussion will focus on the possible physiological mechanisms involved.     

Detection of noncontingent feedback in EMG biofeedback

Noncontingent feedback is frequently used as a placebo control procedure in biofeedback research. Researchers, however, have criticized this procedure for lacking credibility because of easy detection. The present study examined detection of false feedback in biofeedback with EMG. Contingent feedback (CF), truly random false feedback (FF), and controlled false feedback (CFF) groups were compared for changes in EMG levels, report of inaccurate feedback, and report of learning muscle activity reduction. The results indicated that FF procedures are easily detected; therefore, differences found between the FF and CF groups may be influenced by extraneous variables. The CFF group did not detect false feedback, but subjects reported some suspicions in later trials. With more trials, CFF may have also been detected. These results indicate a need for more attention to appropriate placebo control procedures in evaluating the parameters and efficacy of biofeedback.