Interoceptive discrimination in intact humans: detection of cardiac activity

The effects of physical fitness and exercise on cardiac awareness

This experiment was run to further evaluate the role of individual difference factors in perception of heart beats (cardiac awareness). The present study examined 24 male subjects who showed high and moderate levels of physical fitness. Cardiac awareness was examined using Brener-Jones type discrimination trials. Subjects discriminated first while standing quietly on a treadmill (32 trials), then while walking briskly on a motorized treadmill (32 trials), and finally during recovery from exercise (elevated HR but behavioral quiescence) (16 trials). Results showed that only the moderate fitness group showed heightened awareness during exercise, while both groups showed greater than chance awareness during recovery from exercise. Neither group was highly aware while resting before exercise. These results fail to support notions that high fitness distance runners are highly aware of cardiac function during exercise. A number of reasons for this finding are discussed.

Discrimination of blood glucose levels in insulin-dependent diabetics

Three insulin-dependent diabetic adults were exposed to a blood glucose discrimination training program. Following baseline, during which subjects estimated their blood glucose levels twice daily, subjects received immediate feedback regarding the accuracy of their estimation. The procedure resulted in a large increase in accuracy of blood glucose level estimation. The implications of the findings are discussed.

Concurrent assessment of heart rate discrimination and control

A procedure was devised to investigate discrimination and control of heart rate (HR) concurrently. Eighteen volunteers were divided into two equal groups instructed either to increase or to decrease HR during four experimental sessions. In addition, subjects were required to indicate whenever they thought they were successful during the HR control task by pressing a switch. Activation of the switch automatically enabled the presentation of a feedback tone provided that the HR level at that moment, met a preset criterion of change. The feedback was not available during pre- and post-training testing periods. Responses to bidirectional HR control instructions alone were also investigated. Respiration volume and general movement were recorded throughout. While the group given HR increase instructions improved both their discrimination and control performances, the group instructed to decrease HR did not improve. It is suggested that the optimal procedures for training HR increases and decreases may differ, but that the relationship between discrimination and control posited by the calibration model can accommodate these differences.

An experimental analysis of discrimination of pulse transit time

The present study attempted to determine if individuals could be trained to discriminate changes in their own pulse transit time, an indirect estimate of relative (systolic) blood pressure. A single-subject ABAB reversal-reinstatement design was used in an experimental analysis of the effects of feedback on pulse transit time discrimination in a normotensive and essential hypertensive subject. Subjects engaged a response button on a free-operant schedule each time they felt pulse transit time was momentarily below a predetermined mean. After baseline, visual feedback was provided contingent on correct responses (feedback) and incorrect responses (reversal). Procedures also assessed the role of respiration as a possible discriminative stimulus. For both subjects discrimination improved during feedback, showed disruption when the reversal was implemented, and subsequently improved during the second feedback phase. Respiration did not appear to have served as the discriminative stimulus. Results are discussed in terms of the need for refining procedures, especially to ensure generalization to no-feedback conditions, and the potential applications and importance of training of pulse transit time.

Voluntary heart rate control: the role of individual differences

It is a frequent observation that individuals differ markedly in their success at voluntary heart rate control. Several dispositional variables have now received attention as possible sources of such individual variation. These are critically reviewed under the following headings: resting and stimulus-elicited heart rate characteristics; autonomic and cardiac perception; imagery vividness; locus of control; trait anxiety. It is concluded that the research on individual differences in cardiac control to date is contributing to a clearer understanding of the mechanisms underlying control. However, for this contribution to be sustained, research needs to service explicit hypotheses about mediating processes. The often arbitrary and atheoretical practices that characterize much of the research in the more general context of individual differences in physiological activity must be avoided.

Effect of heart-rate control training on heart-rate discrimination

4 subjects were exposed to discrimination-testing procedures before and later biofeedback training to increase and decrease their heart rates. Results indicated significant increases and decreases in heart rate, as well as a significant improvement in accuracy of discrimination. The results suggest improvements in discrimination may occur as a function of feedback training.

Cardiac perception and cardiac control. A review

The evidence regarding specific cardiac perception and discrimination, and its relationship to voluntary cardiac control, is critically reviewed. Studies are considered in three sections, depending on the method used to assess cardiac perception: questionnaire assessment, discrimination procedures, and heartbeat tracking. The heartbeat tracking procedure would appear to suffer least from interpretative difficulties. Recommendations are made regarding the style of analysis used to assess heartbeat perception in such tracking tasks.

Effects of biofeedback on the discrimination of electrodermal activity

Twenty-four subjects were tested on their ability to discriminate between the presence and absence of negative skin potential responses before and after training to control skin potential. Training consisted of 52 discrete 30-second trials during which subjects were asked either to increase or to inhibit palmar sweating. Subjects in groups N and P were provided with analogue feedback on their skin potential activity. Group N was correctly informed that increases in sweating were indicated by increases in the negativity of skin potential; group P was misinformed that these were indicated by increases in the positivity of skin potential. Subjects in the control (C) group received no feedback. Reliable evidence of discrimination was obtained only in groups N and P, following training. However, reliable evidence of control was obtained only in group N. Thus, training to control skin potential led to an ability to identify afferentation associated with the more common (i.e., negative) skin potential responses, even though biofeedback training appeared unsuccessful in the case of group P. These findings are discussed in the context of "discrimination" or "awareness" accounts of the process of acquiring control of internal response.

Biofeedback, self-control, and self-management

A common goal of biofeedback is self-control of physiologic responses. The conceptions and paradigms of the literature on self-control of motoric and cognitive responses were surveyed to provide a basis for the self-control of physiologic responses. An operational definition of self-control was advanced, and self-control was placed in the framework of a general self-management strategy which included discrimination and maintenance components.