Within-subject control designs and voluntary bidirectional control of cardiac rate: methodological comparison between pre-experiment and pretrial baselines

Control freaks: Towards optimal selection of control conditions for fMRI neurofeedback studies

fMRI Neurofeedback research employs many different control conditions. Currently, there is no consensus as to which control condition is best, and the answer depends on what aspects of the neurofeedback-training design one is trying to control for. These aspects can range from determining whether participants can learn to control brain activity via neurofeedback to determining whether there are clinically significant effects of the neurofeedback intervention. Lack of consensus over criteria for control conditions has hampered the design and interpretation of studies employing neurofeedback protocols. This paper presents an overview of the most commonly employed control conditions currently used in neurofeedback studies and discusses their advantages and disadvantages. Control conditions covered include no control, treatment-as-usual, bidirectional-regulation control, feedback of an alternative brain signal, sham feedback, and mental-rehearsal control. We conclude that the selection of the control condition(s) should be determined by the specific research goal of the study and best procedures that effectively control for relevant confounding factors.

Cardiac, respiratory and metabolic changes during static exercise and voluntary heart rate acceleration

Various ventilatory and metabolic parameters were monitored in 12 subjects while they performed each of three tasks: Voluntary cardiac acceleration with the aid of continuous heart rate feedback; a static hand-grip exercise at 1/3 maximum voluntary contraction; and a combined task involving both voluntary acceleration and exercise. Task order was counterbalanced across subjects and there were six 30 sec trials of each task. While reliable cardiac accelerations were recorded throughout, they were substantially greater with the combined task. This confirmed previous findings attesting that individuals can voluntarily elevate heart rate above levels induced by standard physical loads. However, the pattern of results for oxygen consumption and carbon dioxide production, with the most substantial increase in both also occurring for combined voluntary acceleration and exercise, suggested that the cardiac elevations superimposed on exercise levels were largely non-specific, i.e. they involved additional energy expenditure. Respiration volume increased during the performance of all three tasks, with the greatest increase again occurring in the combined tasks. The precise respiratory adjustments, in terms of rate and tidal volume, varied subtly among tasks; while all three tasks produced a rise in respiration rate, only the combined task increased tidal volume.

Voluntary heart rate lowering following a cardiovascular arousing task

The purpose of the research was to evaluate the effect of feedback-assisted voluntary control to lower heart rate (HR), following a non-somatic mediated task designed to induce cardiovascular activation. Twenty-seven male subjects participated in this study and were randomly divided into three groups. All subjects were submitted to an arousing mental arithmetic task for a 1 min period, followed either by a feedback-assisted HR lowering task (FG), by an unassisted HR lowering task (ICG), or by a relaxation period (RCG). During this period (2 min duration), ICG and RCG subjects were required, as a help for HR deceleration or relaxation, to track visually a sweeping line similar in form to the continuous analogue feedback of the FG subjects. This sequence, interspaced by a 1 min rest period, was repeated 10 times. Results showed that the mental arithmetic task was effective in producing consistent and repetitive HR acceleration. All three groups showed significative HR lowering during the following voluntary HR control or relaxation period. However, there was no difference in the speed or depth of HR lowering. It appeared that continuous-analogue feedback was not more effective than instructions to relax to assist HR return to lower levels.

Biofeedback and relaxation effects in electromyographic biofeedback training: a methodological note

The present study documented progressive reductions of electromyographic potentials in a biofeedback study involving instructions to 11 female and 5 male college students to both increase and decrease the feedback (and therefore the muscle tension). When only pre-experimental baselines were employed, electromyographic reductions were found with instructions to decrease the feedback. When repeated, nontreatment baseline conditions were employed as references for analysis, no electromyographic reductions were detected beyond the progressive reductions that occurred during those baselines.

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.

A re-examination of the relationship between locus of control and voluntary heart rate change

The present study was an attempt to resolve some of the inconsistencies and discrepancies in previous studies examining the relationship between Rotter's locus control construct and voluntary heart rate (HR) change. Twelve internals and 12 externals received two sessions (one week apart) of bidirectional HR control trials with or without feedback. Internals, relative to externals, were better able to increase their HR and showed more improved performance with feedback. Neither group was able to lower their HR significantly during any decrease phase of either session. It was suggested that (a) HR slowing may involve different psychophysiological processes than HR speeding, and/or (b) HR slowing may have been perceived to be a task involving chance rather than skill, in which case no difference between groups would be expected in light of the locus of control literature.