The effects of vibrotactile masking on heartbeat detection: Evidence that somatosensory mechanoreceptors transduce heartbeat sensations.

The ability to detect heartbeat sensations is the most common basis for inferring individual differences in sensitivity to the interoceptive stimuli generated by the visceral activity. While the sensory sources of heartbeat sensations have yet to be identified, there is a growing consensus that visceral sensation, in general, is supported not only by the interoceptive system but also by the somatosensory system, and even by exteroception. The current experiment sought evidence on this issue by exploring the effects of masking the functions of somatosensory Pacinian and non-Pacinian mechanoreceptors on the ability to detect heartbeat sensations. Twelve verified heartbeat detectors completed a multi-session experiment in which they judged heartbeat-tone and light-tone simultaneity under two vibrotactile masking conditions involving the stimulation of the sternum: (a) using 250 Hz vibrotactile stimuli to mask the Pacinian channel, and (b) using 6 Hz vibrotactile stimuli to mask the non-Pacinian channel. A no-vibration control condition in which no masking stimuli were presented was also implemented. Presentation of both the 250 Hz and the 6 Hz masking stimuli impaired the ability to judge the simultaneity of heartbeats and tones but did not influence the ability to judge the simultaneity of stimuli presented to different exteroceptive modalities (lights and tones). Our findings reinforce the view that the somatosensory system is involved in cardioception and support the conclusion that both Pacinian and non-Pacinian somatosensory mechanoreceptors are implicated in heartbeat detection.

Heartbeat counting is unrelated to heartbeat detection: A comparison of methods to quantify interoception.

Recent research has identified individual differences in interoceptive sensitivity as a key source of variation in action, cognition, and emotion. This research has relied heavily on a single method for assessing interoceptive sensitivity: the accuracy of counting heartbeats while at rest. The validity of this method was assessed here by comparing the heartbeat counting (HBC) performance of 48 individuals with their heartbeat detection (HBD) performance. The HBC task required participants to report the numbers of heartbeats counted during brief signaled periods and indexed cardioceptive accuracy by the difference between the numbers of reported and actual heartbeats. In the HBD task, participants indicated the temporal location of heartbeat sensations relative to the onset of ventricular contraction. On each trial, they judged whether heartbeat sensations were or were not simultaneous with brief tones presented at one of six fixed delays following R waves of the ECG. In this method, cardioceptive accuracy or precision was indexed by variability in the temporal locations, relative to the R wave, of tones judged to be simultaneous with heartbeat sensations. Although intratask correlations indicated that each method yielded reliable scores, intertask correlations showed that HBC scores were unrelated to HBD scores. These results, which indicate that heartbeat detection and heartbeat counting are distinct processes, raise important questions about the assessment of interoceptive sensitivity and the involvement of this attribute in the psychological processes that have been associated with it on the basis of their correlations with HBC performance.

Towards a psychophysics of interoceptive processes: the measurement of heartbeat detection.

It is difficult to collect objective evidence of interoception. Unlike exteroception, the effective stimuli for interoception are often unknown, and even when identifiable, they are difficult to control experimentally. Furthermore, direct stimulation of the interoceptors is seldom appropriate in human experimentation. Hence, non-invasive behavioural measures of accuracy in heartbeat detection have frequently been adopted to index interoceptive sensitivity. However, there has been little standardization and the two most popular methods for assessing heartbeat detection, heartbeat tracking and two alternative forced choice methods, appear to be biased and of questionable validity. These issues do not arise with other methods that are based on classical psychophysics and that enable subjects to indicate when during the cardiac cycle their heartbeat sensations occur. Not only are these classical methods highly reliable, but they also provide continuous unbiased measures of the temporal locations of heartbeat sensations and the precision with which these sensations are detected.This article is part of the themed issue 'Interoception beyond homeostasis: affect, cognition and mental health'.

Effects of heartbeat feedback on beliefs about heart rate and heartbeat counting: a cautionary tale about interoceptive awareness.

Heartbeat counting improves after exposure to heartbeat feedback either because feedback trains individuals to detect heartbeats or updates their knowledge/beliefs about heart rate. These possibilities were examined by assessing heartbeat counting, in different postures and following exercise, before and after exposure to immediate and delayed heartbeat feedback. Immediate and delayed feedback provided accurate information about heart rate and, therefore, either could update beliefs about heart rate. However, only immediate feedback marked each ventricular contraction and, thereby, could train participants to detect the beating of the heart by focusing attention on relevant internal sensations. Exposure to immediate and delayed feedback resulted in similar, significant increases in the accuracy of heartbeat counting, indicating that the feedback effect was mediated by non-sensory processes rather than by training participants to detect heartbeat sensations. The current findings demonstrate that the heartbeat counting task is not a valid method to assess cardioception.

Somatosensory amplification and its relationship to heartbeat detection ability.

OBJECTIVE: Somatosensory amplification has been defined as the tendency to experience normal bodily sensations as intense, noxious, and disturbing. The present experiment investigated whether this tendency is due to heightened physiological sensitivity to bodily sensations. METHODS: The relationship between Somatosensory Amplification Scale (SSAS) scores and objective measures of the ability to detect bodily (ie, heartbeat) sensations derived from the Method of Constant Stimuli procedure was assessed. Although somatosensory amplification characterizes hypochondriacs, the relationship between somatosensory amplification and sensitivity to bodily sensations was examined in nonhypochondriacal, nonpatient participants in an effort to dissociate somatosensory amplification from other variables associated with hypochondriasis and/or patient status. RESULTS: Heartbeat detectors were found to exhibit significantly lower SSAS scores than nondetectors. CONCLUSION: This finding suggests that somatosensory amplification is not due to heightened sensitivity to bodily sensations.