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'.

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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.

After practice in judging the simultaneity of brief visual and auditory stimuli, 32 subjects were examined on a heartbeat discrimination procedure in which tones were presented at intervals of 0, 100, 200, 300, 400, or 500 ms following each R‐wave. On each of 60 trials spread over two sessions, tones presented at these intervals could be inspected as frequently and for as long as subjects wished before reaching a decision on which interval yielded stimuli that were coincident with heartbeat sensations. The group as a whole judged tones that were 200–300 ms after the R‐wave to be most contiguous with heartbeat sensations. Although some subjects showed modal preferences for the 100‐ms and 400‐ms intervals, none preferred the 0‐ms or 500‐ms intervals. During each trial subjects inspected preferred intervals more frequently and for longer than non‐preferred intervals. Although interval preferences tended to be stable over the two sessions, preferences were less variable during the second session than during the first session. Furthermore, the number of intervals examined and the duration of each interval examination decreased significantly from Session 1 to Session 2 indicating the development of recognition criteria for heartbeat‐coincident tones.