Heartbeat Detection: Judgments of the Simultaneity of External Stimuli and Heartbeats

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.