Temporal Arrangement of Signals in Heartbeat Discrimination Procedures

ABSTRACT Three experiments are reported which were designed to define optimal placements of S+ signals in Whitehead‐type discrimination procedures by asking when in the cardiac cycle signals are perceived as most coincident with heartbeats. In Experiment I subjects discriminated signals delayed either 0 or 100 ms from the R‐wave from signals delayed 400 ms. In Experiment II subjects chose signals delayed 0, 100, or 200 ms as more synchronous with heartbeats than signals delayed 300 or 400 ms. In Experiment III no central tendency emerged when subjects adjusted a signal through delays of 0, 60, 120, 180, and 240 ms seeking the value most synchronous with heartbeats. It is concluded that subjects can reliably discriminate events in the first quarter second of the cardiac cycle from events occurring later (although the functional significance of this ability remains obscure) and that S+ signals in such procedures should be placed within that time period.