Quadratic trend analysis and heartbeat detection.

In heartbeat detection tasks based on the Method of Constant Stimuli (MCS), subjects judge the simultaneity between their heartbeats and stimuli presented at six intervals ranging from 0 to 500 ms after the R-waves on an electrocardiogram. Because research suggests that subjects do not perceive stimuli at 0 or 500 ms as simultaneous, individual performance was indexed with quadratic trend analysis to test for distributions of simultaneity judgments across intervals that peak between 0 and 500 ms. Further, because some tasks use only two intervals, performance was also indexed using intervals of either 0 and 200 ms or 200 and 500 ms. Continuous performance scores from quadratic trend and two-interval analysis tended to correlate more highly with variables previously shown to correlate with heartbeat detection than scores from the commonly-used chi(2) analysis. These findings support the use of both quadratic trend analysis and two-interval tasks for assessing heartbeat detection ability.