The cardiac component of the orienting response: effects of signal intensity, clinical interpretation, and procedural limitations.

The effects of stimulus intensity on the cardiac component of the orienting response were explored in male and female subjects. The acoustic stimuli were 10 recorded repetitions of an identical consonant vowel cluster spoken by an adult male. Heart rate data were obtained for both subject groups at three sensation levels across the baseline heart rate and at 10 stimulus presentation trials. A significant main effect was noted for trials. Significant linear and quadratic trend components were observed, reflecting habituation of the orienting response as a function of trials, and indicating the nonmonotonicity of heart rate change over trials. A lower mean heart rate was observed for Condition Two (20 dB SL) than for either of the other conditions, 10 dB and 30 dB SL respectively. Analysis of group variability and individual subjects' heart rate data suggested limitations in generalizing from group to individual data, as well as a need for further investigation if proper interpretation of single subject heart rate data are to be useful in the clinical situation.