Short-latency acceleration of human heart rate as a function of stimulus intensity

The study examined the effectiveness of three intensities of white noise in evoking short-latency acceleration of human heart rate. 3 groups of 10 female subjects were presented with 1-sec. bursts of white noise with virtually instantaneous rise times at intensities of 100 db (re 20 mu N/m2), 90 db, or 80 db SPL as measured at the headset. 5 bursts were presented at intervals of 45 sec. while the EKG was recorded. An increase in heart rate during poststimulus beats 3 and 4 compared with the mean rate of the three beats prestimulus was reliably evoked on the first two trials in the 100-db and 90-db groups but not in the 80-db group. Apart from a recovery of acceleration on Trial 5 for the 100-db group, the 100-db and 90-db groups did not differ in amplitude or rate of habituation of the response. Poststimulus heart-rate level was not significantly related to prestimulus level as expected in terms of the law of initial values. The results were interpreted as consistent with F.K. Graham's interpretation of short-latency cardiac acceleration as a component of startle.