Temporal pattern and spectral complexity as stimulus parameters for eliciting a cardiac orienting reflex in human fetuses

The purpose of this study was to determine whether temporal pattern and/or spectral complexity were important stimulus parameters for eliciting a card iac orienting reflex (OR) in low-risk human fetuses. Each of 28 term fetuse s was exposed to four sounds formed from the four different combinations of temporal pattern (pulsed, continuous) and spectral complexity (sine wave, /(a) over cap/). The fetal cardiac electrical signal was captured transabdo minally at a rate of 1024 Hz, and fetal R-waves were extracted by using ada ptive signal-processing techniques. We found that pulsed sounds elicited a significantly greater decrease in heart rate (HR) than did continuous sound s. However, the HR response was relatively unaffected by spectral complexit y. For the pure tone and the phoneme used in this study, our results indica te that temporal characteristics were more effective at eliciting a cardiac OR in human fetuses than was spectral complexity.