Cardiac orienting and vowel discrimination in newborns: crucial stimulus parameters.

To delineate the acoustic parameters crucial for eliciting a cardiac deceleratory response in newborns, 2 experiments investigated stimulus dimensions implicated as important by previous research. In experiment 1, the temporal pattern and spectral complexity of moderately intense auditory stimuli influenced the cardiac responses of 24 alert newborns. Temporal pattern determined response direction: pulsed stimuli elicited cardiac deceleration, whereas continuous stimuli elicited acceleration. Stimulus complexity influenced response magnitude: the most complex stimulus, a synthetically produced vowel, produced both the largest deceleration for pulsed stimuli and the largest acceleration for continuous ones. Experiment 2 (N = 16) extended the temporal pattern effect to other vowel stimuli in a no-delay discrimination paradigm. These findings indicate that the cardiac deceleratory response to auditory stimuli is a predictable component of the newborn infant's behavior. Furthermore, they suggest that stimulus parameters that influence cardiac deceleration may also play a critical role in stimulus discrimination.