PSYCHOPHYSIOLOGICAL AND BEHAVIORAL RESPONSIVITY TO TEMPORAL PARAMETERS OF ACOUSTIC STIMULI

In Experiment 1, a total of 86 infants, 42 three-month-olds and 44 six-month-olds, participated. Two important parameters of speech were manipulated: (a) duration of the interphonemic transition of a diphthong and (b) duration of interstimulus interval (pulsed vs. continuous presentation). Heart rate (HR) and body movement (BM) were recorded. The results showed that neither 3- nor 6-month-old infants responded with differential HR pattern to interphonemic transition; however, both 3- and 6-month-old infants responded with a significantly larger HR deceleration to pulsed versus continuous pattern of presentation. Compared to the 3-month-olds, 6-month-old infants exhibited a larger response to the pulsed stimuli. This suggests that in contrast to previous studies showing attenuation of HR deceleration to pulsed stimuli with increased age, stimulus complexity may be an important consideration. Despite BM deceleration with stimulus onset, BM response pattern did not differ for either stimulus parameter, although 6-month-olds exhibited a larger BM deceleratory response. In Experiment 2, 80 three-month-old infants were presented with a discrimination task to determine whether the absence of differential responding to interphonemic transition in Experiment 1 was due to an inability to discriminate the selected interphonemic transition durations. The results showed that interphonemic transition was discriminable regardless of pattern of stimulus presentation (pulsed, continuous).