Behavioral and Psychophysiological Responses of 4-month-old Infants to Differing Rates of Infant Directed Speech

Infants of various ages across the first postnatal year have shown behavioral preferences (i.e., more attention) to visual displays when looking resulted in the presentation of Infant-Directed Speech (IDS) compared to Adult-Directed Speech (ADS). Although IDS differs from ADS on a variety of measures, most research has focused on various pitch characteristics (i.e., IDS is higher in absolute pitch and more variable in pitch across utterance length). Work from our lab has found that when the pitch characteristics of IDS were held constant, but the temporal features were manipulated, younger (but not older) infants attended more to slower rates of IDS, even though it was unlikely that they had heard such speech (when speech is spoken at this slow rate, the fundamental frequency cannot be maintained). The purpose of this study was to expand our investigation of how speaking rate affects infant attention by adding the physiological measure of heart rate to our protocol. Of specific interest was whether infants would show differential amounts of heart-rate (HR) decelerations as a function of rate (i.e. greater decelerations to slowed speech). 4-month-old infants were tested with normal IDS (unaltered rate) and slow IDS (rate was twice as slow as normal). Behaviorally, infants did not differentially attend to a display as a function of speech type. Psychophysiologically, infants showed more pronounced HR decelerations to slow than to normal IDS. The discrepancy between measures of attention is discussed, especially with regard to the organization of attention in infants of this age.