Infant-directed speech of Australian English mothers and fathers: a high and variable pitch with a more breathy and less creaky voice quality

Adults spontaneously speak differently to infants, in Infant-Directed Speech (IDS), compared to Adult Directed Speech (ADS). Key acoustic characteristics of IDS are the increased utterance-level pitch measures, specifically an increased mean or median, minimum, maximum and range. Lesser-studied characteristics of IDS include increased variability in utterance-level F0 across an interaction and a breathier voice quality. Moreover, while there is an abundance of literature on mothers' IDS, there is still limited understanding of fathers' IDS. To address these gaps in the literature, this study compared utterance-level pitch properties, across-conversation pitch variability and voice quality of Australian English mothers' and fathers' IDS, compared to ADS. The final study sample consisted of eight Australian English mother-father dyads and their infant (6-12 months). IDS was elicited from parent-infant dyads during play with toys, and ADS was elicited from mother-father dyads during a play task. The IDS and ADS elicitation tasks were closely matched, maintaining consistency in interlocutor familiarity and the type of activity engaged in by dyads, thus isolating the effect of the infants' presence on both mothers' and fathers' speech. Audio recordings were segmented into utterances and perceptually coded for the presence of whispered speech, and breathy and creaky voice. Utterance-level pitch measures, the standard deviation of utterance-level F0, and the prevalence of voice quality types, were compared across parent genders and registers. Both mothers and fathers increased all utterance-level pitch measures as well as acrossconversation pitch variability in IDS, compared to ADS. Both parent genders, and especially mothers, decreased their creakiness and increased their breathiness in IDS, compared to ADS. These results are discussed in relation to methodological choices, including measures of pitch and voice quality, automated coding in acoustic analyses and task-design considerations -- abstract.