We investigated how the properties of Infant Directed Speech (IDS) and Adult Directed Speech (ADS) differed in acoustics and in speech-related articulation. Both the degree to which auditory and motion properties changed as a function of speech style (IDS vs. ADS) as well as how the correlation between properties was affected by this change were examined. The acoustic properties of 13 sentences uttered by six mothers either to their infant or to an adult and the corresponding 3D motion of face and head markers were measured. Mean speech duration was longer and mean pitch higher for IDS; the IDS vowel space was also expanded compared to ADS; and all face and head motions were greater in IDS. Moderate correlations were found between speech acoustics and face and head motion. These correlations were consistently larger for ADS compared to IDS.

Index Terms: Infant Directed Speech; Auditory-Visual speech