Kalashnikova, M. , Carignan, C. & Burnham, D.
The MARCS Institute for Brain, Behaviour and Development, Western Sydney University
When addressing their young infants, parents systematically modify their speech. Such infant-directed speech (IDS) contains exaggerated vowel formants, which have been proposed to foster language development via articulation of more distinct speech sounds. The present study rigorously tested this assumption using both acoustic and, for the first time, fine-grained articulatory measures of IDS and adult-directed speech (ADS). Mothers were recorded speaking to their infant and to another adult, and measures were taken of their acoustic vowel space, their tongue and lip movements, and the length of their vocal tract. Results showed that IDS, but not ADS, contains acoustically exaggerated vowels, and these are not the product of adjustments to tongue or to lip movements. Rather, they are the product of a shortened vocal tract due to a raised larynx, which can be ascribed to speakers? unconscious effort to appear smaller and more non-threatening to the young infant. We propose that this adjustment in IDS may be a vestige of early mother-infant interactions, which had as its primary purpose the transmission of non-aggressiveness and/or a primitive manifestation of pre-linguistic vocal social convergence of the mother to her infant.