Published online by Cambridge University Press: 13 February 2013
Typically, the point vowels [i,ɑ,u] are acoustically more peripheral in infant-directed speech (IDS) compared to adult-directed speech (ADS). If caregivers seek to highlight lexically relevant contrasts in IDS, then two sounds that are contrastive should become more distinct, whereas two sounds that are surface realizations of the same underlying sound category should not. To test this prediction, vowels that are phonemically contrastive ([i–ɪ] and [eɪ–ε]), vowels that map onto the same underlying category ([æ–] and [ε–]), and the point vowels [i,ɑ,u] were elicited in IDS and ADS by American English mothers of two age groups of infants (four- and eleven-month-olds). As in other work, point vowels were produced in more peripheral positions in IDS compared to ADS. However, there was little evidence of hyperarticulation per se (e.g. [i–ɪ] was hypoarticulated). We suggest that across-the-board lexically based hyperarticulation is not a necessary feature of IDS.
Our deepest appreciation to the families who participated and to Krista Ashmore, Allison Gladfelter, and Kat Montoya for the phonetic coding. Portions of this work were discussed at the 2010 Journees des Etudes sur la Parole, the Acoustical Society of America 2010 November meeting, and the 2011 Testing Models of Phonetics and Phonology Workshop at the University of Colorado at Boulder. We are grateful to these audiences and our colleagues at Purdue University, the Laboratoire de Sciences Cognitives et Psycholinguistique, the University of Pennsylvania, and Northwestern University for helpful discussions; as well as to Titia Benders, two anonymous reviewers, and the editors for insightful comments and careful reading of a previous version of this manuscript. We also thank Kristine H. Onishi for help in the design of the elicitation material. All errors are our own. AS collected the recordings, and supervised the coders; AC generated the coder training materials and performed the acoustical and statistical analyses. Both authors contributed to the writing. This work was supported by funds from NSF 0843959 to Amanda Seidl. AC gratefully acknowledges the financial support of the Fondation Fyssen and Ecole de Neurosciences de Paris.