Developmental aspects of American English diphthong trajectories in the formant space

Abstract

Formant trajectories of five American English diphthongs embedded in the target words BAIT (/ei/), BITE (/ai/), POUT (/au/), BOAT (/Ou/), BOYS (/oi/) are investigated in the F1-F2 space as a function of age and gender. Age range considered is from 5 to 18 years. In this report, the focus is given to the differences in position between the start/end points of diphthongs and nine monophthons. Averaged formant data across subjects in each age group are examined for the purpose. Two findings are worth mentioning. Firstly, across all age groups, the start and end positions of diphthongs hardly match with the monophthongs that are typically used to transcribe the diphthongs across all age groups (c.f., Holbrook and Fairbanks, 1962). For instance, the start position of /ei/ is very close to /I/ than to /e/, and the end points of /ei, ai, oi/ are significantly different with respect to each other. Secondly, in addition to the areas of vowel space, an overshoot trend toward the nominal end points of diphthongs is the most prominent developmental trend. That is, formant values of diphthongs produced by younger age children are closer to the nominal monophthongs used to transcribe the diphthongs. © 2013 Acoustical Society of America.