Changes in vowel space characteristics during speech development based on longitudinal of measurements of formant frequencies

During speech development, a child’s vocal tract undergoes changes due to growth of anatomic structures. Such changes typically lower the formant frequencies, reshaping the [F1,F2] vowel space. Much of what is known about vowel space change, however, is based on cross-sectional formant measurements averaged over children in various age groups. The purpose of this study was to characterize changes in the vowel space of four children between the ages of 2 and 6 years. Longitudinally-collected audio recordings of four children (2F,2M) were selected from the Arizona Child Acoustic Database. Each child had been recorded every four months from ages 2-6 years, and produced a variety of words, phrases, vowel-vowel progressions, and occasional spontaneous speech. Formant frequencies (F1 and F2 only) were measured from the recordings using a spectral filtering technique. At each age increment, the formant frequencies for each child were plotted as vowel space density, where the “density” dimension indicates the relative tendency of a talker to produce sound in particular region of the vowel space. The change in location and shape of the density cloud during this period of development will be demonstrated. [Research supported by NIH R01-DC011275, NSF BCS-1145011.]