Age vectors vs. axes of intraspeaker variation in vowel formants measured automatically from several English speech corpora

To test the hypothesis that intraspeaker variation in vowel formants is related to the direction of diachronic change, we compare the direction of change in apparent time with the axis of intraspeaker variation in F1 and F2 for vowel phonemes in several corpora of North American and Scottish English. These vowels were measured automatically with a scheme (tested on hand-measured vowels) that considers the frequency, bandwidth, and amplitude of the first three formants in reference to a prototype. In the corpus data, we find that the axis of intraspeaker variation is typically aligned vertically, presumably corresponding to the degree of jaw opening for individual tokens, but for the North American GOOSE vowel, the axis of intraspeaker variation is aligned with the (horizontal) axis of diachronic change for this vowel across North America. This may help to explain why fronting and unrounding of high back vowels are common shifts across languages.