Measuring the dispersion of density in head and neck cancer patients' vowel spaces: The vowel dispersion index
The present study introduces a measure of the dispersion of density throughout the vowel space, which we refer to as the vowel dispersion index. The vowel dispersion index is based on calculating the total variation of the density values in Story & Bunton’s (2017) convex hull representation of vowel space density. Overall, the vowel dispersion index quantifies how much change there is throughout the vowel space density. When the value is low, the speaker tends to produce most of their vowels in a central location like /?/, often characteristic of hypoarticulated or reduced speech. When the value is high, the speaker often spreads their vowel productions throughout the vowel space, as is characteristic of hyperarticulation. The vowel density index is calculated and analyzed for a small sample of recordings from head and neck cancer patients at different stages pre- and post-surgery. Consideration is given to 1) how the index corresponds with visual analysis of their vowel space density and 2) what the dispersion of density throughout the vowel space suggests about the communication strategies these patients employ while speaking. The vowel density index generally corresponds with visual impressions of the vowel space density. Additionally, the patients are overall found to employ hyperarticulation strategies to increase the clarity of the information in their speech post-surgery. These findings are discussed with respect to phonetic theory, principally, Lindblom’s (1990) H&H theory.
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