Vowel space as a tool to evaluate articulation problems

Treatment for oral tumors can lead to long term changes in the anatomy and physiology of the vocal tract and result in problems with articulation. There are currently no readily available automatic methods to evaluate changes in articulation. We developed a Praat script which plots and measures vowel space coverage. The script reproduces speaker specific vowel space use and speaking-style dependent vowel reduction in normal speech from a Dutch corpus. Speaker identity and speaking style explain more than 60% of the variance in the measured area of the vowel triangle. In recordings of patients treated for oral tumors, vowel space use before and after treatment is still significantly correlated. Articulation before and after treatment is evaluated in a listening experiment and from a maximal articulation speed task. Linear models can explain 50-75% of variance in perceptual ratings and relative articulation rate from values at previous recordings and vowel space  measures.