Rate and intensity effects in multiple sclerosis

By K. Tjaden, A. Fox and A. Ludwig


            Improved understanding of how variations in speech rate and vocal intensity impact vocal tract acoustic output and perceptual impressions of speech would help to provide a stronger scientific basis for certain clinical treatment techniques.  The current study examined the effects of slowed speaking and increased vocal intensity on the acoustic vowel space for 14 individuals with Multiple Sclerosis (MS) and healthy controls.  Participants with MS typically presented with ataxic or spastic dysarthria.  Vowel space area was studied given research suggesting a relationship between the size of the acoustic vowel space and perceptual impressions of speech severity.  Participants produced target words containing the corner vowels in a carrier phrase task.  Target words also were produced in a paragraph reading task. Vowel space area measures were computed from F1 and F2 measures obtained at the temporal midpoint of corner vowels. Preliminary results suggest a tendency for reduced vowel space areas in the MS group.  In addition, although vowel space areas tend to be smallest in the Normal Condition, average measures were unaffected by speaking conditions and thus, are at odds with studies suggesting an expansion of the acoustic vowel space with slowed rate or increased intensity. Additional analyses will focus on speech task and individual speaker differences.