Acoustic characteristics of diphthongs in Parkinson's disease

Abstract

The second formant frequency (F2) is sensitive to dysarthria. For example, vowel F2 slope has been shown to correlate with intelligibility, such that persons who are less intelligible or who have more severe speech impairment also tend to have shallower F2 slopes (Weismer etal., 1992). This result is consistent with studies suggesting the perceptual importance of transitions (Hillenbrand and Nearey, 1999), although the extent to which F2 slope explains reduced intelligibility in dysarthria is unclear. F2 slope also may serve as an acoustic metric of effort (Moon and Lindblom, 1994; Wouters and Macon, 2002). Therapeutic techniques for dysarthria, including Clear and Loud speech, are thought to be beneficial because they involve a scaling up of effort. Clear speech emphasizes hyperarticulation or increased articulatory effort, while Loud speech focuses on increasing respiratory–phonatory effort, although it has been suggested that increased loudness involves a system-wide scaling up of effort (Fox etal., 2006). Empirical evidence that Clear or Loud speech is associated with increased articulatory effort in dysarthria is limited. The current study sought to further evaluate this suggestion by investigating F2 slope characteristics for vowels produced in Habitual, Clear and Loud conditions by individuals with dysarthria secondary to Parkinson's disease.