Acoustic Space in Motor Disorders of Speech: Two Case Studies

Studies on acoustic space have strengthened the view that vowels are acoustically and perceptually defined in terms of their relative positioning in vowel space. Every speaker identifies an optimal vowel space within which perceptual, phonological contrast is maintained. This is an interdisciplinary study involving speech pathology, physics of speech and neurology of speech. Two case studies of dysarthria presented in this paper are -- one Parkinson's disease and one case of acute ischemic stroke with age-gender-language matched controls. A detailed acoustic analysis shows how acoustic space gets considerably reduced, in both PD and stroke, and in these two very different kinds of dysarthrias the acoustic space is also modified very differently. The study also examines the third formant to show that the higher formants are consistently lowered in both PD and stroke. Hypokinetic speech production in these cases is reflected in lower intensity. The results have significant applications in clinical acoustics and in the theoretical fields of neurology of speech, linguistics and phonology.