Acoustic and intelligibility characteristics of sentence production in neurogenic speech disorders

The purpose of this study was to examine the relationship between scaled speech intelligibility and selected acoustic variables in persons with dysarthria. Control speakers and speakers with amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) produced sentences which were analyzed acoustically and perceptually. The acoustic variables included total utterance durations, segment durations, estimates of the acoustic vowel space, and slopes of formant transitions; the perceptual variables included scaled speech intelligibility and severity of speech involvement. Results indicated that the temporal variables typically differentiated the ALS group, but not the PD group, from the controls, and that vowel spaces were smaller for both neurogenic groups as compared to controls, but only significantly so for the ALS speakers. The relation of these acoustic measures to scaled speech intelligibility is shown to be complex, and the composite results are discussed in terms of sentence vs. single-word intelligibility estimates and their underlying acoustic bases.