Properties of Relative Timing and Phonetic Complexity in Adults with Dysarthria Secondary to Amyotrophic Lateral Sclerosis

Introduction: This study examined the relative timing in individuals with dysarthria secondary to amyotrophic lateral sclerosis (ALS). The aim was to examine whether the relative timing was influenced by severity of dysarthria and phonetic complexity of the speech being produced. Methods: Twenty-one adults with dysarthria secondary to ALS, who presented with a range of dysarthria severity, participated in the study. A group of nonimpaired, age-matched adults served as controls. All participants produced a single phrase, across which four measures of relative timing were calculated, and the phonetic composition (complexity) of each measure was considered. Both participant groups completed the Sentence Intelligibility Test, which provided measures of speech intelligibility and speaking rate. Results: Relative timing did not significantly differ between speaker groups across the four measures, regardless of phonetic complexity. Neither Sentence Intelligibility Test score nor speaking rate were significantly correlated with relative timing. Discussion: Relative timing of phrase-level speech appears to remain intact regardless of the phonetic complexity of speech among individuals with dysarthria secondary to ALS. The potential of an internal phonological system organizing speech gestures is discussed to explain why the consistency in relative timing occurs.