Consistency of voice produced by patients with adductor spasmodic dysphonia: a preliminary investigation.

Adductor spasmodic dysphonia (ADSD) is an idiopathic focal laryngeal movement disorder causing involuntary and uncontrollable spasms in the vocal fold musculature, primarily during voice onset. Although phonatory instability has been reported through clinical observation and empirical study, no examination of phonatory performance consistency in ADSD has been done. Phonatory instability refers to phonatory unsteadiness and has been previously defined by the presence of acoustic aberrations during speech. Performance consistency pertains to variations in these phonatory aberrations across repeated trials or over time. This study focused on the phonatory performance consistency of those with ADSD by using three acoustic measures of phonatory instability. Twenty patients with ADSD were recorded during three trials of reading a standard passage. Eight of the 20 patients were recorded twice during two separate recording sessions held approximately 6 months apart. The number of phonatory breaks, frequency shifts, and aperiodic segments were the dependent measures. Data were subjected to inferential statistical analysis to test for significant differences among the measures in two conditions: across three trials produced within one recording session and across multiple trials produced during two distinct recording sessions. No significant differences were found for any of the measures either as a function of trials recorded on the same day or across the two recording sessions. The data suggest a need for describing phonatory instability and performance consistency as separate entities with regard to neurological voice disorders.