The Influence of Linguistic Demand on Symptom Expression in Adductor Spasmodic Dysphonia

Abstract

Adductor Spasmodic Dysphonia (ADSD), a form of focal dystonia, has been defined as a neurogenic, task-specific disorder characterized by abrupt spasms of intrinsic laryngeal muscles that result in phonatory breaks. Voice breaks are typically isolated to propositional speech, and reported to increase in severity as speaking demand or complexity increases. Research to date has focused on variations in phonologic contexts and their influence on voice breaks. The influences of variables at lexical and syntactic levels of analysis have been less well-researched and yet may provide insight into observed variability of symptom manifestation in this rare voice disorder. This study investigated frequency of voice breaks over 20 standard sentences in 38 individuals with ADSD according to linguistic complexity measures including lexical density and a four-level lexical frequency and type paradigm. Two research questions about linguistic influences and ADSD symptom manifestation were posed: (1) does the frequency of voice breaks vary according to the lexical density of a string? and (2) does the frequency of voice breaks vary according to a measure of lexical frequency/type? Results revealed a nonsignificant relationship between string length and voice break frequency, whereas a significant relationship was found between lexical density and voice break frequency (P = 0.029, r = 0.488). Lexical analysis results revealed a significant relationship between lexical frequency and voice breaks, with words within technical/academic classes relating to the highest rates of voice break across 38 subjects with ADSD. Results from this secondary analysis provide support for the hypothesis that variation in linguistic demand may modulate symptom expression in SD. Specifically, lexical density and lexical frequency modulated the frequency of symptom expression in classic forms of SD in this purposive sample.