An Explanatory Model of Speech Communication Centered on Multiscale Rhythmic Modulation: Implications for Motor Speech Assessment and Intervention for Individuals With Amyotrophic Lateral Sclerosis.

Purpose: This study proposed an explanatory model of speech communication centered on multiscale rhythmic modulation to inform motor speech assessment and management. To these ends, a fit-for-purpose, automated measurement tool was used to evaluate and/or cross-validate (a) the previously reported effect of a neuromotor disorder--amyotrophic lateral sclerosis (ALS)--and (b) the effects of two cueing strategies, commonly used in managing motor speech disorders, on rhythmic modulation of speech. Method: A secondary analysis was carried out on the X-ray Microbeam database. The analyzed data included the articulatory--kinematic and acoustic recordings of a phonetically loaded sentence produced by 19 individuals with ALS and 23 neurologically healthy controls in one habitual style and two nonhabitual styles as elicited by the slow and clear speech cues, respectively. The measurement tool quantified the modulation patterns of four articulators as well as four critical-band and one wide-band envelopes at three linguistically relevant timescales (delta, theta, beta/gamma) to assess rhythm control at the prosodic, syllabic, and subsyllabic levels. To address the research aims, the disease and speaking style effects on all modulation metrics were evaluated. Results: For Aim 1, speakers with ALS showed reduced modulation depth of multiple articulators and critical-band envelopes at all timescales. For Aim 2, the slow speech cue elicited changes in articulatory modulation at multiple timescales, globally enhancing the control of all and especially syllabic and subsyllabic rhythms in speakers with ALS. Clear speech primarily elicited changes in articulatory modulation at the theta timescale, generating a more restricted effect on syllabic rhythm. Conclusions: The findings generally aligned with our prior research, supporting the robust utility of the measurement tool for assessing rhythmic disturbances of speakers with ALS. Moreover, this tool showed promise for delineating cueing-elicited changes in rhythmic modulation of speech, which has potential implications in tailoring and evaluating the outcomes of behavioral intervention. [ABSTRACT FROM AUTHOR]