Factors influencing the efficacy of delayed auditory feedback in treating dysarthria associated with Parkinson\u27s disease

Abstract

Parkinson\u27s disease patients exhibit a high prevalence of speech deficits including excessive speech rate, reduced intelligibility, and disfluencies. The present study examined the effects of delayed auditory feedback (DAF) as a rate control intervention for dysarthric speakers with Parkinson\u27s disease. Adverse reactions to relatively long delay intervals are commonly observed during clinical use of DAF, and seem to result from improper matching of the delayed signal. To facilitate optimal use of DAF, therefore, clinicians must provide instruction, modeling, and feedback. Clinician instruction is frequently used in speech-language therapy, but has not been evaluated during use of DAF-based interventions. Therefore, the primary purpose of the present study was to evaluate the impact of clinician instruction on the effectiveness of DAF in treating speech deficits. A related purpose was to compare the effects of different delay intervals on speech behaviors. An A-B-A-B single-subject design was utilized. The A phases consisted of a sentence reading task using DAF, while the B phases incorporated clinician instruction into the DAF protocol. During each of the 16 experimental sessions, speakers read with four different delay intervals (0 ms, 50 ms, 100 ms, and 150 ms). During the B phases, the experimenter provided verbal feedback and modeling pertaining to how precisely the speaker matched the delayed signal. Dependent variables measured were speech rate, percent intelligible syllables, and percent disfluencies. Three males with Parkinson\u27s disease and an associated dysarthria participated in the study. Results revealed that for all three speakers, DAF significantly reduced reading rate and produced significant improvements in either intelligibility (for Speaker 3) or fluency (for Speakers 1 and 2). A delay interval of 150 ms produced the greatest reductions in reading rates for all three speakers, although any of the DAF settings used was sufficient to produce significant improvements in either intelligibility or fluency. In addition, supplementing the DAF intervention with clinician instruction resulted in significantly greater gains achieved with DAF. These findings confirmed the effectiveness of various intervals of DAF in improving speech deficits in Parkinson\u27s disease speakers, particular when patients are provided with instruction and modeling from the clinician