Factors Influencing the Effects of Delayed Auditory Feedback on Dysarthric Speech Associated with Parkinson ’s Disease

Abstract

Purpose: The present study examined the effects of Delayed Auditory Feedback (DAF) as a rate control intervention for dysarthric speakers with Parkinson's disease. Adverse reactions to relatively long delay intervals are often observed during clinical use of DAF, and may result from improper "matching" of the delayed signal. To facilitate optimal use of DAF, clinicians may need to provide instruction, modeling, and feedback. Therefore, the primary purpose of this 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. Method: Three males with Parkinson's disease and an associated dysarthria served as participants in this singlesubject study. The A phases consisted of a sentence reading task using DAF; the B phases incorporated clinician instruction. 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 were speech rate, percent intelligible syllables, and percent disfluencies. Results: Results indicated that for all three speakers, DAF significantly reduced reading rate and produced significant improvements in either intelligibility (Speaker 3) or fluency (Speakers 1 and 2). A delay interval of 150 ms produced the greatest reductions in reading rates for all speakers, although any DAF setting used was sufficient to produce significant improvements in either intelligibility or fluency. Additionally, supplementing DAF with clinician instruction resulted in significantly enhanced gain achieved with DAF. Conclusions: These findings demonstrated the effectiveness of various intervals of DAF in improving speech deficits associated with Parkinson's disease; particularly when patients are provided with instruction, modeling and feedback by the clinician.