Effects of Lexical and Somatosensory Feedback on Long-Term Improvements in Intelligibility of Dysarthric Speech

Abstract

Purpose Intelligibility improvements immediately following perceptual training with dysarthric speech using lexical feedback are comparable to those observed when training uses somatosensory feedback (Borrie & Schäfer, 2015). In this study, we investigated if these lexical and somatosensory guided improvements in listener intelligibility of dysarthric speech remain comparable and stable over the course of 1 month. Method Following an intelligibility pretest, 60 participants were trained with dysarthric speech stimuli under one of three conditions: lexical feedback, somatosensory feedback, or no training (control). Participants then completed a series of intelligibility posttests, which took place immediately (immediate posttest), 1 week (1-week posttest) following training, and 1 month (1-month posttest) following training. Results As per our previous study, intelligibility improvements at immediate posttest were equivalent between lexical and somatosensory feedback conditions. Condition differences, however, emerged over time. Improvements guided by lexical feedback deteriorated over the month whereas those guided by somatosensory feedback remained robust. Conclusions Somatosensory feedback, internally generated by vocal imitation, may be required to affect long-term perceptual gain in processing dysarthric speech. Findings are discussed in relation to underlying learning mechanisms and offer insight into how externally and internally generated feedback may differentially affect perceptual learning of disordered speech.