Rhotic Generalization Is More Rapid in Biofeedback Than Motor-Based Treatment for Residual Speech Sound Disorder: Secondary Outcomes of a Randomized Controlled Trial

PURPOSE: This study examined the effects of visual biofeedback approaches and nonbiofeedback motor-based treatment on generalization outcomes following speech therapy for children with residual speech sound disorders (RSSDs). METHOD: A total of 108 children aged 9-15 years with RSSD affecting American English /ɹ/ were randomly assigned to receive 19 motor-based speech treatment sessions, with or without visual biofeedback (divided into ultrasound or visual-acoustic biofeedback). The treatment included practice designed to implement several motor learning principles, with task difficulty systematically adjusted based on the child's performance. Children's /ɹ/ accuracy on untreated words before and after treatment was rated as correct or incorrect by lay listeners who were blinded to participant characteristics, treatment conditions, and time points. RESULTS: The mixed-effects regression model revealed a statistically significant interaction between treatment type and time point. Specifically, both the biofeedback and nonbiofeedback motor-based treatment groups made progress over time, but the amount of generalization to untreated words was significantly greater in the biofeedback condition than in the motor-based treatment. In a subanalysis comparing biofeedback types, greater generalization was observed following ultrasound biofeedback than visual-acoustic biofeedback, although this effect was strongest at one treatment site. DISCUSSION: This randomized controlled trial found that adding biofeedback to motor-based treatment can increase the rate of accurate production of the American English /ɹ/ in untreated words.