A controlled single-case treatment of severe long-term selective mutism in a child with mental retardation.

The aim of the present study was to demonstrate the efficacy of combining two operant learning procedures--shaping and fading--for treating selective mutism. The participant was a 12-year-old boy with mental retardation presenting a severe long-term selective mutism. The treatment was aimed at increasing the loudness of his vocalizations in an increasingly social milieu. The treatment was conducted over the course of about 20 weeks, with four 15-minute sessions per week. A gradual increase in speech loudness was observed. Data indicated a close correspondence between the changes in speech loudness and the criteria for reinforcement successively applied by the therapist, thereby confirming the causal link between the child's progress and the changes in reinforcement contingencies. In addition, good generalization was noted during the stimulus fading phase. Six-month follow up showed that loudness of verbalizations was still satisfactory in the classroom despite a change of school and peer group. The impressive improvement of the child's verbal behavior shows that the implementation of a treatment package including both shaping and stimulus fading is a worthwhile therapeutic option, even in the case of severe long-term selective mutism associated with mental retardation.