Overgeneralization in treatment of severe apraxia of speech: A case study

By A. Raymer, M. Haley, and D. Kendall

Individuals with severe apraxia of speech can improve verbalizations with intensive training. However, when phonemes are trained in succession, improvements often overgeneralize to inappropriate untrained contexts. We investigated whether training multiple phonemes concurrently would increase production of trained phonemes with less overgeneralization to untrained contexts. Our subject, HH, had severe apraxia of speech following a large left hemisphere stroke. Prior to treatment, HH produced only stereotypic /w/-initial syllables for most verbal responses. HH received intensive training incorporating motor, tactile, and auditory cueing in a hierarchy from isolated consonant to alternating consonant-vowel syllables for three phonemes, /p, t, k/. In daily probes, we tested his imitation of words incorporating all trained phonemes and untrained /b, d, g, f/. Treatment led to improved imitation for trained /p/ and /t/, and generalization of /p/ to /b/ and /t/ to /d/. No improvements were evident for trained /k/, or untrained /f/ and /g/. Rather, HH produced overgeneralizations of /t/ and occasionally /p/ to these phonemes, particularly for /k/ targets. These findings suggest that training establishes motor patterns which these individuals draw upon in contexts in which they lack an adequate motor program for implementation of the intended phoneme.