Some phonemic characteristics in apraxia of speech

The articulatory performance of 13 left hemisphere-damaged adults who presented apraxia of speech was tabulated on confusion matrices and analyzed according to error pattern. Consonants were more susceptible to error than were vowels, as were consonant clusters when compared to single consonants. No significant differences existed among error percentages for the intial, medial, and final positions. When errors were analyzed according to manner of production, affricatives and fricatives were significantly more susceptible to error than all others. Analysis of errors according to place of production revealed lingua alveolar and bilabial phonemes to be significantly less impaired than all other categories. No differences were found in error percentages of voiced and unvoiced phonemes. The sequential nature of substitution errors was further analyzed by tallying and classifying errors as anticipatory (prepositioning), reiterative (postpositioning), or metathesis. Seven percent of the substitution errors in this study were sequential, with anticipatory errors outnumbering reiterative errors by a ratio of 6 to 1. Feature analysis of substitutions to determine distance from the target sound revealed that 38% of the substitutions were defective in two or more features. Some of these subjectively bore little resemblance to the target sound.