Articulatory and phonological aspects of consonant substitutions in apraxia of speech.

The articulatory and distinctive features in 825 consonant substitutions produced by nine subjects with apraxia of speech were analyzed. The articulatory and distinctive features of the target consonants were retained beyond chance levels. The substitution patterns observed were very systematic in that more substitutions were made in the initial word position and stops, alveolars, and voiced consonants were used most often as substitutes for target consonants. The retention and usage of the features in the substitutions were closely related to the phonological markedness of the features, Most of the markedness changes were from marked-to-unmarked. The relationships between distinctive features and their markedness suggest that apraxia of speech is primarily a phonological disorder that is manifested in articulatoriy changes. It appears therefore that speakers with apraxia of speech systematically reduce linguistic complexity and simplify the production of consonants. In addition, the substitutions made in apraxia of speech are similar to those made by children.