The influence of selected phonetic and linguistic variables on articulatory production in apraxic speakers

The purpose of this investigation was to measure how sentence voice, grammatical class, and phonetic complexity influence the articulation of eleven apraxic speakers. A set of nonsense CVC and CCVCC syllables were constructed using phonemes that contained either few or numerous marked distinctive features. These syllables were inserted into the subject, verb, and object function locations of both active and passive voice sentences. Later, the entire sentence was presented to these subjects who were required to repeat the nonsense syllable.

Results suggest that for CVC stimuli, grammatical class, sentence voice, and phonetic complexity disrupted the articulation of apraxic speakers. However, the magnitude of these disruptions were not equal for each variable. Also, none of these three variables appeared to interact with each other, indicating that each factor could have a separate influence on the process of articulation. With CCVCC stimuli, only phonetic complexity produced any adverse affect.

These data can also be interpreted in a different manner. While grammatical class, sentence voice, and phonetic complexity were found to be "statistically significant," it is possible that this significance was discovered due to the removal of the between-subject variance in the statistical model. The result of this action is that small differences between group means may be important only from a statistical viewpoint. From a practical or clinical viewpoint, these differences may be of little importance to the rehabilitative process.

When analyzing individual consonantal errors, it was discovered that apraxic speech is dominated by substitutions, omissions, and additions. Further, the articulatory errors, while being inconsistent, were not unsystematic. The apraxic speakers substituted phonemes with relatively few marked features for those phonemes which contained numerous marked features. Also, a distinctive feature analysis indicated the articulation errors were good approximations of the target phoneme.

It was suggested that the available theories of articulation were not adequate to describe the apraxic productions. A modified version of Roy's model of motor production was presented to account for the small influence of the linguistic and phonetic variables.