The vowel lengthening exaggeration effect in speakers with apraxia of speech: Compensation, artifact, or primary deficit?

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Abstract
Vowel duration functions contrastively in English to signal the voicing feature of syllable-final stop consonants. This study examines three hypotheses posited to explain why speakers with apraxia of speech and a concomitant aphasia exhibit an exaggerated vowel lengthening effect relative to speakers with dysarthria, aphasia without apraxia and controls. The investigation addresses the hypotheses that the vowel lengthening exaggeration effect is attributable to: (1) a compensatory strategy, (2) an artifact of slow speaking rate, (3) the concomitant language impairment, or (4) a primary deficit reflecting the underlying nature of the apraxia disorder. The results do not support the first three of these hypotheses. It is hypothesized that the temporal measures most likely to reveal abnormalities which are uniquely characteristic of speakers with apraxia of speech are those which are relational in nature, either with respect to inter-articulator timing or contrastive durations.