Coarticulation in aphasia: Effects of utterance rate and complexity

Abstract

The magnitude and extent of anticipatory coarticulation were examined in groups of fluent and nonfluent aphasic patients, and normal control subjects. Previous investigations have shown inconsistent impairments in coarticulation in aphasic patients; studies have also demonstrated breakdowns in production as rate and complexity increase. One- and two-syllable target utterances were elicited at slow and fast rates of speech with or without a consonant intervening between the target consonant and vowel, and with or without a preceding schwa, to manipulate utterance complexity. Acoustic analyses (F2 and centroid frequencies) revealed that both groups of aphasic patients exhibited relatively normal patterns of anticipatory coarticulation. However, small but significant differences among the groups emerged in certain conditions. Surprisingly, increased utterance complexity was not found to reduce coarticulatory effects to a greater degree in the nonfluent relative to the fluent aphasic group. The ability of listeners to identify the upcoming excised vowel when presented with the target consonant alone was also examined to determine the perceptual salience of the coarticulatory cues. Results are discussed in relation to hypotheses concerning the underlying speech production deficits in fluent and nonfluent aphasic patients and the neural substrate for aspects of speech motor control. [Supported by MRC.]