Fricative production in aphasia: effects of speaking rate

The present study investigated the effects of alterations in speaking rate on the production of the fricatives [f s v z] by 10 nonfluent aphasics, 7 fluent aphasics, and 10 normal control subjects. An examination of fricative consonants allowed us to address whether previous conflicting findings for vowels and stop consonants produced by nonfluent aphasic patients were due to basic differences in the treatment of major sound classes or to differences in the length of the segments under investigation. Acoustic analyses revealed that all subjects were able to manipulate rate of speech. Both groups of aphasic patients produced rate changes that were smaller in magnitude than those of the normal subjects. Further analyses demonstrated that both the fluent and the nonfluent aphasic patients were able to instantiate the rate changes in terms of fricative duration. However, both patient groups exhibited breakdowns in the ability to maintain contrastive differences between voiced and voiceless fricatives, particularly at fast rates of speech. Possible sources of these breakdowns are explored.