An acoustic study of vowel production in aphasia

A group of five anterior and seven posterior aphasic patients were recorded for their vowel productions of the nine nondipthong vowels of American English and compared to a group of seven normal speakers. All phonemic substitutions were eliminated from the data base. A Linear Predictive Coding (LPC) computer program was used to extract the first and the second formant frequencies at the midpoint of the vowel for each of the remaining repetitions of the nine vowels. The vowel duration and the fundamental frequency of phonation were also measured. Although there were no significant differences in the formant frequency means across groups, there were significantly larger standard deviations for the aphasic groups compared to normals. Anterior aphasics were not significantly different from posterior aphasics with respect to this greater formant variability. There was a main effect for vowel duration means, but no individual group was significantly different from the other. Standard deviations of duration were significantly greater for the anterior aphasics compared to normal speakers, but not significantly different from posterior aphasics. Posterior aphasics did not have significantly greater standard deviations of duration than did normal subjects. Greater acoustic variability was considered to evidence a phonetic production deficit on the part of both groups of aphasic speakers, in the context of fairly well-preserved phonemic organization for vowels.