Vowel quality in aphasia and apraxia of speech: Phonetic transcription andformant analyses

We examined acoustic and perceptual features of vowel quality in aphasia an d apraxia of speech. Twenty aphasic speakers with and without apraxia of sp eech and ten normal speakers produced the words "hid'' and "head'' approxim ately 24 times. Each production was transcribed with broad phonetic transcr iption, and the first and second formant frequencies were measured at the m idpoint of the vowel steady state. According to the phonetic transcription, some aphasic and apraxic speakers displayed a large number of vowel substi tutions, whereas others were indistinguishable from normal speakers. Percei ved substitutions were generally close to the target and affected almost ex clusively vowel height rather than vowel frontness. Acoustically, several s peakers in both aphasic groups displayed a formant pattern that deviated fr om normal. The nature of the deviation pattern varied across individual aph asic and apraxic speakers. For some, formant frequencies were abnormally va riable, whereas others displayed a pattern of only occasional deviations, a nd yet others demonstrated a collapsing of phonetic categories. The results are consistent with previous reports that articulatory positioning for vow els is impaired in many aphasic and apraxic speakers. The existence of indi vidual articulatory patterns is emphasised, and the limitations of a static approach to formant analysis are noted.