Precision of fricative production in aphasia and apraxia of speech: A perceptual and acoustic study

We examined the precision of fricative place of articulation production in speakers with aphasia and apraxia of speech. Articulatory precision was def ined based on acoustic consistency across repeated productions of the same target words and on the acoustic distinction between similar fricative targ ets. Ten aphasic speakers with apraxia of speech, ten aphasic speakers with out apraxia of speech, and ten normal control speakers produced words begin ning with voiceless alveolar and palatal fricatives. The Bark transformed f irst spectral moment was computed in the middle of the fricative. For norma l speakers, this measure varied little across repetitions and the target fr icatives were clearly distinguished. For aphasic speakers with apraxia of s peech, there was substantial spectral variability and overlap between targe ts. A similar pattern was found for aphasic speakers without apraxia of spe ech, although the effects were smaller in magnitude. Among these aphasic sp eakers, the greatest degree of spectral overlap was seen in speakers with l ow single-word intelligibility scores. The observed spectral imprecision is consistent with impaired phonetic-motor control, not only in the temporal, but also in the spatial domain of speech production.