Tone and vowel disruptions in Mandarin aphasia and apraxia of speech

In this study, we investigated the lexical tones and vowels produced by ten speakers diagnosed with aphasia and coexisting apraxia of speech (A-AOS) and ten healthy participants, to compare their tone and vowel disruptions. We first judged the productions of both A-AOS and healthy participants and classified them into three categories, i.e. those by healthy speakers and rated as correct, those by A-AOS participants and rated as correct, and those by A-AOS participants and rated as incorrect. We then compared the perceptual results for the three groups based on their respective acoustic correlates to reveal the relations among different accuracy groups. Results showed that the numbers of tone and vowel disruptions by A-AOS speakers occurred on a comparable scale. In perception, approximately equal numbers of tones and vowels produced by A-AOS participants were identified as correct; however, acoustic parameters showed that, unlike vowels, the patients' tones categorised as correct by native Mandarin listeners differed considerably from those of the healthy speakers, suggesting that for Mandarin A-AOS patients, tones were in fact more disrupted than vowels in acoustic terms. Native Mandarin listeners seemed to be more tolerant of less well-targeted tones than less-well targeted vowels. The clinical implication is that tonal and segmental practice should be incorporated for Mandarin A-AOS patients to enhance their overall motor speech control.