Single word intelligibility in aphasia and apraxia of speech: A phonetic error analysis

This study examined the phonetic differences between word productions attempted by aphasic speakers and listeners' perceptions of these productions. Ten speakers with aphasia and apraxia of speech, ten with aphasia only and ten normal speakers produced 70 monosyllabic words. Listeners orthographically transcribed the words they thought the speakers were saying. The target and transcribed words were compared and phonetic differences noted. There was no significant difference in the frequency of target-transcription discrepancies between vowels and consonants or between consonants in prevocalic and postvocalic position for any of the speaker groups. In addition to a greater number of errors, the phonetic error profiles of aphasic speakers with and without apraxia of speech were different from that of normal speakers. Among apraxic speakers, different error patterns were found in speakers with high overall intelligibility than in speakers with low to moderate overall intelligibility. The frequency of errors affecting place of articulation for stops and nasals was highly correlated with overall speech intelligibility. Other common phonetic confusions for the apraxic speakers included confusions between singleton and consonant clusters, and between presence and absence of word initial /h/. There was substantial individual variability across apraxic speakers for several other phonetic contrasts.