Phonemic simplification in apraxia of speech and aphasia with phonemic paraphasia

There are varied reports about the extent to which people with apraxia of speech (AOS) simplify the phonemic complexity of utterances they attempt to produce and whether the degree to which they do so might inform differential diagnosis relative to aphasia with phonemic paraphasia (APP). Our study purpose was to determine whether either or both diagnostic groups simplify the phonemic content for words they repeat during a typical motor speech evaluation. 195 people with aphasia after stroke were assigned to four diagnostic groups based on quantitative metrics of core speech criteria for AOS and APP. In addition to the target groups, the sample was divided into a borderline group with equivocal feature combinations (BL) and a group with minimal sound production errors (MIN). Monosyllabic, disyllabic, and multisyllabic words were transcribed phonetically and scored for phonemic complexity. The ratio of produced complexity relative to target complexity - the word complexity measure (WCM) ratio - was compared across groups. According to the WCM ratio, participants in all four groups, including the group with minimal speech sound involvement, simplified more productions than they complicated. Those who produced the most speech sound errors also displayed greater phonemic simplification. People with stroke-induced aphasia sometimes produce words that are phonemic complications of targets, but more often they simplify the phonemic output. We conclude that phonemic simplification at the word level has limited value for differentiating clinically between AOS and APP. Future research should consider comparing alternative simplification measures.