Background: In aphasia, impairments affecting stages after lexical access have been subdivided into three types: 1. impairments specifying a sequence of phonemes after lexical access (the reproduction variety of conduction aphasia, CA); 2. impairments holding on to these representations during articulatory planning (the short-term memory (STM) variety of CA); and 3. Impairments specifying integrated articulatory/motor plans for clusters of phonemes (apraxia of speech, AoS). Models of speech production, however, suggest more articulated possibilities (i.e., different subtypes of articulatory impairments).
Aims: We investigated the impairment in a person with aphasia whose preliminary assessment revealed mixed speech characteristics, combining features typically used to identify CA – phonological errors across tasks and repeated attempts at the target – with features typically used to identify AoS – phonetic errors and word dysfluencies (phoneme elongations and syllabifications). Our preliminary hypothesis was that there was a difficulty transferring information from an (intact) phonological output buffer to articulatory planning. Slow/noisy transfer would predict dysfluencies, errors selecting motor programs, but also repeated attempts (RA) at revising the output in the face of intact feedback and intact original representations. This hypothesis also predicts effects of position and phonological complexity.
Method and Procedure: We tested CS’s word and nonword repetition, word reading, and picture naming. We quantified lexical and non-lexical errors, repeated attempts, phonetic errors, and syllabifications. We assessed effects of word frequency, word length, phoneme position, and syllabic and phonological complexity.
Results: CS made similar errors across tasks, consistent with a post-lexical impairment. His RAs most often built up a correct target from fragments and/or previously incorrect attempts, similar to a conduite d’approche. He also produced more errors in later positions, and more repeated attempts on longer words. However, inconsistent with decay from an output buffer, phonological errors did not increase with word length. Finally, frequency mattered, consistent with easier/faster access to simpler/more practiced motor plans.
Conclusions: CS’s speech characteristics and anatomical lesion are consistent with transfer limitations between phonology and articulatory planning. However, CS has more difficulties in computing articulatory plans than in selecting and retaining phonological representations, as commonly attributed to CA. CS’s case suggests that different varieties of phonological and articulatory disorders need to be distinguished, beyond a strict dichotomy AoS/CA (e.g., involving transfer limitations and difficulties in computing, selecting,, and/or initiating articulatory plans).