Articulatory-based Phonemic Paraphasia in Conduction Aphasia: A Dysfunction in Phoneme-to-Articulation Conversion Uncovered Through Crossed Aphasia.

Phonemic paraphasia, a common characteristic of conduction aphasia, has traditionally been attributed to phonological representation dysfunction. An alternative hypothesis posits that phonemic paraphasia arises from difficulty converting phonemes into their corresponding articulatory maneuvers. However, detailed case studies supporting this theory have been lacking. In this report, we present the case of a 61-year-old right-handed man with right temporo-parietal infarction who exhibited crossed aphasia characterized by typical conduction aphasia symptoms (eg, relatively fluent speech with intact comprehension, frequent phonemic paraphasia, and pronounced difficulties in oral repetition) in the absence of distorted articulation, syllable segmentation, and prosody impairment. Despite the frequent occurrence of phonemic paraphasia and articulatory challenges, our patient's phonological representations remained relatively intact. His phonemic paraphasia was often self-corrected to produce correct responses, a feature known as conduit d'approche. During the oral repetition of individual mora (ie, the smallest unit of speech in Japanese), we observed that the patient consistently traced the corresponding Hiragana phonetic symbol accurately, despite his difficulties in articulation. We substantiated this phenomenon through objective assessment and posit that it resulted from an unusual separation of language functions in crossed aphasia-specifically, a disconnection between phonological representations in the right temporo-parietal cortex and speech articulation engrams in the left hemisphere. In this case of conduction aphasia, articulatory-based phonemic paraphasia may be viewed as an inability to convert phonemes into the appropriate articulatory maneuvers rather than as phonological representation dysfunction or apraxia of speech.