A functional deficit in the sensorimotor interface component as revealed by oral reading in Thai conduction aphasia

The contemporary view is that a disruption in phonological encoding underlies the speech production deficit in conduction aphasia. We therefore expect to observe a commonality in phonological errors regardless of task – speaking, reading, or writing. A case report is presented of an oral reading task performed by a Thai conduction aphasic with evidence of localized damage in the left temporoparietal zone. He was instructed to read aloud selections from elementary school materials printed in Thai script at his own pace. A phonological analysis of substitution errors revealed that syllable-initial consonants were more vulnerable to disruption than vowels or tones. Tonal errors were seen to be a secondary consequence of a substitution error involving the syllable-initial consonant. His impaired performance is interpreted as evidence in support of a sensorimotor interface system that converts phonological representations derived from visual orthographic input into articulatory motor representations for speech output.

► Phonological analysis of oral reading errors made by a Thai conduction aphasic.
► Breakdown in phonological encoding of syllable-onset consonants vs. rhyme and tone.
► Most tonal errors occurred secondary to substitution of syllable-onset consonant.
► Lesion site implicates sensorimotor interface system in left temporoparietal zone.
► Visual-to-articulatory conversion is driven by position within syllable hierarchy.