Electropalatographic study of speech sound errors in adults with acquired aphasia

Traditionally speech errors in adults with acquired aphasia have been described as either apraxic errors, characteristic of anterior lesions in the cerebral cortex affecting areas such as Broca's area, or phonemic paraphasic errors due to posterior lesions in areas such as Wernicke’s area. However, studies have reported overlap in the descriptions of apraxic and phonemic paraphasic errors despite the assumption that these errors arise from different levels in the speech planning and execution process. For example, phonemic substitutions are associated with both types of error. Part of the problem is due to difficulties in identifying the precise nature and source of the errors which cannot be resolved by auditory perceptual judgements alone. This study investigates, by means of elcctropalatography (EPG), the location and timing of contact patterns produced by ten adults with acquired aphasia. The subjects were variously diagnosed by traditional classification as Broca’s aphasic with or without apraxia, conduction and anomic. These subjects variously demonstrated atypical patterns when compared to ten control speakers such as: increased temporal and/or spatial variability; specific difficulties in the sequencing and timing of two adjacent lingual consonants; and the presence of intrusive lingual/palatal contact patterns. These errors were usually undetected through auditory analysis. The atypical patterns were not associated uniquely with a particular aphasic syndrome but were subject specific and often related to the site of the lesion within the brain, for example, the basal ganglia. Both subjects diagnosed with apraxia of speech and those with phonemic paraphasia produced the EPG patterns noted above. The EPG data provided insights into the nature and origins of errors such as substitutions which were unavailable from auditory-based analysis. Many of these error patterns could be accounted for by modification to Dell’s model of spreading activation (Dell, 1980, 1985, 1986, 1990). The results have important implications for therapeutic intervention since accurate diagnosis is crucial for effective intervention.