Inhibition and auditory comprehension in Wernicke's aphasia

Background: While research findings support the presence of inefficiencies in allocation of attention in individuals with aphasia, the cognitive mechanisms behind these inefficiencies remain unclear. One mechanism that would affect resource allocation for selective processing is an impaired inhibitory mechanism which, when normally functioning, would actively suppress distracting information. Aims: The purpose of this study was to investigate the cognitive process of inhibition, at the lexical-semantic level of language processing, and its relation to auditory comprehension in Wernicke's aphasia. Methods & Procedures: The classic Stroop Colour-Word Test was adapted to be applicable for use with an aphasic population. We administered this computerised manual-response, numerical version of the Stroop test to five individuals with Wernicke's aphasia and twelve age- and education-matched non-brain-injured controls. Correlations with Stroop interference examined associations with auditory comprehension as measured by the Token Test and the Complex Ideational Material subtest of the Boston Diagnostic Aphasia Examination. Outcomes & Results: Analysis of the Stroop reaction time and error percentage data indicated that the interference effect was significantly larger for the participants with Wernicke's aphasia than for the controls, without an accompanying increase in facilitation, reflecting an impairment of inhibition in Wernicke's aphasia. In addition, the magnitude of Stroop interference was significantly positively correlated with the clinical-behavioural symptom of severity of auditory comprehension deficits as measured by the Token Test. Conclusions: Findings support an impairment in inhibition at the lexical-semantic level of language processing in Wernicke's aphasia, reflecting the inability to effectively ignore the automatically evoked, distracting stimulus. The significant correlation between the Stroop interference effect and the severity of auditory comprehension deficits suggests that at least part of the attentional difficulties contributing to the striking reductions in auditory comprehension in this population can be attributed to impaired inhibition. Our findings expand upon our understanding of resource allocation in aphasia and reinforce our need to clinically assess and treat reductions in attention for maximised rehabilitation outcome.