Insights into language processing in aphasia from semantic priming and semantic judgement tasks

The nature of semantic impairment in people with aphasia (PWA) provides the background to the current study, which examines whether different methods of semantic assessment can account for such deficits. Cognitive ability, which has previously been linked to language ability in PWA, may impact on test performance and was therefore also examined. The aims of the current study were to compare performance of control participants and PWA on implicit and explicit assessment of semantics, and to relate it to performance on tests of cognition. The impact of semantically similar versus associative relationship types between test stimuli was also considered. Three experimental semantic tasks were developed, including one implicit measure of semantic processing (Semantic Priming) and two explicit measures (Word to Picture Verification and Word to Picture Matching). Test stimuli were matched in terms of key psycholinguistic variables of frequency, imageability and length, and other factors including visual similarity, semantic similarity, and association. Performance of 40 control participants and 20 PWA was investigated within and between participant groups. The relationship between semantic task performance and existing semantic and cognitive assessments was also explored in PWA. An important finding related to a subgroup of PWA who were impaired on the explicit experimental semantic tasks but demonstrated intact semantic processing via the implicit method. Within tasks some differences were found in the effects of semantically related or associated stimuli. No relationships were found between experimental semantic task performance and cognitive task accuracy. The research offers insights into the role of implicit language testing, the impact of stimuli relationship type, and the complex relationship between semantic processing and cognition. The findings underline the need for valid and accurate measures of semantic processing to be in place to enable accurate diagnosis for PWA, in order to direct appropriate intervention choice and facilitate successful rehabilitation.