The effect of semantic similarity on re-learning of vocabulary in activation and inhibition deficit in aphasia.

Semantic similarity between items can cause interference in naming known pictures. Recent studies have shown that this interference extends to the acquisition of new vocabulary in neurotypical adults. However, the influence of such similarity on long-term retention of relearned vocabulary in individuals with aphasia remains unknown. This study examines this issue in two individuals with lexical retrieval deficits, one with difficulty activating lexical items (activation deficit) and the other with difficulty inhibiting lexical competitors (inhibition deficit). Participants were trained for six weeks. Learning was assessed during training, immediately after training, one week after each training session, and finally, two, six and sixteen weeks after the last training session. We found a detrimental effect of semantic similarity on long-term retention in the inhibition deficit, but not in the activation deficit. This dissociation shows that semantic similarity interacts with processes of activation and selection in a manner predicted by theories of incremental learning in language production.