Semantic processing in aphasia: evidence from semantic priming and semantic interference

Semantic processing theories propose activation of concepts via semantic features, with interference from semantic neighbours arising due to shared features. Semantic impairment has been explained as damage to activation and interference mechanisms, and linked to impaired semantic control. This study investigated semantic activation and interference in 20 people with aphasia. We found normal semantic priming or hyper-priming, coupled with significant semantic interference effects, in most of the participants, regardless of scores on standard semantic tasks. There was little evidence of a relationship between executive functions and semantic processing. The data indicate that semantic activation is unimpaired in most people with aphasia. Apparent difficulties with semantic processing are predominantly found when tasks involve resolving competition from close semantic neighbours. These novel findings question the use of offline tasks involving semantic competitors in diagnosis of semantic deficits in aphasia - and other conditions such as dementia - and demand revised diagnostic methods.