Automatic processing of taxonomic and thematic relations in semantic priming - Differentiation by early N400 and late frontal negativity.

Most current models of knowledge organization are based on hierarchical (plant-pine) or taxonomic categories (animal-plant). Another important organizational pattern is thematic categories, which performs external or complementary roles in the same scenario or event (bee-honey). The goal of this study was to explore the processing of hierarchical categories and thematic categories under automatic processing conditions that minimize strategic influences. The Evoked response potential (ERP) procedure was used to examine the time course of semantic priming for category members with a short stimulus onset asynchrony (SOA) of 300ms as participants performed a lexical decision task. Six experimental conditions were compared: hierarchical relations (offspring-grandson), internal features (gold-golden), productive relations (bee-honey), script relations (room-tenant), unrelated (star-spoon), and non-word trials (star-derf). We found faster reaction times for related prime-target pairs than unrelated pairs except for productive relations. The ERP data showed that an early N400 effect (200-400ms) was more negative for unrelated words than for all related words. Furthermore, a frontal negativity (400-550ms) elicited by productive relations was smaller (more positive) than other related words. We suggest that the smaller frontal negativity in the processing of productive relations indicates their increased salience in knowledge structure compared to less prominent hierarchical relations. Indeed, the allocation of attentional resources and subsequent recruitment of additional memory processing might be two of the hallmarks of thematic relations.