Thematic Thinking and Cognitive Effort: When Thematic Relations Get Complicated

Semantic memory encodes diverse thematic relations, yet their neurocognitive demands remain poorly understood. To investigate a potential heterogeneity of thematic relations, we recorded ERPs while 41 adults judged the thematic relatedness of thematically related and unrelated noun–noun pairs (e.g., builder – house, apple – seed, cheese – fridge versus baby – coffee). Related targets were recognized faster and elicited reduced N400 and late negativities, confirming a robust thematic priming effect. Critically, processing costs scaled with the proportion of dynamic (change-denoting) events evoked by a noun-noun pair: dynamic thematic relations (e.g., builder – house) produced slower RTs and larger N400/late negativities than static thematic relations (e.g., apple – seed). In contrast, telicity—the presence of an inherent endpoint—did not influence behaviour or ERPs once dynamicity was controlled. Priming effects—and the dynamicity cost—were most pronounced over midline and posterior scalp sites, implicating these regions in event-level semantic integration. These findings reveal fine-grained heterogeneity within thematic knowledge: conceptual change taxes the system of semantic representations and/or semantic control mechanisms, highlighting the importance of dynamicity when modelling event-based relations.