Semantic interference in the picture-word interference task: Is there a pre-lexical, conceptual contribution to the effect?

Picture naming takes longer in the presence of a semantic-categorically related distractor word compared to an unrelated distractor word. This semantic interference effect in the picture-word interference (PWI) task is an empirical cornerstone in speech production research and of central importance in theory development and evaluation. Prominent models locate the effect at an abstract lexical level, yet only few studies have tested for a possible pre-lexical, conceptual contribution. Moreover, those studies that did are not conclusive. We re-explored the locus of semantic interference by contrasting two task versions that were implemented in as parallel a fashion as possible, but differed with respect to the processing stages involved: naming pictures (requiring conceptual processing and lexical processing) and deciding on their natural size (requiring conceptual processing only). We predicted semantic interference in naming, replicating the standard effect. If part of the effect is localized at the conceptual level, we predicted interference in size decision, too. We found semantic effects in both tasks but with different polarity - interference in naming and facilitation in size decision. This pattern supports the view that semantic interference in PWI has its locus at the lexical level and its origin at the conceptual level.