N400 event-related potential indices of induced mood effects on access to category-based world knowledge in central and lateralized visual fields

Comprehending discourse requires integrating information conveyed by the linguistic signal with more general context, including world knowledge and affective information. Across a number of lines of research, right hemisphere processes have been implicated in this integration. Here, in a pair of studies, we examined how mood affects access to category-based world knowledge during language comprehension and probed for hemispheric asymmetries in these effects. In Experiment 1, female participants made category fit judgments for written cues paired with exemplars that were either typical, atypical, or incongruent, for example, “a kind of juice” followed by “grape” (typical), “pear” (atypical), or “nest” (incongruent). Half the trials were presented under a positive mood induction (using photographs from the International Affective Picture System) and half under neutral mood. Replicating published findings, N400 amplitudes, linked to semantic memory access, were graded by category fit, with the most negative responses to incongruent exemplars, the least negative responses to typical exemplars, and intermediate responses to atypical exemplars. Importantly, positively induced mood selectively reduced N400 responses to atypical category exemplars. In Experiment 2, the three types of exemplars were presented lateralized to the right or left visual field. Graded N400 patterns were observed to words in both visual fields, but the facilitative effect of positive mood on semantic processing of atypical exemplars was observed only when initial presentation was directed to the right hemisphere (via the left visual field). Together, these findings show that positive mood enhances access to broader semantic relations via right hemisphere mechanisms, likely through affect-mediated effects on attention.