Hemispheric contributions to semantic activation: a divided visual field and event-related potential investigation of time-course.

Hemispheric contributions to lexical-semantic processing were investigated using event-related potentials and a divided visual field semantic priming paradigm. Hemispheric activation for pairs related via semantic category membership and association (CA) or via semantic category membership only (CO) was examined over two stimulus onset asynchronies (SOAs). Experiment 1 employed a SOA of 250 ms, and Experiment 2 employed a SOA of 750 ms. Controlled semantic priming was targeted in both experiments via a high relatedness proportion. Behavioral accuracy data revealed significant bilateral priming for both CA and CO conditions at 250 ms SOA. At 750 ms SOA hemispheric differences were observed within the behavioral data, with significant priming of the CO condition and priming for the CA condition approaching significance in the left hemisphere, and significant priming of the CA condition only in the right hemisphere. At 250 ms SOA, ERP analysis revealed bilateral CA activation in the N400 and LPC time windows. The second experiment (750 ms SOA) revealed bilateral CA priming during the N400 time window, with no significant LPC effects. The CO condition did not elicit significant ERP priming within either time window at either SOA. The results indicate no hemispheric differences for the ERP measures, with bilateral hemispheric N400 priming observed for associated category members irrespective of SOA, and a bilateral LPC effect at 250 ms SOA only, under controlled semantic priming conditions.