Summing it up: semantic activation processes in the two hemispheres as revealed by event-related potentials

The coarse coding hypothesis suggests that semantic activation is broader in the right hemisphere, affording it an advantage over the left hemisphere for the activation of distantly related concepts or multiple meanings of lexically ambiguous words. Behavioral studies investigating coarse coding have yielded mixed results, perhaps in part because such measures sum across multiple processing stages. To more directly tap into the semantic activation processes that are the focus of the coarse coding hypothesis, the current study combined a visual half-field summation-priming paradigm with the measurement of event-related potentials (ERPs). Two primes converged onto a lateralized, unambiguous target (e.g., lion-stripes-tiger) or diverged onto different meanings of a lateralized, ambiguous target (e.g., kidney-piano-organ); in both cases, the primes were related to one another only through the target. In two experiments, participants either made lexical decisions to the targets or made a semantic-relatedness judgment between primes and target. Priming was measured as reductions in the amplitude of the N400, an ERP component that has been specifically linked to meaning activation and that showed semantic-level priming patterns in both of the tasks used in the present study. Counter to the predictions of the coarse coding hypothesis, equivalent N400 summation priming was observed for targets in the two visual fields, in both types of triplets and in both experiments. Thus, the current results fail to support the hypothesis that semantic activation patterns differ in the two hemispheres and point, instead, to other sources for observed asymmetries in verbal processing.