N400 data often did not fully support any of the available theories (even if ERP authors sometimes were compelled to choose a position), suggesting instead that aspects of each were correct. Consider, for example, the N400 work aimed at unearthing why people find concrete words easier to process than abstract words. On a “dual coding” account, concrete materials accrue an advantage by virtue of being represented in two semantic systems – one verbal, in the left hemisphere (LH), which also represents abstract words, and another, image-based, in the RH. By contrast, “context availability theory” grounds concreteness effects in quantitative differences in semantic richness within a common, amodal semantic system. Across a number of studies, N400 results have been systematically mixed: responses to concrete (versus abstract) words manifest different scalp topography, consistent with the dual coding view. However, such differences are reduced for words completing congruent sentences (Holcomb et al 1999), an interaction that is consistent with the context-availability view, albeit not in the precisely predicted form. The N400 data thus call for a theory that combines elements of both accounts.
