Moreover, N400 effects were found to generalize across input modalities, including spoken words and American Sign Language signs and even language-like nonwords, i.e., pseudowords (reviewed in Kutas & Van Petten 1994). Importantly for functional characterization, N400 effects (albeit with varying amplitude distributions – topographies -- across the scalp) also were routinely seen to line drawings, pictures, and faces when primed (versus not) by single items or sentence contexts. However, N400-like activity was not observed in response to unexpected events in other structured domains such as music, be they the frequency of a note violating a musical scale sequence or a familiar melody; instead, such deviations elicited P3b-like potentials (Besson & Macar 1987). Clearly, the N400 is not a simple signature of the violation of any arbitrary or over-learned pattern. Overall, the early data suggested that the N400 indexed something fundamental about the processing of meaning and hinted that the meaningful/nonmeaningful dimension may be more important than the linguistic/nonlinguistic dimension.
