Differences between noun and verb processing in a minimal phrase context: a semantic priming study using event-related brain potentials.

The aim of the present study was to enforce the priming of either nouns or verbs in order to evoke word-category-specific N400 effects. In two experiments two primes which were either a verb-noun or a noun-noun pair were followed by a semantically related or unrelated target which was a noun or verb, respectively. This target always completed the word sequence to a minimal phrase comprising verb, subject, and object (VNN or NNV triplets). In experiment I subjects judged the semantic relatedness of the target to the two primes, in experiment II subjects first generated an appropriate target of the required word category and then judged the semantic relatedness between self-generated word and target. ERPs were recorded from 124 scalp electrodes. In both experiments verbs and nouns as such evoked reliably distinct ERP topographies between 300 and 800 ms. With verbs in relation to nouns the amplitudes were most often found to be more positive over central to frontal or parietal areas and more negative over occipital and temporo-parietal areas. In contrast, N400 effects proved as topographically invariant for noun and verb targets in both experiments. The results suggest that access to noun and verb representations involves topographically distinct cell assemblies while the N400 effect seems to reflect semantic evaluation and integration processes which are more abstract and independent from a particular word category.