Native vs. second language discrimination in the modulation of the N400/N400m

The N400 evoked response component, initially proposed as a marker of semantic incongruity, was later demonstrated to be evoked by various potentially meaningful stimuli, such as words or pseudowords. The present study tested whether the N400 elicited by isolated words and pseudowords was modulated by task instructions thus reflecting controlled processing of linguistic information. In two language discrimination tasks, Finnish adults with English as their second language detected either Finnish or English nouns in a list of Finnish and English words and pseudowords. The same set of stimuli, presented in a random order, was used for both tasks. The amplitudes of both the evoked potentials and their magnetic counterparts were task-language dependent. In both tasks, task-language pseudowords elicited more negative evoked potentials (N400 and P600) than non-task-language pseudowords or words. The left temporal source of the evoked magnetic field was activated more strongly by English than Finnish pseudowords in the English task. This source was also activated more strongly by English pseudowords in the English task than in the Finnish task. However, no similar enhancement of the evoked magnetic field by Finnish pseudowords was observed in the Finnish task. This finding suggests that at the level of multimodal temporal cortex around the superior temporal sulcus, the native language is processed more automatically than the second language and that the controlled processing of linguistic information reflected by the N400 potential is accomplished by a broader neural network extending beyond the association temporal areas.