Automatic processing of grammar in the human brain as revealed by the mismatch negativity

The Mismatch Negativity (MMN), a neurophysiological indicator of cognitive processing, was used to investigate grammatical processes in the absence of focused attention to language. Subjects instructed to watch a silent video film and to ignore speech stimuli heard grammatical and ungrammatical spoken word strings that were physically identical up to a divergence point where they differed between each other by a minimal acoustic event, the presence or the absence of a final -s sound. The sentence we come was presented as a rare deviant stimulus against the background of frequently occurring ungrammatical strings, and, in a different experiment, the ungrammatical string *we comes was the deviant in the reverse design. To control for effects related to differences between the critical words, come and comes, control conditions were used in which the same words were presented out of linguistic context. At 100-150 ms after the divergence point, the ungrammatical deviant stimulus elicited a larger MMN than the correct sentence at left-anterior recording sites. This difference was not seen under the out-of-context conditions. In the time range 100-400 ms after stimulus divergence, a spatiotemporal pattern of grammatically related effects was documented by statistically significant interactions of the word and context variables. Minimum-Norm Current Estimates of the cortical sources of the grammaticality effects revealed a main source in the left frontal cortex. We use a neurobiological model of serial order processing to provide a tentative explanation for the data.