Authors:

SHTYROV, Y. & PULVERMULLER, F.

Reference:

Year of publication:

2003

CBU number:

5737

Abstract:

To address the cerebral processing of grammar, we used whole-head high-density electro- and magnetoencephalography to record the brain's responses elicited by grammatically correct and incorrect auditory stimuli in the absence of directed attention to the stimulation. Using the two methods, we evaluated mismatch negativity (MMN) earlier proposed as an index of pre-attentive automatic speech processing [1-6]. Two studies were performed: (A) English grammatical and ungrammatical phrases (we come/*we comes) were physically identical up to a divergence point where the grammatical string terminated but the ungrammatical one continued in final -s. In condition 1, the grammatical string was presented as a deviant stimulus against the background of ungrammatical strings and in condition 2, the reverse was used. 64-channel EEG recordings revealed differential responses to the two strings starting already 100-150ms after the divergence point. The ungrammatical deviant elicited an early left-lateralized MMN maximal at fronto-central sites, a short positive deflection thereafter maximal at centro-parietal loci and another fronto-central negativity. Instead, the grammatical string produced a less pronounced MMN with fronto-central distribution. As a control for acoustic/phonetic differences, the responses to "we come" and "*we comes" were compared with those to just "come" and "comes" presented outside of context. Significant Context x Affixation interactions confirmed the conclusion that modulations of the early left-anterior negativity, the sharp positivity, and the late negativity indicate grammatical processing. Minimum-norm current estimates (MCE) of the grammaticality effect revealed a dynamic source in the left frontal cortex. (B) The stimuli were minimal Finnish phrases differing only in one phoneme (also affix), which rendered them as either grammatical or ungrammatical. Acoustic and lexical differences were controlled for by using an orthogonal design in which the phonemeís effect on grammaticality was inverted (mä tuon/*mä tuot vs. *sä tuon/sä tuot). 306-channel MEG demonstrated that occasional syntactically incorrect stimuli elicited larger MMNs (at ~200ms) than correct phrases. Source analysis (single-dipole models and MCE) indicated grammaticality-dependent differential activation of the left superior-temporal cortex suggesting that this brain structure may play an important role in such automatic grammar processing.MMN modulation by grammaticality under non-attend conditions suggests that early syntax processing in the human brain may take place outside the focus of attention. This was found in two unrelated languages with two methods using different stimuli. No P6-like effect was found in either study. We explain larger MMN response to grammatical violations by an unprimed activation of morpheme-related neuronal ensembles, whereas morphemes that match grammatically would be linked through neuronal sequence detectors that provide syntactic priming for correctly placed morphemes [7]. The structures of the left perisylvian cortex appear to play an important role in carrying out such automatic grammar processing.1.Naatanen R et al. Nature 385:432-434 (1997) 2.Pulvermuller F et al. NeuroImage 14:607-616 (2001)3.Shtyrov Y et al. NeuroImage 12:657-663 (2000)4.Korpilahti P et al. Brain Lang, 76:332-339 (2001)5.Shtyrov Y, Pulvermüller F. European J Neurosci 15:1085-1091 (2002)