Visual mismatch negativity elicited by semantic violations in visual words.

The remarkable rapidity and effortlessness of speech perception and word reading by skilled listeners or readers suggest implicit or automatic mechanisms underlying language processing. In speech perception, the implicit mechanisms are reflected by the auditory mismatch negativity (MMN) response, suggesting that phonemic, lexical, semantic, and syntactic information are automatically and rapidly processed in the absence of focused attention. In visual word reading, implicit orthographic and lexical processing are reflected by visual mismatch negativity (vMMN), the visual counterpart of auditory MMN. The semantic processing of spoken words is reflected by MMN. This study investigated whether semantic processing is also reflected by vMMN. For this purpose, visual Chinese words belonging to different semantic categories (color, taste, and action) were presented to participants in oddball paradigms. A set of words belonging to the same semantic category was frequently presented as standards; a word belonging to a different semantic category was presented sporadically as deviant. Participants were instructed to perform a visual cross-change detection task and ignore the words. Significant vMMN was elicited in Experiments 1 to 3, in which the deviant word carried a semantic radical that overtly indicated the word's semantic category information. The vMMNs were most prominent around 260 ms after word onset, were parieto-occipital distributed, and were significantly left-hemisphere lateralized, suggesting rapid semantic processing of the visual words' category-related information. No significant vMMN was elicited in Experiment 4, in which the deviant word did not carry any semantic radicals. Thus, the semantic radical, which has a high frequency of occurrence because it is carried by many words, may be critical for the elicitation of vMMN.