Differences in brain potentials to open and closed class words: class and frequency effects

Closed class (determiners, pronouns, conjunctions, prepositions etc.) and o pen class (nouns, verbs, adjectives, adverbs) words have different linguist ic functions and have been proposed to be processed by different neural sys tems. Here, event-related potentials (ERPs) were recorded in young German-s peaking subjects while they read closed class and open class words flashed upon a video-screen. In the first experiment closed class words were sorted into four different frequency categories and open class words into three c ategories. The words were presented in a list with the subjects' task to de tect occasional non-words. A centroparietal negativity (N400) with a peak l atency of about 400 ms varied in amplitude as a function of frequency in bo th classes. The N400 in closed class items, however, was considerably small er than that in open class words of similar frequency. A left anterior nega tivity (N280/LPN) showed some degree of frequency-sensitivity regardless of word class. Only for the very high Frequency closed class words a frontal negativity with an onset of about 400 ms was obtained (N400-700). This N400 -700 effect was replicated in the second study, in which medium frequency c losed and open class words and very high frequency closed class words were presented at the fifth position of simple German sentences. It is suggested that neither N400 nor the left anterior negativity (N280/LPN) distinguish qualitatively between the two word classes and thus claims about different brain systems involved in the processing of open and closed class words are not substantiated electrophysiologically. The N400-700 effect is possibly related to specific grammatical functions of some closed class items, such as determiners. (C) 2000 Elsevier Science Ltd. All rights reserved.