Word frequency and multiple repetition as determinants of the modulation of event-related potentials in a semantic classification task.

We recorded event-related potentials while subjects performed a category membership decision task. The stimuli were words of high and low frequency of occurrence in written English, and each was presented four times. The experiment was intended to explore the interaction of word frequency and multiple repetition on the event-related potential, and thence to investigate the possible loci in time of the effects of these variables. First presentations of low and high frequency words evoked event-related potentials which differed in the presence, in the low word frequency waveforms, of a right-hemisphere dominant negativity peaking at 400 ms. This negativity was very similar to the N400 which may be sensitive to the semantic relations among words in a sequence. Initial repetition diminished this midlatency difference, but gave rise to both earlier and later frequency-related differences. Subsequent multiple repetition abolished the early frequency-related repetition effect, but did not affect amplitudes in the region of N400, nor did it abolish a late positivity, present only for repeated low frequency words.