ABSTRACTThis study was designed to determine whether the N400 component, described by Kutas and Hillyard as an index of semantic expectancy, would he elicited by deviations involving non‐linguistic expectancies. The stimuli within the four experimental conditions included: 1) sentences, 2) geometric patterns of increasing or decreasing size, 3) scale‐notes of increasing or decreasing frequency, and 4) well‐known French melodies. An N400 appeared only following semantic incongruities within sentences. Non‐linguistic deviations were followed by a late positivity whose amplitude varied across conditions. These results are consistent with an interpretation of N400 as an index of the further processing required by linguistic incongruities rather than by violations of arbitrary or over learned rules in general. However, alternative interpretations exist and are di