In two experiments with event-related potentials (ERPs), we investigated the formation of auditory Gestalts. For this purpose, we used tone sequences of different structure. In the first experiment, we contrasted a rhythmic section to a section with random time values, each embedded in rhythmically irregular context. In the second experiment, melodies were contrasted to randomized sequences. Nonmusicians either had to detect the rhythmic pattern or to memorize short tone excerpts. Random versions in both experiments evoked a significant increase in the amplitude of P1 and P2. Randomized rhythm sections also evoked a late sustained negative potential. The enlarged P1 and P2 for random sequences might reflect stronger integration effort, as the predictability of tone progression was low. Thus, already at the early stage of encoding, sequence processing might be top-down-driven. The late negativity for rhythmically random sections is possibly task-related, reflecting expectancy violation in terms of regularity, since a metrical grid of beats could not be established. The memorizing of tone excerpts did not evoke a late neural correlate. (169)
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