Auditory evoked potentials and the perception of rhythms.

The amplitudes of the evoked potentials (N1-P2) to successive stimuli usually decrease from the first to the second, and so on. We have studied a special case where the subject hears 4 repetitions of a simple rhythmic pattern (iamb 300-600 ms, or trochee 600-300 ms), the interval between two patterns being 1200 ms. In this case, between the reaction to the last click of a pattern and the first click of the next one, we found an increase of the N1-P2, whereas we might have expected a small decrease for this interval, which has been found by many other authors. This exception accords with the inner experience and the motor reproduction of results. In a succession of rhythmical patterns, where there are no other indices, the interval between two patterns is perceived as a pause or a ground, and is not integrated into the pattern.