M. Khodanovich, Y. Bushov, Y. Vyachistaya and A. Ivanov.
Research Institute of Biology and Biophysics, Russian Federation.

The perception and production of short intervals is a fundamental perceptual process that is relatively poorly understood. We hypothesize the process of collation of reproducible rhythm with presented standard sound rhythm will be observed in ERP waveform and this process will not depend on presence of sound accompaniment during the rhythm reproduction. Subjects were presented standard sound rhythm (70 signals, 60 dB, 2000 Hz, 10 ms duration and 2 s interstimulus interval) and after 3-5 s subject was reproduced given rhythm by pressing the right index finger a key. At first series (28 participants) pressing the button was accompanied by tone (60 dB, 2000 Hz, 10 ms). At second series (34 participants) pressing the button wasn't accompanied by tone. Components P50, N85, P170, N225, P290 and slow negative-positive wave with latency of 360-540 ms (PN540) were identified in ERP by Principal Component Analysis. We found decrease of N85 and P170 amplitude, increase of N225 amplitude and negativity of PN540 in ERP on rhythm reproduction with sound accompaniment comparing to rhythm perception. In the absence of sound accompaniment we observe increase of N85, P170 and P290 amplitude, and positivity of PN540 comparing to reproduction with sound accompaniment. The decrease of N85 component we consider as decrease of time uncertainty during rhythm reproduction. Since N225 amplitude increases during rhythm reproduction but it doesn't depend on sound accompaniment, we suppose this component reflects the collation of reproducing intervals with internal time image of presented rhythm stored in working memory. This supposition is confirmed by significant positive correlation of N225 amplitude with accuracy of rhythm reproduction. The differences between series with sound accompaniment and series without it in the interval from 360 to 540 ms are probably explained by differences in mechanisms of cognitive control of rhythm reproduction. The increase of N85, P170 and P290 during rhythm reproduction without sound accompaniment was unexpected. Possibly, it is related to increase of arousal level during performance of task demanding more self-control.

Acknowledgements: The study supported by grants of the Russian Education Ministry and the Russian Foundation of Humanities ? 99-06-00253.