ANALYSIS OF THE ELECTROENCEPHALOGRAPHIC ACTIVITY DURING THE NECKER CUBE REVERSALS BY MEANS OF THE WAVELET TRANSFORM

In previous studies, a perceptual switching related potential was obta ined during the observation of a multistable dynamic reversal pattern, where the averaging of the single responses was triggered by subjects pressing a button. The present methodological study aims to increase the signal quality of perceptual switching related potentials consider ing the dependence of the measurement method on the reaction time of t he subject, which may vary significantly during a session, leading to low-amplitude waveform in the averaged event-related-potential (ERP). To overcome this problem in measuring the electrophysiological correla te of an internal event, a pattern selection method based on the wavel et transform (WT) is proposed to choose a subset of single ERPs with m ore homogenous latencies. Nine subjects observed a Necker cube and wer e instructed to press the button immediately after perceptual switchin g. A slow, low-amplitude positive wave with frontocentral amplitude ma xima was observed around 250 ms prior to the button press. After the a pplication of a 5 octave WT on single sweeps, the time-frequency coeff icients obtained in each octave were averaged across trials. The most dominant feature representing the averaged ERP was the delta (0.5-4 Hz ) coefficient occurring between 250 and 125 ms before the button press . By averaging the subset of the single sweeps containing this propert y, a sharpening and significant amplitude increase of the response pea k was observed.