Analysis of the electroencephalographic activity during the Necker cube reversals by means of the wavelet transform |
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Authors: | Ümmühan İşoğlu-Alkaç Canan Başar-Eroğlu Ahmet Ademoğlu Tamer Demiralp Michael Miener Michael Stadler |
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Institution: | Electro-Neuro-Physiology Research and Application Center, University of Istanbul, 34390 ?apa Istanbul, Turkey, TR Institute of Psychology and Cognition Research and Center for Cognitive Science, University of Bremen, D-28334 Bremen, Germany, DE Institute of Biomedical Engineering, Bo?azi?i University, Bebek Istanbul, 80815 Turkey, TR
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Abstract: | In previous studies, a perceptual switching related potential was obtained 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 considering the dependence of the measurement
method on the reaction time of the 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 correlate of
an internal event, a pattern selection method based on the wavelet transform (WT) is proposed to choose a subset of single
ERPs with more homogenous latencies. Nine subjects observed a Necker cube and were instructed to press the button immediately
after perceptual switching. A slow, low-amplitude positive wave with frontocentral amplitude maxima was observed around 250 ms
prior to the button press. After the application of a 5 octave WT on single sweeps, the time-frequency coefficients 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 property, a sharpening and significant amplitude increase of the response peak was observed.
Received: 12 September 1997 / Accepted in revised form: 9 July 1998 |
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