Alpha activity decreases during the perception of Necker cube reversals: an application of wavelet transform (original) (raw)
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Biological Cybernetics, 1998
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 signi®cantly 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 coecients obtained in each octave were averaged across trials. The most dominant feature representing the averaged ERP was the delta (0.5±4 Hz) coecient occurring between 250 and 125 ms before the button press. By averaging the subset of the single sweeps containing this property, a sharpening and signi®cant amplitude increase of the response peak was observed.
Anomalous Switching of the Bi-Stable Percept of a Necker Cube: A Preliminary Study
2011
Psychophysiological research has shown anomalous correlations between unconscious states refl ected by physiological fl uctuations and random future conditions. Where the future conditions concerned emotional and neutral events, this anomalous effect has been called presentiment. In the present research, the domain of interest regarding apparent retrocausal effects is further extended to the visual experience of a so-called "transparent" Necker cube. When a picture of this cube is presented to subjects, their experience switches spontaneously between two viewpoints. In one perspective the cube is experienced as observed from "above," in the other it is experienced as observed from "below." We measured switching times from "the above" to "the below" experience. Once the subject had indicated by pressing a button that this shift had taken place, the picture of the transparent cube changed into an opaque presentation of one of the two possible viewpoints. The choice of which perspective was presented, "from above" or "from below", was random. When the opaque view was "from above" this corresponded to the view for which the duration was measured (congruent), the opaque view "from below" was the incongruent condition. Arguing that in the incongruent condition the opaque view would "retrocausally" interfere with the "top view" for which the duration was measured, we predicted that in that condition the duration would be shorter. The switching-time effects found in the pilot and two confi rmatory studies were in the same predicted direction. The pooled results showed a mean difference in switching time of 126 msec. These results seem to fi t into a growing database of anomalous correlations between conscious and unconscious behavior and random future conditions. It extends the domain of these anomalous correlations to other non-emotional events. Alternative possibilities, such as procedural errors, are discussed.
Psychophysical 1-D wavelet analysis and the appearance of visual contrast illusions
IEEE Transactions on Systems, Man, and Cybernetics, 1995
Psychophysical representations built by Gabor visual channels described in complex analytic form are shown to be related to the wavelet transform of visual stimuli under empirically plausible bandwidth constraints. Analysis of the psychophysical wavelet representations of one-dimensional stimuli eliciting some visual contrast illusions (Mach bands and the Craik-Cornsweet-O'Brien illusion) reveals that qualitative aspects of the selective appearance of these illusions
Nonlinear Biomedical Physics, 2009
Background: Compared to the waveform or spectrum analysis of event-related potentials (ERPs), time-frequency representation (TFR) has the advantage of revealing the ERPs time and frequency domain information simultaneously. As the human brain could be modeled as a complicated nonlinear system, it is interesting from the view of psychological knowledge to study the performance of the nonlinear and linear time-frequency representation methods for ERP research. In this study Hilbert-Huang transformation (HHT) and Morlet wavelet transformation (MWT) were performed on mismatch negativity (MMN) of children. Participants were 102 children aged 8-16 years. MMN was elicited in a passive oddball paradigm with duration deviants. The stimuli consisted of an uninterrupted sound including two alternating 100 ms tones (600 and 800 Hz) with infrequent 50 ms or 30 ms 600 Hz deviant tones. In theory larger deviant should elicit larger MMN. This theoretical expectation is used as a criterion to test two TFR methods in this study. For statistical analysis MMN support to absence ratio (SAR) could be utilized to qualify TFR of MMN. Results: Compared to MWT, the TFR of MMN with HHT was much sharper, sparser, and clearer. Statistically, SAR showed significant difference between the MMNs elicited by two deviants with HHT but not with MWT, and the larger deviant elicited MMN with larger SAR. Conclusion: Support to absence ratio of Hilbert-Huang Transformation on mismatch negativity meets the theoretical expectations, i.e., the more deviant stimulus elicits larger MMN. However, Morlet wavelet transformation does not reveal that. Thus, HHT seems more appropriate in analyzing event-related potentials in the time-frequency domain. HHT appears to evaluate ERPs more accurately and provide theoretically valid information of the brain responses.
Detection of P300 Waves in Single Trials by the Wavelet Transform (WT)
Brain and Language, 1999
The P300 response is conventionally obtained by averaging the responses to the task-relevant (target) stimuli of the oddball paradigm. However, it is well known that cognitive ERP components show a high variability due to changes of cognitive state during an experimental session. With simple tasks such changes may not be demonstrable by the conventional method of averaging the sweeps chosen according to task-relevance. Therefore, the present work employed a response-based classification procedure to choose the trials containing the P300 component from the whole set of sweeps of an auditory oddball paradigm. For this purpose, the most significant response property reflecting the P300 wave was identified by using the wavelet transform (WT). The application of a 5 octave quadratic B-spline-WT on single sweeps yielded discrete coefficients in each octave with an appropriate time resolution for each frequency range. The main feature indicating a P300 response was the positivity of the 4th delta (0.5-4 Hz) coefficient (310-430 ms) after stimulus onset. The average of selected single sweeps from the whole set of data according to this criterion yielded more enhanced P300 waves compared with the average of the target responses, and the average of the remaining sweeps showed a significantly smaller positivity in the P300 latency range compared with the average of the nontarget responses. The combination of sweeps classified according to the task-based and response-based criteria differed significantly. This suggests an influence of changes in cognitive state on the presence of the P300 wave which cannot be assessed by task performance alone.
This study uses wavelet decomposition (WLD) to extract mismatch negativity (MMN) from electroencephalogram (EEG) recordings. The proposed method is based on the fact that the frequency responses of WLD conform to the frequency properties of the studied signal. Thus, a suitable wavelet for the decomposition and the appropriate levels for the reconstruction required to extract the desired signal can be selected. The reverse biorthogonal wavelet of the order of 6.8 is suitable for decomposing conventionally averaged EEG recordings of the MMN activity of children elicited by an uninterrupted sound under the oddball paradigm. With seven-level decomposition, the coefficients of the fifth and sixth levels are appropriate for extracting the MMN from the averaged trace. Results show that WLD can be used to extract MMN with much better properties than those of that extracted by the difference wave or an optimal band-pass digital filter. The improved properties mean that the deviant stimuli with larger magnitude deviance in contrast to the standard stimuli can elicit the MMN with a larger peak amplitude and a shorter latency. The proposed method can be used as a preprocessing step for multichannel data processing and for the study of other event-related potentials.
Selection of a Suitable Wavelet for Cognitive Memory Using Electroencephalograph Signal
Engineering
The aim of this study is to recognize the best and suitable wavelet family for analyzing cognitive memory using Electroencephalograph (EEG) signal. The participant was given some visual stimuli during the study phase, which were a sequence of pictures that had to be remembered to acquire the EEG signal. The Neurofax EEG 9200 was used to record the acquisition of cognitive memory at channel Fz. The raw EEG signals were analyzed using Wavelet Transform. A lot of mother wavelets can be used for analyzing the signal, but do not lose any information on the wavelet, some predictions must be made beforehand. The criteria of the EEG signal were narrowed down to the Daubechies, Symlets and Coiflets, and it is the final selection depending on their Mean Square Error (MSE). The best solution would have the least difference between the original and constructed signal. Results indicated that the Daubechies wavelet at a level of decomposition of 4 (db4) was the most suitable wavelet for pre-proce...
Journal of Medical and Biological Engineering, 2012
This study uses wavelet decomposition (WLD) to extract mismatch negativity (MMN) from electroencephalogram (EEG) recordings. The proposed method is based on the fact that the frequency responses of WLD conform to the frequency properties of the studied signal. Thus, a suitable wavelet for the decomposition and the appropriate levels for the reconstruction required to extract the desired signal can be selected. The reverse biorthogonal wavelet of the order of 6.8 is suitable for decomposing conventionally averaged EEG recordings of the MMN activity of children elicited by an uninterrupted sound under the oddball paradigm. With seven-level decomposition, the coefficients of the fifth and sixth levels are appropriate for extracting the MMN from the averaged trace. Results show that WLD can be used to extract MMN with much better properties than those of that extracted by the difference wave or an optimal band-pass digital filter. The improved properties mean that the deviant stimuli with larger magnitude deviance in contrast to the standard stimuli can elicit the MMN with a larger peak amplitude and a shorter latency. The proposed method can be used as a preprocessing step for multichannel data processing and for the study of other event-related potentials.