Possibility for Recognition of Psychic Brain Activity with Continuous Wavelet Analysis of EEG

The brain is a unique organization in nature, possessing the ability for psychic activity, which manifests itself in thoughts, feelings and emotions. In present days, numbers of mathematical methods for analysis of electroencephalogram (EEG) were developed with continuous wavelet transform being one of the most successive approaches for studying of brain activity. This paper is aimed to develop methods for investigation of psychic brain activity with help of continuous wavelet analysis of EEG. Ability of human to realize semantic content of the image presented on the screen was tested. Experiment was accompanied with simultaneous EEG recording, which was held with developed software and PC-based experimental setup. The information capabilities of continuous wavelet transform-based method for EEG analysis were improved for the recognition of specific patterns in human brain activity. Comparative wavelet analysis was carried out for EEG recordings at the moment of awareness of the semantic content of the image and for EEG recordings in the absence of conscious (subjective) perception of the semantic content of the image. Significant differences were shown in the alpha rhythm of EEG for the moments of awareness of the semantic content of the image and for the moments of absence of conscious perception. Continuous wavelet analysis of EEG showed that the alpha rhythm is the main EEG rhythm, which can be used to estimate the presence of subjective perception of the visual image. Significant differences were shown in the alpha rhythm of EEG for the moments of awareness of the semantic content of the image and for the moments of absence of conscious perception. Conducted studies allow to conclude that revealing of brain activity related to visual image awareness is possible through analysis of EEG. How to cite this paper: Yumatov, E.A., Hramov, A.E., Grubov, V.V., Glazachev, O.S., Dudnik, E.N. and Karatygin, N.A. (2019) Possibility for Recognition of Psychic Brain Activity with Continuous Wavelet Analysis of EEG. Journal of Behavioral and Brain Science, 9, 67-77. https://doi.org/10.4236/jbbs.2019.93006 Received: January 31, 2019 Accepted: February 26, 2019 Published: March 1, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Abstract
The brain is a unique organization in nature, possessing the ability for psychic activity, which manifests itself in thoughts, feelings and emotions. In present days, numbers of mathematical methods for analysis of electroencephalogram (EEG) were developed with continuous wavelet transform being one of the most successive approaches for studying of brain activity. This paper is aimed to develop methods for investigation of psychic brain activity with help of continuous wavelet analysis of EEG. Ability of human to realize semantic content of the image presented on the screen was tested. Experiment was accompanied with simultaneous EEG recording, which was held with developed software and PC-based experimental setup. The information capabilities of continuous wavelet transform-based method for EEG analysis were improved for the recognition of specific patterns in human brain activity. Comparative wavelet analysis was carried out for EEG recordings at the moment of awareness of the semantic content of the image and for EEG recordings in the absence of conscious (subjective) perception of the semantic content of the image. Significant differences were shown in the alpha rhythm of EEG for the moments of awareness of the semantic content of the image and for the moments of absence of conscious perception. Continuous wavelet analysis of EEG showed that the alpha rhythm is the main EEG rhythm, which can be used to estimate the presence of subjective perception of the visual image. Significant differences were shown in the alpha rhythm of EEG for the moments of awareness of the semantic content of the image and for the moments of absence of conscious perception. Conducted studies allow to conclude that revealing of brain activity related to visual image awareness is possible through analysis of EEG.

Introduction
The brain is a unique organization in the living nature, possessing the ability for psychic activity, which manifests itself in thoughts, feelings, emotions, i.e. in subjective human's perception of himself and surrounding world.
Despite of substantial progress in modern psychophysiology and neurophysiology, the existing methods cannot allow direct registration and investigation of patterns of brain psychic activity [ Continuous wavelet transform's main advantage over the classic spectral analysis method is the capability of time-frequency analysis of complex nonstationary signals such as EEG. At the same time, possibility for detection of psychic brain activity with help of EEG analysis is still questionable.
The main aim of the present research is to develop informational technology and methods for studying psychic brain activity with help of continuous wavelet analysis of EEG signals.
The objectives of the research are: 1) Improvement of informational capabilities of continuous wavelet transform-based method for EEG analysis, designing of specialized wavelet basis for increasing the effectiveness of detection of specific psychic activity patterns in human brain.
2) Testing of temporal visual discriminating ability of human to realize semantic content of the image during short presentation time.
3) Registration of EEG in different areas of brain, including visual cortex, during the testing of individual discriminating ability of human to realize semantic content of image.

Materials and Methods
In the present study experimental test is performed to evaluate the ability of human to realize semantic content of demonstrated image during very short presentation time. Design of the experiment suggests demonstration of series of images to the human subject. Presentation time is shortened with each subsequent image: the first image is presented for the longest time period while presentation time for the last image is close to 0. The main point of the test is to find the threshold point, when human could recognize the previous image, but fails to recognize the next one due to the short presentation time [10] [11] [12]. The study uses PC-based experimental setup along with software for testing and detection of two types of brain activity based on EEG properties. The first type of activity is related to subjective conscious perception of visual image and the second one is related to absence of this perception due to the short-term presentation of image [13].
Experimental setup is based on PC with two displays, which are used simultaneously during the testing. The first display is used by the experimenter and shows information about experimental settings such as number and type of presented images, time of presentation, etc. The software also provides "Experimenter's window" on this display with instruments to adjust mentioned parameters according to desired experimental design. The second display is used for presentation of visual stimuli to the human subject in "Presentation window". This window contains consequently demonstrated images with presentation time reduced on each consequent step.
The task of the subject is to carefully observe the second display with "Presentation window" and to try to realize demonstrated images. At some threshold point the subject sees image shortly but fails to realize and recognize it. After the experiment the subject is asked for how many images he/she recognized and which images he/she didn't recognize due to short presentation. This is used to estimate the threshold point.

Calculations
Continuous wavelet transform (CWT) is used for analysis of obtained EEG data [5] [6]. CWT is known to be effective in time-frequency analysis of nonstationary signals (including EEG) and as basis for development of algorithms for automatic detection of specific EEG patterns [7] [8] [9].
CWT is a convolution of analyzed signal x(t) and set of basic functions , s τ ϕ : where the asterisk denotes the complex conjugation. Each basic function , s τ ϕ from this set is obtained by compression/extension and time shift of one function called mother wavelet as following: where s-time scale responsible for compression or extension of mother wavelet, τ -time shift of wavelet function, 0 ϕ -mother wavelet. Instead of time shift s it is possible to introduce frequency f = 1/s, which is more convenient in terms of time-frequency analysis.
The CWT-based spectral analysis of biological signals including EEG is usually performed with the Morlet wavelet as the mother function [16] since Morlet wavelet provides good resolution both in time and frequency domains: Resulting skeletons can be used for tracking most significant frequency components in the signal and for analyzing their time dynamics. Such technique provides information about appearance/disappearance of certain specific rhythmic components, which can help to investigate shifts in subject's perception.
Since the main aim of the present paper is to distinct two types of brain activity on EEG (conscious perception of visual image and absence of this perception) Wilcoxon signed-rank test is used. Wilcoxon signed-rank test is a non-parametric statistical hypothesis test used to compare two related samples to assess whether their population mean ranks differ [17].

Results
During experimental work EEG signals are recorded for 10 subjects in the age of 18 -45. Each subject observes 10 series of 25 images with subsequently shortened demonstration time. Example of EEG recordings is illustrated on Figure 1. It is known that activity in these frequency ranges and transitions of dominant frequencies from one range to another before, during and after demonstration of image can provide information about human's attention and concentration [18].  From Figure 2(b), Figure 2(c) one can clearly see that alpha rhythm appears and disappears through EEG recording, which is assumed to be connected with human's ability to realize content of observed image [19] [20]. Thus, distribution of wavelet energy averaged over alpha frequency range (see Figure 2(d), Figure   2(e)) can be considered in order to provide more detailed analysis in alpha range. Analysis shows that in the case of images with short demonstration time (~0 ms) decrease and subsequent increase is far less significant. For example, the second EEG fragment (Figure 2(c), Figure 2(e), Figure 2(g)) shows that alpha activity suffers no substantial decrease or increase for images with very short demonstration time.
Thus, all image demonstrations can be divided into two groups: 1) with increase in alpha activity before and after demonstration and considerable decrease during demonstration (case of Figure 2 Figure 2(g)). It is assumed that dynamics of the first type corresponds to cases when the subject is possible to realize semantic content of the image while dynamics of the second type reflects the absence of conscious (subjective) perception.
After each series of image demonstration, the subject is asked to pick the time moment t cr when he/she recognizes the previous image and doesn't recognize the next image. This time moment can serve as a possible milestone that separates the state with ability to subjective perception from the state without this ability.
In each series image demonstrations are divided into two groups (two related samples): before moment t cr (possible state of subjective perception) and after moment t cr (possible state with lost ability for subject perception). For these two groups statistical analysis is carried out with use of Wilcoxon signed-rank test.
In this analysis the intensity of alpha activity during image perception is compared for these two samples. Wilcoxon criterion is calculated and appears to be P << 0.05. This result implies significant difference in intensity of alpha rhythm in the state with conscious perception and the state without it.

Discussion
Having summarized the results of the experiments described above, one can see that the ability of human to recognize the semantic content of visual stimuli can vary during experiment according to demonstration time of stimuli. These differences in perception can be noted by directly asking the subject and by changes in time-frequency structure of corresponding EEG signals.
It is known that alpha rhythm in occipital area can provide information about human's attention and concentration [18]. Acquired results further contribute to understanding of relations between alpha activity and visual perception. The results show that EEG activity in alpha frequency range is connected to psychic activity during recognition of the semantic content of the image.
The most important thing is dynamics in alpha range (i.e. appearance and disappearance of alpha rhythm) before, during and after visual stimulus. Analysis reveals two scenarios of alpha rhythm dynamics: 1) in the state with conscious perception alpha activity is more pronounced before and after visual stimulus and demonstrate significant drop during perception of visual stimulus; 2) in the state without conscious perception dynamics of alpha rhythm is far less pronounced or completely absent.
The first of observed scenarios is commonly known in visual stimuli-based experiments [19] [20], while the second scenario is more interesting. Absence of significant changes in alpha activity may imply that the subject loses its ability for conscious perception. The second scenario mostly appears during perception of stimuli after time moment t cr , i.e. when the subject fails to recognize the images with short demonstration time. This may suggest that the brain doesn't have enough time to process and recognize incoming visual stimulus, which, in its turn, leads to no increase in visual awareness and no drop in alpha activity.
While alpha activity dynamics is far less pronounced in the second scenario, it is not completely absent in most cases. Occasionally dynamics in alpha range can be observed even during image demonstration after moment t cr . It can be assumed that less pronounced but still presented dynamics of alpha rhythms reflects some kind of psychic activity corresponding to human's self-appraisal about inability to recognize the semantic content of the image.

Conclusions
In the paper, new experimental setup is developed for testing human's ability to realize semantic content of the image during various presentation times. Numbers of experiments are held for volunteers with this setup in order to acquire multichannel EEG recordings.
CWT-based approach is used for time-frequency analysis of the obtained EEG signals. Analysis shows that human's ability to subjective perception of image can be judged according to the state and dynamics of alpha activity in EEG signal.
Significant differences are found in dynamics of alpha rhythm for case with conscious perception of image's semantic content and for case without this perception.
Obtained results suppose that it is possible to detect psychic brain activity connected to perception of image.
Future studies can be aimed to more detailed CWT-based analysis of big experimental EEG data in order to find specific components of alpha rhythm, which are characteristic for psychic brain activity.