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Benchmark Test Conducted for Neurosky Dry Electrodes Vs Biopack system
NeuroSky has developed a dry sensor system for consumer applications of EEG technology. The NeuroSky system consists of dry electrodes and a specially designed electronic circuit for the dry electrodes. NeuroSky has been conducting benchmark tests of the dry EEG by comparing EEG signals measured by the dry sensor system with signals from the Biopac system, a well known wet electrode EEG system widely used in medical and research applications. EEG was simultaneously recorded by the NeuroSky system and the Biopac system. Electrodes for the two systems were placed at the same location, as close together as possible without interfering with one another. Gold-plated dry electrodes were used for NeuroSky system, while silver-silver-chloride disposable electrodes with gel were used for Biopac system. EEG was recorded for various conditions such as with the subject relaxing and in a meditative state, alert and in an attentive state, and during eye blink artifacts.Following is a comparison of the raw EEG signals of NeuroSky and Biopac systems with the subject in a relaxed state.
The red line represents the raw EEG signal of the Biopac system, while the blue line represents the raw EEG signal of the NeuroSky system. Both systems show a similar wave pattern during the resting state, as well as sensitivity to eye blinks. The raw EEGs of the two systems were then compared more precisely over an interval of 10 seconds. The data analysis interval was arbitrarily chosen from 15 to 25 second in 30-second test data.
To compare the EEG signal characteristics of the two systems, the FFTs of the raw EEG were taken over one second for each system. Then, correlation coefficients for the resulting power density values were computed for frequency bands of one to 30 Hz.
As shown in table, the correlation coefficients of power spectrum between the two EEG signals were high enough. It means that frequency distributions of the two EEG signals are very similar. In the following figures, examples of the raw EEG signal and its FFT for the NeuroSky system and the Biopac system are graphically presented. In the raw EEG graphics, there is a gap of 3 data points per second due to different sampling rate of the two systems (sampling rate of NeuroSky system is 128 Hz and that of Biopac system is 125 Hz.).
Raw EEG signals with dry electrodes of NeuroSky system were compared to those with wet electrodes with Biopac system. FFTs were performed to compare signal characteristics of the EEGs, especially power spectrums. Results show that EEG signals of NeuroSky system are compatible to those of Biopac system.EEGs of Biopac system show a little bit more noise in low frequency bands. It may be caused by longer wires between electrodes and pre-amplifiers. The length of wires were 3 feet in Biopac system, while shorter than 10 inches in NeuroSky system. NeuroSky system also fixes the wires so that they cannot move during EEG measurement. As a result, NeuroSky system is more noise-resistant. NeuroSky system may have an advantage when it is used in real living environment and consumer product applications.
You could download the Original research document here