This blog post is an excerpt from my conference paper for the 6th International Conference on the Development of Biomedical Engineering - Ho Chi Minh City, Vietnam. I will post a link to my article once it is available. The detection of alpha waves in my data is an important milestone for my project.
This experiment concentrates on the analysis of the alpha rhythms (in the range of 8-12 Hz). Alpha brain waves boost up in EEG signal when subject’s eyes are closed, and when subject’s eyes open, alpha waves’ amplitude reduce. This is an ordinary feature of EEG data processing. From the standpoint of a hardware designer, it’s an important assessment for EEG recording hardware to verify that the system can measure ultra low brainwave signal.
The subject is a student (23-year-old) who participated voluntarily in this experiment. The experiment comprises two phases. First, the subject sits and relaxes on a chair with his eyes open for 15s. There are none stimuli in front of the subject’s eyes. Second, the subject closes his eyes in 5s and opens his eye in 5s for every trial. This protocol is illustrated in Fig 1.
Every run consists at least 5 trials. We conduct 5 runs in the session. EEG data is recorded in two differential channels. Gelled electrodes are placed on the subject’s scalp according to the International Electrode (10-20) Placement System. One Ground (bias) electrode is placed on the left mastoid. The differential pair of channel 1 is placed on the O2 and the right mastoid. The differential pair of channel 2 is placed on the Oz and O1. The sampling rate is 250 Hz. EEG data was high-pass filtered at 0.3Hz to avoid DC drift and a low-pass filter at 43Hz because the signal of interest would be around 8-12Hz. Data is analyzed and visualized using a Matlab Graphical User Interface (GUI). The Power Spectrum Density (PSD) graph of one run is presented in Fig. 2. The result coherences with the hypothesis in which PSD of alpha waves is high (in red color) when subject’s eye is close; PSD of alpha waves is low when subject’s eye is open and relax.
Fig. 1 Protocol for detecting alpha waves
Every run consists at least 5 trials. We conduct 5 runs in the session. EEG data is recorded in two differential channels. Gelled electrodes are placed on the subject’s scalp according to the International Electrode (10-20) Placement System. One Ground (bias) electrode is placed on the left mastoid. The differential pair of channel 1 is placed on the O2 and the right mastoid. The differential pair of channel 2 is placed on the Oz and O1. The sampling rate is 250 Hz. EEG data was high-pass filtered at 0.3Hz to avoid DC drift and a low-pass filter at 43Hz because the signal of interest would be around 8-12Hz. Data is analyzed and visualized using a Matlab Graphical User Interface (GUI). The Power Spectrum Density (PSD) graph of one run is presented in Fig. 2. The result coherences with the hypothesis in which PSD of alpha waves is high (in red color) when subject’s eye is close; PSD of alpha waves is low when subject’s eye is open and relax.
Fig. 2 Spectrogram graph to detect alpha waves
Simulation video
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