upward trend in EEG signals over a long timeframe of > 50s [resolved]
Hello, I'm collecting some sample data from the openBCI Cyton+Daisy UltraCortex Mark IV (16 channels, dry long comb electrodes). I imported openBCI's .txt readings into EEGLAB on MATLAB and did a plot (scroll) graph, at a timeframe of 100s, and found that most of all my readouts showed a gradual, long term overall increase in the voltage levels as the time of the experiment increased. I'm wondering what might be causing this, and if anyone faces this issue @wjcroft?
https://openbci.com/forum/uploads/editor/hm/dbl4dxs6fkho.png
This has also been observed by Sentdex (skip to 20 min 28 seconds). I don't seem to have come across any literature that suggests such macro brain wave increases which can happen so gradually and significantly over a period of ~100s. (Would be happy to learn if anyone has observed such trends and if it's a well-studied phenomena)
Comments
Hi Yunda,
This called "DC offset" and is typically removed with either a highpass filter at say .5 Hz, or a bandpass from .5 Hz to say 45 Hz.
https://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg
William