Debugging and free coffee

A project log for Arduino, EEG, and Free Will

Using an open source platform to investigate the "readiness potential" and what it says about human free will

Patrick Glover 06/21/2016 at 15:471 Comment

Initial results from my first test were... underwhelming. There were a ton of artifacts in the signal. Among these were EOG (electrooculography) and static discharge.

The eye is a dipole, with the cornea being positive and the retina negative. Electric fields caused by movement of this dipole can result in huge artifacts in scalp potential recordings. There are a few ways to control for this. The first option is to manually remove individual trials that are polluted by EOG movement. The second way is to place additional electrodes around the orbital bone and record two channels of EOG movements while also recording EEG on the scalp. Then we would use some algorithm to subtract EOG movement artifacts from the EEG signal afterwards. Alternatively, I could instruct the subjects to fixate their eyes on a certain point. The issue with this method is it requires the subject to put extra attention on maintaining their eye position, which is a bad confounding factor if our experiment has to do with conscious decision making. The best low-tech solution to this issue is... to have subjects close their eyes. It's not perfect, as the eyes tend to slowly drift when the eyelids are closed, but the reduction in movement is good enough for these purposes. Also alpha waves tend to pollute the signal when the subject's eyes are closed, so my solution to that is to offer subjects free coffee. Caffeine is a known suppressor of alpha wave production, and plus it entices people to volunteer to participate in the study.

The issue of static is harder to deal with. Wearing an anti-static cuff only gets you so far. Putting down an anti static mat also helps a bit, but there's still a fair deal of DC drift in the signal. Part of me is convinced EEG has a fairly significant voodoo component to it....


Orlando Hoilett wrote 06/24/2016 at 12:41 point

Awesome stuff! Looks super cool. The Arduino board is relatively noisy. You may find that you can get better results if you make your own custom board. Also USB power is pretty noisy as well which could be problematic. You could try powering your biosensing circuit with a battery, not from the 5 V on the Arduino. Additionally, you could try disconnecting your computer from the power outlet when doing these. Otherwise, carry on my friend!

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