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I'm a EEG hobbyist using Olimex EEG SMT, and I'm using 4 dry, active electrodes to record EEG signals (the Olimex uses bipolar montage, so I actually have 2 channels). However, I cannot measure any waves apart from eye movement and hand/leg movement. I'm thinking of spending more money to improve my EEG setup but I don't know exactly why I'm getting this poor quality recordings.

Why I am not getting better results? Do I need conductive paste or do I need more channels? Would conductive paste improve my results? How much? Would more channels improve the signal together with signal processing?

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Yes and sort of.

Dry electrodes are known for lesser signal quality in comparison to "wet" electrodes. Adding some paste/gel to dry electrodes does help. My professor just got an Emotive Insight and found that this helped quite a bit.

More electrodes does not automatically improve the channel to channel quality. However, more electrodes will allow you to measure activity on different locations more precisely. This may improve your ability to recognize different patterns and, therefore, more processes than blinks and movements. More channels will also improve the quality of Independent Component Analyses (ICA), a tool for recognizing and correcting artifacts.

I cannot tell you how much it will improve though. You can have a look at thesignal-to-noise ratio, but I don't know if you can actually calculate values, or that it only provides a theoretical idea/trend in improvement.

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  • $\begingroup$ When you say "dry" and "wet", you mean "active without gel" and "passive with gel" ? $\endgroup$ – user2540549 Apr 16 '16 at 20:14
  • $\begingroup$ Yes indeed. I had to google the difference between active and passive though. I am also just a beginner namely. $\endgroup$ – Robin Kramer Apr 16 '16 at 20:21
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The number of channels are not the issue at all, its the electrodes that are at fault for your wrong readings. Dry electrodes/ water based electrodes have a much higher impedance when placed on your head. They record relatively good signals but require the user to be absolutely still, any slight movements and muscle/facial movements - even blinks can cause high frequency artifacts and distort your signal horrendously, which might be the reason that you are only viewing Eye blinks in your EEG. Gel based electrodes are the best but extremely irritating to use, the sticky feeling on your head after the experiment is done, is totally the worst.

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