Weird ERP results

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Weird ERP results

Post by kessler-lab » Tue Sep 12, 2017 3:37 pm


We bought a new BioSemi system where the CMS/DRL electrodes are part of the 32 electrode set (we have 64 channels thus 2 sets). I used it for the for time now but with our old AD-box. In the previous BioSemi system we had an external electrodes for the CMS/DRL which was plugged into the AD-box.
Because the electrode set were worn out I used the new set but didn't change to the new AD-box.
The ERP results (of all the 19 subjects) look very strange, very noisy base-line and no familiar ERP components (I ran a visual experiment) no N2 or P3 just a general negative amplitude through out the window. Can this be caused by a the old AD-box which had a CMS/DRL plug in but nothing connected to it?
I was told by the eeglab support that the SNR is very bad. I will appreciate any suggestion with how to solve this because I ran several experiments with BioSemi and I have never encountered any problem with the recorded data.

Thank you!

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Re: Weird ERP results

Post by Coen » Wed Sep 13, 2017 5:10 pm

CMS/DRL on set or separate via front panel is exactly the same circuitry. All AD-boxes support CMS/DRL on the A set (without anything connected to the front-panel CMS/DRL).

Is the Common Mode in range (blue light continuously on, offsets between -100 and + 100 mV) ?

What kind of noise? 1 sec pulses (blue light off), mains interference (50/60 Hz) or 1/f (broadband) ? Is the noise Common Mode (same on all channels, decreases 40-60 dB after referencing) ?

Best regards, Coen (BioSemi)

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