GSR Signal Contamination w/o GSR

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carsongmr
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Joined: Wed Mar 08, 2017 1:08 am

GSR Signal Contamination w/o GSR

Post by carsongmr » Wed Mar 08, 2017 2:17 am

I am working with an ActiveTwo amp with the GSR upgrade to record 64 + 8ch EEG and have noticed that the 16Hz oscillation from the GSR AUX channels has been bleeding into scalp EEG channels in recent recordings. The level of contamination varies from one channel to the next. No GSR is actually recorded, and there are no electrodes connected to the DIN port (the speed mode is set to 4 and out of convenience all channels are generally recorded even when they are left empty, as the lab regularly uses a wide variety of peripherals).

From existing documentation, I understand that bleeding can be a problem when actually using SC electrodes with drastically different impedences, but in this case there is nothing attached to the port, and the only bridge to EEG channels should be internally. The lab which has been using this amp has used the current setup for some time, with the SC electrodes unplugged, but only recently has interference from these channels been an issue. I am personally unfamiliar with the GSR functionality of the amp and would like to know: a) is it possible to stop the 16Hz oscillator when GSR is not in use? and b) is the interference here due to a misunderstanding of the amp settings (we should just turn off the oscillator), or is it the case that with the SC electrodes unplugged, a properly calibrated amp should not have interference (and we need to send it off to our local rep for repairs)?

Thanks for any information you might be able to share!
Carson G Miller Rigoli

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