[FieldTrip] excessive channel correlations

[Smulders, F (PSYCHOLOGY)]

I have seen this occasionally, also on Brainvision's BrainAmp. I find it worrying, and would also like a good explanation. I have seen before that open channels on an AD converter just pass a copy of an occupied channel. So if you have a bad connection, that might explain it. 
Subtracting the channel-average would possibly 'hide' a serious hardware problem, it seems to me that you just might end up with pure noise.
kind regards,
Fren


> On 13 Apr 2018, at 08:56, Eelke Spaak <e.spaak at donders.ru.nl> wrote:
> 
> Hi Roy,
> 
> I have no suggestion as to what might be causing this, but one
> suggestion on how to pragmatically deal with it, or at least maybe get
> some more insight.
> 
>> - the problem is there regardless of reference montage (e.g., forehead and
>> averaged mastoids)
> 
> Have you tried common average reference? If the signal is there on all
> channels, subtracting the common average should get rid of it.
> 
> Cheers,
> Eelke
> 
>> - gel bridging, while theoretically possible, seems unlikely given that
>> literally all EEG channels are (almost) identical
>> 
>> We're still investigating but wanted to hear if  anyone ever observed
>> anything like this? Were they able to solve it?
>> 
>> Thanks,
>> 
>> Roy
>> 
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