Re: Modular EEG Differential Channels

Niels Samuels <niels.samuels <at> gmail.com> writes:

> 
> 
> You always have to use (hold it or attach it to the body) the DRL with 
each montage though. The modular eeg is designed that way. 
> On Thu, May 16, 2013 at 2:49 PM, Niels Samuels <niels.samuels <at> 
gmail.com> wrote:Hi Nishant,I think it works this way: The Olimex device is 
a 2 channel device. If you only want to use only one channel then you short 
the + and - of the unused channel to VGND so that the unused channel isn't 
left floating. The device measures the difference between the + and the - 
electrode of a channel. You could hook up one of the electrodes to the 
earlobe (which is considered neutral, no electric activity) as a reference 
electrode and the other to a specific ten20 site to obtain a signal for that 
site. That way you'd have more of a classic referential montage. If you 
connect both + and - to an "active" site then you would have a standard 
differential montage. I believe it's possible two use both channels in 
referential montage with only one reference electrode using a split cable 
that goes to both the - (or +) of each channel. But I think that can only be 
done with passive electrodes (not the active ones from Olimex).  Hope this 
helps,Regards,Niels
> On Thu, May 16, 2013 at 12:56 PM, Nishant <nishant.sth <at> gmail.com> 
wrote:Hi,
> I'm planning to buy the Olimex EEG-SMT, but before that I want to 
understand
> the design better. I'm not a Neuroscience person, and I don't know much
> about EEGs, so bear with me if I've missed something obvious.
> The Channels seem to be differential in that they measure the difference
> between a pair of electrodes. I'm confused about the rationale behind 
this.
> If it's only for noise reduction won't a common reference (for all
> channels,) or something like the DRL itself, be good enough?
> And what do I get if for example one electrode is at Fp1 and another at 
Fp2?
> It's not simply the difference in left and right hemisphere activity 
because
> from what I understand of the problem of source localization, there is a 
lot
> of mixing. Isn't there an analogy about a cocktail party?
> The design doesn't seem optimal for what they call a daisy-chain
> configuration either. A simple shorting option between neighboring 
electrode
> sockets would have helped if that was the intent.
> I am not complaining about the design at all, the folks at openEEG have
> clearly put in a lot of hard work. It's just that I'm convinced that there
> is a logic behind this design feature, and I'm not able to understand it.
> The way I'll probably end up using it is by using a common reference for 
the
> -ve sockets of each channel, but that seems to be a waste of electrodes. 
Of
> course I could use a common electrode and split the signal, but that might
> just weaken it too much.
> Any help would be awesome.
> Cheers,
> Nishant
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Okay thanks. I'll read up about what the standard differential montage is 
generally used for then.



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efficiently configure, manage, and operate all of your security controls
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