Re: Modular EEG Differential Channels

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 <[email protected]> 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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from a single console and one unified framework. Download a free trial.
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