Re: Modular EEG Differential Channels

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 <[email protected]>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 <[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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