[Eeglablist] Question Regarding Impedance Problem

[Stephen Politzer-Ahles]

Hi Kathryn,

I think you're right that the EOGs would show the same problem if they use
the same reference as the scalp electrodes, but just because they're
connected to the cap doesn't necessarily mean they do--for some setups the
EOGs are bipolar montages (instead of being referenced to some electrode on
the head, they are referenced to each other). I'm not sure what kind of
setup you have so I'm not sure if that's the case.

Best,
Steve

On Wed, Feb 27, 2013 at 3:28 PM, Kathryn Campbell <
kacey.a.campbell at gmail.com> wrote:

> Thanks for your reply.   I thought that if the ground and reference
> electrodes were not working properly, my eye electrodes would show the same
> problem?  My eye electrodes are connected to the cap. I will attempt to
> measure the impedance for these electrodes separately to see if there is a
> broken connection somewhere.
>
> Thanks
> Kathryn
>
> On 27 February 2013 10:13, Michael Schubert <mschuber at mail.upb.de> wrote:
>
>> Hi Kathryn,
>>
>> from my experience I would suggest to check for broken reference/ground
>> electrode(s). Usually the impedance is measured against a common ground
>> electrode (which you described). To do this, try and see if you can set a
>> different cap-electrode or even an extra-electrode placed somewhere else as
>> ground/reference. If it works and the other electrodes show good impedances
>> again, you probably would have to replace your ground/reference electrode
>> in your cap.
>>
>> Hope this helps,
>>
>> Michael
>>
>>
>> Am 26.02.2013 um 04:25 schrieb Kathryn Campbell <
>> kacey.a.campbell at gmail.com>:
>>
>> Hi,
>>
>> I have a question regarding my impedance's when setting up for an EEG.  I
>> am using an EEG cap and I have had not problems getting my impedances down
>> to an acceptable level until last week.  My facial electrodes (eyes) seem
>> to be fine but my cap electrodes will not reduce impedance at all.  I have
>> tried giving them a clean with ivory wash instead of what I was using
>> previously and this seemed to help a bit- my impedances at least responded
>> when I filled the electrodes with gel.  However, in an effort to reduce my
>> impedances further, I went back to try to improve the ground connection.
>> After doing this, all impedances went back to terrible again and would not
>> respond to gel/abrasion attempts.  Any ideas what is going wrong?
>>
>> Thanks
>> Kathryn
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-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/
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