[Eeglablist] Options for bad reference (mastoid) channels

[Makoto Miyakoshi]

Dear Becky,

I agree with Benedikt.

> Also, is it ok to re-reference to a common average after having completed
the following processing steps: 1) remove DC offset, 2) 0.1 high-pass
filter, 3) epoch the data?

No problem.
If your high-pass filter works correctly it should remove DC offset too. We
recommend much higher freqs for it. Try 1Hz. It is to specify a pass-band
edge, which is equivalent to 0.5Hz at -6dB.

Makoto



2013/9/29 Benedikt Ehinger <behinger at uos.de>

>  Hi Becky,
> We exclude the bad channels before average reference, else you add a small
> amount of the noise back into all channels. Keep in mind that average
> referencing might reduce the rank of your data (compare the discussions on
> the maillinglist for details).
> To your second question: I think all of these steps should not interfere
> with the average referencing.
>
> Best,
>
> Benedikt
>
>
> Am 26.09.2013 14:28, schrieb Becky Prince:
>
> Dear Makoto,
>
>  Thanks for your response!
>
>  I'll be analyzing my data in channel space, so I'll go with average
> referencing as you suggest.
>
>  Can you (or anyone else) please tell me whether to exclude bad channels
> (including both mastoids and any others) before or after applying a common
> average reference to the data?
>
>  Also, is it ok to re-reference to a common average after having
> completed the following processing steps: 1) remove DC offset, 2) 0.1
> high-pass filter, 3) epoch the data?
>
>  Many thanks!
> Becky
>
>
> ____________________________________________
>
> Becky Gilbert (nee Prince)
> PhD Researcher
>
> Room A109
> Department of Psychology
> University of York
> Heslington, York, YO10 5DD, UK
>
>
> On 25 September 2013 18:46, Makoto Miyakoshi <mmiyakoshi at ucsd.edu> wrote:
>
>> Dear Becky,
>>
>>  > I believe the convention is to use the average of linked ears or
>> mastoids as the reference for optimal measurement of these components,
>>
>>  It depends on whether you want to use ICA to analyze your data in the
>> source-resolved EEG or not. If you do, re-reference does not affect the ICA
>> results. If you want to use channel EEG for the final analysis, I recommend
>> average referencing. If you need to choose 1 electrode, choose Cz or FCz
>> because that's another 'convention' I've seen so far (may not specific to
>> your task though). Cz and FCz are easy to interpolate.
>>
>>  Makoto
>>
>> 2013/9/18 Becky Prince <becky.prince at york.ac.uk>
>>
>>>  Dear EEGLAB list,
>>>
>>>  I've run an ERP study on auditory temporal expectations in which I'm
>>> interested in the auditory N2b and P3b components.  I believe the
>>> convention is to use the average of linked ears or mastoids as the
>>> reference for optimal measurement of these components, but my mastoid
>>> channels are consistently noisy in all of my participants.  The mastoid
>>> channels have higher impedances (~15 KOhms) than the other sites, probably
>>> due to the fact that the caps we use have built in mastoid sites that don't
>>> fit close enough to the skin.
>>>
>>>  I'm guessing it's a bad idea to re-reference to noisy channels, so I'm
>>> wondering what my options are.  Can anyone explain what they would do in
>>> this situation?  Are there any resources that explain the effects of
>>> re-referencing on specific components?  I'm wondering if I'll be able to
>>> see changes in N2b/P3b if I use another reference, e.g. average of all
>>> electrodes, and how the appearance of the components (sites/polarities)
>>> will be different from those typically reported with a linked ear or
>>> mastoid reference.
>>>
>>>  Apologies for the fact that this isn't strictly an EEGLAB question -
>>> I'm hoping someone will still offer some advice!
>>>
>>>  Thanks,
>>> Becky
>>>  ____________________________________________
>>>
>>> Becky Gilbert (nee Prince)
>>> PhD Researcher
>>>
>>> Room A109
>>> Department of Psychology
>>> University of York
>>> Heslington, York, YO10 5DD, UK
>>>
>>>  _______________________________________________
>>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>>> To unsubscribe, send an empty email to
>>> eeglablist-unsubscribe at sccn.ucsd.edu
>>> For digest mode, send an email with the subject "set digest mime" to
>>> eeglablist-request at sccn.ucsd.edu
>>>
>>
>>
>>
>>  --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>
>
>
> _______________________________________________
> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
> To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.ucsd.edu
> For digest mode, send an email with the subject "set digest mime" to eeglablist-request at sccn.ucsd.edu
>
>
>
> _______________________________________________
> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
> To unsubscribe, send an empty email to
> eeglablist-unsubscribe at sccn.ucsd.edu
> For digest mode, send an email with the subject "set digest mime" to
> eeglablist-request at sccn.ucsd.edu
>



-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20130930/490ecdbe/attachment.html>