[Eeglablist] LPP and skin potentials

[sahar azarang]

Dear both Stephen and Makoto
Thank you for your helpful responses, I found them so useful.

Sahar Azarang


On Mon, Jan 28, 2013 at 9:58 PM, Stephen Politzer-Ahles <
politzerahless at gmail.com> wrote:

> Hi Sahar,
>
> Like Makoto, I have also sometimes used high-pass filtering to try to get
> rid of skin potentials; if doing so, just be aware of the possible
> consequences of high-pass filters (see Luck, 2005). Some people high-pass
> filter the data for ICA decomposition and then apply those ICA weights to
> the unfiltered data.
>
> As for your concern about deleting data during artifact rejection: of
> course, artifact removal always will remove data, and presumably the ERP
> for every trial includes activation due to the component you are interested
> in, so that data will be removed if that trial is removed during artifact
> rejection. But if that trial is contaminated by artifacts then it has to be
> removed anyway, unless you are confident that you can remove the artifact
> from the trial while preserving the data (e.g., by using ICA or a filter).
> I would not worry about accidentally removing LPPs because they look like
> skin potentials, because in my experience the amplitude of these kinds of
> activity is very different. Artifactual skin potentials have a very large
> amplitude (it will depend on your EEG system and amplifier, but usually
> they are very obvious when I view my raw data at a scale of 60 or 80
> microvolts), whereas components related to cognition are much smaller (in
> my experience such components are not visible to the naked eye without
> averaging across a large number of trials, and even then I have to zoom
> into a scale of 10 or 15 microvolts). I think it's very unlikely that
> you'll "see" an LPP in your raw data and think it's a skin potential.
>
> Hope this helps,
> Steve Politzer-Ahles
>
>
> On Mon, Jan 28, 2013 at 10:52 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>wrote:
>
>> Dear Sahar,
>>
>> To control skin potential you need to control room temperature and
>> moisture. I'm not sure if it is a common practice in recording EEG.
>>
>> Our group uses relatively high cutoff frequency for highpass filter
>> (around 1 Hz) because suppressing the skin potential improves ICA
>> performance.
>>
>> Makoto
>>
>> 2013/1/23 sahar azarang <saharazarang at gmail.com>:
>> > Dear all,
>> >
>> > I have a problem with distinguishing skin potential artefacts and
>> > positive/negative shift in EEG due to brain activity (such as LPP ...),
>> > especially when i'm working with event related potentials. So I don't
>> know
>> > if I am doing correct atefact removing or i am deleting some valuabe
>> data
>> > from eeg data. is there any criterion for this?
>> >
>> > Thanks in advance,
>> > Sahar
>> >
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>>
>>
>> --
>> Makoto Miyakoshi
>> JSPS Postdoctral Fellow for Research Abroad
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
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>
>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/
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