[Eeglablist] filters, ICA and erp

Fri Oct 14 12:48:20 PDT 2011

Alex,
I don't exactly all the details of your experiment, but usually people get
more dipolar looking IC if you preprocess the data with a 1Hz high pass. So,
you could try it with or without and look at the spatial projection vectors
(i.e., mixing matrix column vectors). Will this high pass filtering have a
huge effect on your data? Better to try it out empirically. Personally, I
think having good dipolar ICs is more important, but ERP folks have have
shown that 1 Hz high passing can really distort the peak pattern, etc.
Rey

On Fri, Oct 14, 2011 at 8:40 AM, Aleksandra Vuckovic <
Aleksandra.Vuckovic at glasgow.ac.uk> wrote:

> Hi,
> I think that my email posted yesterday skipped your attention though it was
> closely related to the topic but under different 'subject'.
> I wonder if this all precaution with filters is necessary if one analyse
> ERP during cue based motor imagination task where time to prepare for
> movement is limited to 1s?
> Many thanks,
> Alex
>
> Sent from my iPhone
>
> On 14 Oct 2011, at 15:25, "Rey Ramirez" <rrramir at uw.edu> wrote:
>
> Hi Steve and Sara,
>
> As far as I know there's absolutely no 'technical reason' why my suggestion
> wouldn't work. And actually it does work! Actually, if people have not been
> doing this I'm not sure what kind of results they are getting since the two
> main issues under discussion: 1) that 1 Hz high-pass filtering on ERP data
> can seriously distort the ERP; and 2) that ICA will not work so well for
> data that has not been 1 Hz high-passed filtered, are indeed quite
> uncontroversial. David's suggestion (hi  David!), pretty much does something
> similar but detrending via DC offsetting.
>
> There are of course BSS algorithms that work in the frequency domain (e.g.,
> complex infomax, or better Independent Vector Analysis (IVA)), that could be
> used to study activity at specific frequency bands, including the slow
> oscillation (<1 Hz), but that's an overkill, and for simple ERP analysis
> just running the ICA on the 1 Hz data, and applying the decomposition to the
> 0.1 Hz data is much more practical and it's what I would recommend, that is,
> if you want to bother doing ICA analysis at all.
>
> Rey
>
> On Thu, Oct 13, 2011 at 9:09 AM, Steve Luck < <sjluck at ucdavis.edu>
> sjluck at ucdavis.edu> wrote:
>
>> Hi Sara.  Unless you care about frequencies per se, epoching and
>> baseline-correcting the data won't be a problem.  From a time-domain
>> perspective, this won't change anything.
>>
>> BTW, someone else suggested using the 1-Hz high-pass cutoff, performing
>> ICA, and then applying the component coefficients to the unfiltered data.
>>  That sounds like a great suggestion, although I don't know if there is a
>> technical reason why it wouldn't work.  Does anyone out there know if there
>> would be a problem with this?
>>
>> Steve
>>
>> ps- The email trail on this topic has gotten out of hand, so I deleted
>> everything except the most recent message and your original message.
>>
>> On Oct 13, 2011, at 7:20 AM, Sara Graziadio wrote:
>>
>> Steve,
>> actually I was refering to your book when I was writing that the filter
>> would deforme/reduce the erp. But following David Groppe's suggestion would
>> mean to reduce activity at different frequency all across the spectrum,
>> wihtout exactly knowing which frequencies I am reducing, am I right? If I
>> want to look at the psd as well as at the erps, would this analysis just be
>> correct? I am always concerned about applying data modification that I
>> cannot fully control..if you know what I mean...
>> Thank you very much
>> Best
>>
>> Sara
>>
>>
>> On Wed, Oct 5, 2011 at 10:46 AM, Sara Graziadio
>> < <sara.graziadio at newcastle.ac.uk>sara.graziadio at newcastle.ac.uk> wrote:
>> Hello,
>> I would like just a suggestion about some data cleaning/analysis I am
>> doing. I
>> am doing an ERP analysis and I want to clean my data first with the ICA.
>> In
>> theory, though, I should not use an high-pass cutoff higher than 0.1 Hz to
>> not
>> reduce the erp amplitude. On the other side the ICA does not work well if
>> the
>> high-pass cutoff is lower than 0.5 Hz...what is then the best method to
>> apply?
>> Has anybody tested how robust the ica is with a 0.1Hz filter?
>> I have also another question: I am doing the analysis on 94 electrodes
>> referenced to Fz. I planned to average reference the data but actually
>> there is
>> quite a large spread of noise on all the electrodes with this method
>> (muscular
>> artefacts for example from the temporal electrodes). But actually almost
>> all
>> the papers are using the average reference so I was surprised, am I the
>> only
>> one having this problem of noise? Would not be better just to keep the Fz
>> reference and then perhaps to average the erps for every different
>> cortical
>> area and do the analysis on these averaged erps?
>>
>> Thank you very much
>>
>> Best wishes
>>
>> Sara Graziadio
>> Research Associate
>> Newcastle University
>>
>>
>>      --------------------------------------------------------------------
>> Steven J. Luck, Ph.D.
>> Director, Center for Mind & Brain
>> Professor, Department of Psychology
>> University of California, Davis
>> Room 109
>> 267 Cousteau Place
>> Davis, CA 95618
>> (530) 297-4424
>> E-Mail:  <sjluck at ucdavis.edu>sjluck at ucdavis.edu
>> Web:  <http://mindbrain.ucdavis.edu/people/sjluck>
>> http://mindbrain.ucdavis.edu/people/sjluck
>> Calendar: <http://www.google.com/calendar/embed?src=stevenjluck@gmail.com&ctz=America/Los_Angeles>
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>> --------------------------------------------------------------------
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>
>
> --
> Rey R. Ramírez, Ph.D.
> MEG Brain Imaging Center
> Institute for Learning & Brain Sciences
> Portage Bay Building
> Box 357988
> University of Washington
> Seattle, WA 98195-7988
> e-mail: <rrramir at uw.edu>rrramir at uw.edu
> Tel: (206) 543-6484
> Fax: (206) 221-6472
> Cell: (619) 709-3590
>
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-- 
Rey R. Ramírez, Ph.D.
MEG Brain Imaging Center
Institute for Learning & Brain Sciences
Portage Bay Building
Box 357988
University of Washington
Seattle, WA 98195-7988
e-mail: rrramir at uw.edu
Tel: (206) 543-6484
Fax: (206) 221-6472
Cell: (619) 709-3590
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