[Eeglablist] filters, ICA and erp

[Sara Graziadio]

Hello,
Thanks for your suggestion. 

As I was planning to do also a PSD analysis on the data I guess that to remove the mean is not the best method if it works as a non-selective high pass filter, am I right?
 
I am applying the PCA before applying the ICA to reduce the number of components. How the data rank would be modified in this case?
I have to admit that it never happened to me that the muscle artefact is put in a single source with the ICA. Usually it spreads on half of the components, is this only my experience? 

Thanks again

Best wishes

Sara
 

>-----Original Message-----
>From: David Groppe [mailto:david.m.groppe at gmail.com]
>Sent: 05 October 2011 23:10
>To: Sara Graziadio
>Cc: eeglablist at sccn.ucsd.edu
>Subject: Re: [Eeglablist] filters, ICA and erp
>
>Hi Sara,
>   I found that a good way to improve the performance of ICA for ERP
>analysis is to
>1) Epoch your data into one or two second chunks time locked to the
>event of interest
>2) Remove the mean of each epoch at each channel
>3) Run ICA to remove artifacts
>4) Use a standard pre-event time window to baseline your data
>5) Compute your ERPs
>
>Removing the mean of each epoch acts as a crude high-pass filter.
>It's not nearly as selective as a "true" high pass filter but it
>doesn't distort the ERP waveforms as much either.  Moreover we've
>found that the procedure described above massively improves the
>reliability of ICA when compared to standard ERP prestimulus
>baselines:
>
>Groppe, D.M., Makeig, S., & Kutas, M. (2009) Identifying reliable
>independent components via split-half comparisons. NeuroImage, 45
>pp.1199-1211.
>
>Hope this helps,
>       -David
>
>
>
>On Wed, Oct 5, 2011 at 10:46 AM, Sara Graziadio
><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
>>
>>
>>
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>
>
>
>--
>David Groppe, Ph.D.
>Postdoctoral Researcher
>North Shore LIJ Health System
>New Hyde Park, New York
>http://www.cogsci.ucsd.edu/~dgroppe/