[Eeglablist] filters, ICA and erp

[Alonso Valerdi, Luz M]

Hello Sara,

I've been following your questions and replies and I have undergone the same experience that you are describing. The EMG seems to be mixed with another component, but over the time I started to believe that maybe the EMG doesn't come up over all the trial because the subject didn't move all the time. Are you with me?

On the other hand, I'd like to ask you why you posted previously that the high-pass filter below 0.5Hz is not suitable for ICA processing? Do you have any reference to recommend me about this issue? The point is that I'm filtering my data between 0.1 - 40Hz, but the problem is that certain datasets are stuck during the ICA processing and my computer crashes after several hours. I wonder if it is because of the filtering. Do you have any comment?

I'll really appreciate it!
Cheers
Luz

-----Original Message-----
From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Sara Graziadio
Sent: 06 October 2011 10:51
To: 'David Groppe'; 'japalmer29 at gmail.com'
Cc: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] filters, ICA and erp

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/

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