[Eeglablist] filters, ICA and erp

[Steve Luck]

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> 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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Steven J. Luck, Ph.D.
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