[Eeglablist] Decimation prior to ICA and related things

[Tarik S Bel-Bahar]

1. not sure if you have to decimate, have seen some people to do this to
better meet requirements for good ICA decompositions.
2. don't think higher sampling rate will give you better ICA. I think it's
more of a matter that ICA is fed data that gives an accurate and lengthy
representation of the whole "Data space".
3. quote from earlier eeglablist post: "the key factor is how much data you
have  (timepoints / channels^2). If this is > 30 (or near to it), then we
find it preferable to return all possible components (since pca does a
rather poor job of separating sources)."
So if below this threshold there is some reason for adding more time to the
protocol, or reducing channels, or  decimation



On Tue, Mar 13, 2012 at 6:00 AM, Modestino, Edward J *HS <
EJM9F at hscmail.mcc.virginia.edu> wrote:

> Dear EEGLAB experts,****
>
> ** **
>
> (1) Is it true that  ICA must be subject, like all the model-based
> spectral analysis methods, to a recommendation that one decimate to the
> lowest frequency capable of representing the actual signal content of the
> data without alienation effects?  *Does one NEED to decimate the data
> before running ICA?*  For instance, we have a data set recorded at 1,000
> Hz.  Do we need to decimate this to approximately 128 or 256?****
>
> ** **
>
> (2 ) According to the formula that Dr. Makeig gave to determine the
> optimal amount of data,  *#timepoints/(#channels)^2*, it would appear
> that a *higher sampling rate will give better ICA results*.  Is this the
> case?****
>
> ** **
>
> (3) Finally, using this formula, *#timepoints/(#channels)^2*, is there a *threshold
> or cutoff* one needs to be exceeded to have the optimal amount of data to
> run ICA. Simply doing the equation without any way to interpret the output
> is not helpful.****
>
> ** **
>
> Thanks for your help,****
>
> Dr. Modestino****
>
> ** **
>
> Edward Justin Modestino, Ph.D.****
>
> Postdoctoral Research Associate****
>
> Ray Westphal Neuroimaging Laboratory****
>
> Division of Perceptual Studies****
>
> Department of Psychiatry and Neurobehavioral Sciences ****
>
> University of Virginia****
>
> Email: ejm9f at virginia.edu****
>
> ** **
>
> ** **
>
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