[Eeglablist] Question regarding ICA

[Stephen Politzer-Ahles]

Hi Davide,

There has been a discussion going on on this list recently about some
similar issues; if you search the archives for recent messages about ICA
and artifacts you should be able to find it. The short answer seems to be
that it's probably best to remove the break. Getting rid of the noise
should give you a better composition for the activity that you're actually
interested in, whereas if you keep the break in there then the components
accounting for the largest proportion of the variance will be from there.
Also, the data discontinuity shouldn't be a problem if you have sufficient
data points (indeed, it's even possible to get a good decomposition out of
epoched data--which of course has lots of discontinuities--if the epochs
are long enough).

Best,
Steve

On Fri, Sep 21, 2012 at 6:29 AM, Davide Baldo <davidebaldo84 at gmail.com>wrote:

> Dear all,
>
> I was wondering about the following problem:
>
> Assume that your experiment has 2 blocks each with 30 Trials (just a
> random numbers). The experiment is divided into 2 blocks in order to give a
> break to the subject at the end of the first block of 30 trials.
> The EEG data during the break will probably be full of any kinds of
> artifacts.
>
> My question is the following: Regarding ICA, what do you do with the EEG
> data recording during the break time? I mean, do you use the complete EEG
> signal to run ICA (including the data recorded during the break time) or do
> you remove the noise data recording during the break?
>
> The point is: if you do not remove that data, then you have a continuous
> signal as input to ICA.
>                    If you do remove that data, you remove a lot of noise,
> but you add a discontinuity in the data you use to run ICA (because you
> must cut the data recorded during the break and join together the remaining
> data)
>
> Thus...is it better to remove that part of the data or not?
>
> Does my question make sense? :)
>
> Thanks in advance for your kind help,
>
>
> Davide.
>
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-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/
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