[Eeglablist] ICA analysis and Interpolation

[Tarik S Bel-Bahar]

Hello Andrea, I think you are re-referencing at a good time.  If you
haven't had a chance to, try Googling the eeglablist + your
keywords/questions to find any similar posts from the past. Makoto's
pipeline mentioned in past eeglablist posts has a
prototypical data processing pipeline. Consider staying in ICA space
and analyzing the components.

You wrote: 1- Is it possible interpolate channel in epoched data or is
it  better to always interpolate in continuous data?
**Yes, I think either way is fine, but it may depend on the algorithm
that is used for interpolation.

You wrote: 2- I have removed bad channels to run ICA, so those
channels are not in the list of channels to be interpolated anymore
after ICA. So, is there a way to interpolate after removing channels?
**Yes, u should be able to use the interpolate function in eeglab gui.
See also the matlab help and Google online documentation on
interpolation function in eeglab.


**Let's say you have 2 infants. One has 45 good channels for ICA, and
one has 40 channels for ICA. No problem. Each one has their own ICA. I
assume you will then "remove the bad ICs" and "rebuild the EEG data"
for each participant. Then you would interpolate channels for each
participant. Then you would have ICA-cleaned data from two
participants, with the same 64 channels for each participant.

**Please note that various groups drop  low channels below the ears
and eyes line before ICA for infant data, e.g., J. Richards)

***I would say take a look at the differences in any in ICA results
when using jsut shorter (~1000 ms) epochs versus using longer (3000
ms+) epochs. They shoud look very similar.






















On Thu, Feb 25, 2016 at 8:39 AM, Andrea Helo <andreahelo at gmail.com> wrote:
> Dear all,
>
> I have an issue regarding ICA for artifact correction that I really would
> appreciate some help with. I would also  appreciate if someone could approve
> or suggest any modifications in my pre-processing order.
>
> Here is some background information:
> I have recorded children data (24-month-olds) with EGI, 128 channels.
> The experiment contains 144 trials (72 per condition) where a picture is
> presented during 500 ms  followed by a word (700 ms) then there is an
> intertrial of 2500 ms (I trigger the trials manually when the child is
> looking at the screen).
> I exported the data, and I am currently starting to pre-process the data
> using EGGLab.
> I have created epochs of 3500 ms in order to run ICA to detect eye-movement
> artifacts (I have chosen 3500ms because I would like to keep as much data as
> possible for ICA. I would like to compare ERP in shorter epochs of 1000 ms
> later).
>
> My pre-processing order is the following:
>
> Filtering (1HZ-30Hz),
> Reducing number of channels to 64 and then removing bad channels
> Re-referencing to average
> Epoching (3500ms),
> Removing baseline,
> Removing bad epochs
> Running ICA to detect artifacts
>
> One thing I am not sure about is whether I am re-referencing- at the right
> point.
>
> Another issue is interpolation. I have read that it is not recomended
> interpolate before running ICA . So I am removing bad channels before
> running ICA but as a consequence I am having different amount of channels
> per subject. I have also read that it is possible interpolate after running
> ICA but I am not sure how to do it and I have two doubts related to that:
>
> 1- Is it possible interpolate channel in epoched data or is it  better to
> always interpolate in continuous data? I have run ICA in epoched data first
> and after that I will have to interpolate in the epoched data.
> 2- I have removed bad channels to run ICA, so those channels are not in the
> list of channels to be interpolated anymore after ICA. So, is there a way to
> interpolate after removing channels?
>
>
> Thanks in advance for your help,
>
> --
> Andrea
>
>
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