[Eeglablist] Preprocessing steps before Time Frecuency Analysis

[Tarik S Bel-Bahar]

Hello Ruben, some notes below that may be of use. best wishes.


*************************************
Regarding your epoch rejection, order seems generally correct. I would
suggest also visually inspecting and making changes in thresholds if
necessary, and using other sub-tools in the channel-based rejection GUI.
With 128 channels, the data is well suited to ICA based artifact-detection
and ICA-based analyses. If you haven't had a chance to, examine
time-frequency dynamics for particular ICs. See also several tools for
cleaning data that come with eeglab, including "trim outlier" and the
ASR-based continuous data cleaning.

One can drop the mastoid channels after rereference to them.
No need to put back in the Fcz. Consider just dropping bad channels,
average reference with good channels (see e.g, prep pipeline), and then
interpolate bad channels.
However, plenty of researchers "rereference" to all channels at the start
of their pipelines rather than only using good channels.
One could interpolate Fcz as a last step if one wants to report on it.

If you haven't had a chance to, see Makoto's pipeline suggestions, eeglab
online tutorials for time-frequency analysis and all eeglab aspects, as
well google eeglab list for past mentions regarding your topics.



On Sat, Jul 16, 2016 at 2:26 AM, Ruben Perellón Alfonso <
ruben.palfonso at gmail.com> wrote:

> Hello!
>
> I am about to pre-proces data before doing Morlet Wavelet Transform.
> Some trials where already rejected based on visual rejection criteria and
> bad channels where also identified via visual inspection..
> These are the next planned steps:
>
> 1. Re-reference data to linked Mastoids (TP9, TP10)
> 2..Interpolate bad channels.
> 3. Reject epochs based on threshold -+500microV
> 4. Reject epochs based on improbable events, 6SD per channel 2SD for all
> channels.
> 5. Do wavelet transform
>
> I would really appreciate the input regarding how correct the order of
> this steps looks to you, and whether you consider some fundamental step is
> missing.
>
> I also have a concrete question regarding step 1:
> We recorded using a 128 channels Brain Producs system, with a common
> reference at FCz. This reference does not appear on import of data into
> EEGLAB of course. Now I am wondering how to properly re-reference the data.
> In the EEGLAB wiki it says that for linked mastoids, one should first
> create a dummy channel of zeros for the common reference, then do average
> reference keeping the common reference, and only then re-reference again to
> the mastoids. But why can't I just directly re-reference to mastoids? Once
> re-reference is done, is there any reasons why I should keep the reference
> channels in the data?
>
> Thanks
> Ruben
>
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