[Eeglablist] Preprocessing steps before Time Frecuency Analysis

[Ruben Perellón Alfonso]

Hello Tarik,

thank you very much for your helpful reply. I would like to elaborate some
more:

We are planing to do coherence analysis, for which ICA and average
reference seem not to be recommended (e.g. Uhlaas 2006 & 2009 for reference
in TF analysis, Thatcher 2010 for reference and ICA in coherence analysis)

The the most important at this point is that I am still unsure about the
re-referencing procedure in EEGLAB. I tried re-referencing to mastoids
(TP9, TP10) directly after data import (after import reference is unknown
in eeglab), and compared with the re-referencing procedure described in
EEGLAB wiki (first get common reference (FCz) back to data, then do average
reference, and finally do mastoids re-referencing), the resulting signals
are quite different, so this two are obviously quite different procedures
in their results. Given that, it would be quite important to be sure that
both procedures are actually correct, namely is direct re-referencing to
mastoids just a wrong thing to do in EEGLAB for data recorded with common
reference?
If to do first average reference is a requirement to do mastoids
re-referencing in EEGLAB, then average reference should be done without
considering the bad channels, as you say, this would mean one should first
reject the bad channels before average reference, and only after,
interpolate them, right?

Best,
Ruben

2016-07-22 6:10 GMT+02:00 Tarik S Bel-Bahar <tarikbelbahar at gmail.com>:

> 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
>>
>> _______________________________________________
>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>> To unsubscribe, send an empty email to
>> eeglablist-unsubscribe at sccn.ucsd.edu
>> For digest mode, send an email with the subject "set digest mime" to
>> eeglablist-request at sccn.ucsd.edu
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20160722/697efa1b/attachment.html>