[Eeglablist] An issue with preprocessing procedure

[Mikołaj Magnuski]

Dear Selina,

I wouldn't worry too much about baseline correction. Many frequency
analysis functions perform some detrending of the data before analysis -
usually just the mean correction (setting mean to zero by subtracting it
from all samples) - for _each_ analysis window (where a single point in
your ERS/ERD corresponds to one analysis window). I'm not sure if this is
the case with the functions/pipeline that you are using, but generally -
baseline correction shouldn't be a problem so you can perform it just as
before.

The only difference between ERP and time-frequency analysis that may be
relevant to you is the choice of a relevant baseline window - namely its
length. For example if you are using 3-cycle wavelets at your lowest
frequency and your lowest frequency of interest is 4 Hz then you need a
baseline of at least 1/4 * 3 = 0.75 seconds long. This is considerably
longer than what is used in many ERP studies, so be sure that your
experimental procedure allows for a meaningful baseline of at least [one
cycle of your lowest frequency of interest in seconds] * [number of wavelet
cycles that you estimate this frequency with]. If your baseline is shorter
than this you may not be able to calculate ERSP for the lowest frequency
correctly.
2 gru 2013 21:11 "Lihan Wang" <lhwang20 at gmail.com> napisał(a):

> Dear All,
>
>
>
>      I’ve been trying to make ERD/ERS calculations of  some preprocessed
> EEG data. However, preprocessing has been strictly implemented according to
> standard ERP preprocessing procedure, which includes baseline correction
> and re-reference.
>
>      After reviewing the literatures applying ERP analysis and ERD/ERS
> analysis separately, I’ve found out that baseline correction and
> re-reference procedures, which are always specified in analysis sections of
> ERP researches,  are rarely referred in the ERD/ERS research.
>
>      I’m wondering whether standard ERP preprocessing procedure is working
> well with EEG analysis? Especially, whether the baseline procedure which
> has changed EEG amplitude of each epoch/trial will have an influence on
> ERD/ERS calculation.
>
>
>
> Thanks
>
> Best regards
>
>
>
> Selina Wang
>
>
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