<p dir="ltr">Dear Selina,</p>
<p dir="ltr">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.</p>
<p dir="ltr">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.</p>
<div class="gmail_quote">2 gru 2013 21:11 "Lihan Wang" <<a href="mailto:lhwang20@gmail.com">lhwang20@gmail.com</a>> napisał(a):<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal">Dear All,<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"> 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. <u></u><u></u></p>
<p class="MsoNormal"> 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. <u></u><u></u></p>
<p class="MsoNormal"> 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.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Thanks<u></u><u></u></p><p class="MsoNormal">Best regards<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Selina Wang <u></u><u></u></p>
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