<div dir="ltr">Dear Joseph and Clemens,<div><br></div><div>Use -1 to 2 sec regardless of the fact that your SOA may be (much) shorter than this. It does not matter if the epochs overlap. The reason for this long epoch is because for the later wavelet transform you'll want to use 1.1-sec long sliding window to decompose 3-Hz activity. See my pipeline wiki <a href="http://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Epoch_data_to_-1_to_2_sec">http://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Epoch_data_to_-1_to_2_sec</a></div><div><br></div><div>Makoto</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jun 28, 2016 at 1:20 AM, Clemens DICKHUT <span dir="ltr"><<a href="mailto:clemens.dickhut@uni.lu" target="_blank">clemens.dickhut@uni.lu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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Dear Joseph,
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<div>generally your trial length and your research question/post-processing. If you want to calculate event-related potentials you usually need 1000-500ms pre-stimulus baseline activity to extract the mean amplitude (which is then subtracted from post-stimulus
time points). Depending on the components you want to investigate, i.e. N200/P300, consequentially you will need at least 500ms post-stimulus, better 1000. A good start probably is -500 1000. </div>
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<div>For time-frequency transforms you will need longer epochs, because, depending on the wavelet starting frequency, a substantial amount of time points will be cut away both pre and post stimulus (this is due to the wavelets that take only the middle
time point). I.e. epochs from -1000 3000ms time-frequency transformed with a wavelet starting from 1Hz will leave you with data values from ca. -500 2500. So, be aware of that and go for longer epochs of you want to observe time-frequency activity. Some additional
thing: for time-frequency analyses you may (this is a later step in the analysis) indicate the baseline (if) to be subtracted from -800 to -200 or something like that, to avoid subtracting post-stimulus activity “smearing” into the baseline (due to the reason
mentioned above, especially relevant for low frequencies). </div>
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<div>For both approaches, if you have non-random stimulus overlap or responses leaking into the pre-stimulus period, its sometimes better to go for shorter pre-stimulus times.</div>
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<div>Hope this helps.</div>
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<div>Best, </div>
<div>Clemens</div>
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<div>On 25 Jun 2016, at 22:06, Joseph Nuamah <<a href="mailto:jknuamah@aggies.ncat.edu" target="_blank">jknuamah@aggies.ncat.edu</a>> wrote:</div>
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<div>Dear All,<br>
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I am new to EEGLAB.<br>
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My question is: what determines the choice of epoch length in EEGLAB.<br>
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Thanks.<br>
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Joseph.<br>
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