Hi all,<div>thank you a lot for your suggestions. The thing that was not clear to me was the parameter that expresses Raleigh frequency in Fieldtrip. Now it makes much more sense.</div><div><br></div><div>Thanks again, I will try with your suggestions and see what happens</div>
<div><br></div><div>Cheers</div><div><br></div><div>Silvia </div><div><br></div><div><br><br><div class="gmail_quote">On Tue, Jun 26, 2012 at 6:49 PM, Rodrigo Montefusco <span dir="ltr"><<a href="mailto:rmontefusco@med.uchile.cl" target="_blank">rmontefusco@med.uchile.cl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Silvia,<br><br>As I see in your config, you are using 5 cycles per frequency (cfg.t_ftimwin = 5./cfg.foi;), that means that for 2 Hz you need at least 500ms * 5 = 2.5 secs epochs to resolve that frequency. <br>
1.- you can try with longer epochs...(eg 5 secs)<br>
2.- using less cycles per freq.<br><br>please someone correct me if I'm wrong<br><br>cheers<br><br>Y<br><br><div class="gmail_quote"><div><div class="h5">On Tue, Jun 26, 2012 at 12:04 PM, Silvia Pagano <span dir="ltr"><<a href="mailto:silvia.pagano@unitn.it" target="_blank">silvia.pagano@unitn.it</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">Dear list subscribers,<div><br></div><div>I am an ERPer looking for the first time into the world of time-frequency analysis. I am trying to perform some multitaper analysis on a data set. Ideally I would like to perform similar analysis as described in a paper by Gould et al (2011) on Journal of Neurophysiology. (i.e. in their own words "Time-frequency analysis was performed on</div>
<div>all epochs using a multitaper approach (2–30 Hz, 0.5-Hz steps, 500-ms temporal smoothing window, 2-Hz frequency resolution)" )</div><div><br></div><div>I have epochs from -1100 ms to 100 time locked to the stimulus onset and I am trying to replicate the analysis they did. The problem is that I got boundary effects on all my conditions, namely I obtain NaN in the extreme 100 ms of the time window for all frequencies and for very low frequencies (e.g. 2-4Hz) I have no data in the whole time window. I thought I had time windows large enough to avoid boundary effects, however there must be something I am missing in my code. </div>
<div><br></div><div>Here's what I did following the tutorial:</div><div><br></div><div><div><div>cfg = [];</div><div>cfg.output = 'pow';</div><div>cfg.channel = 'EEG';</div><div>cfg.method = 'mtmconvol'; </div>
<div>cfg.foi = 2:2:30;</div><div>cfg.t_ftimwin = 5./cfg.foi; </div><div>cfg.tapsmofrq = 0.4*cfg.foi;</div><div>cfg.toi = -1.1:0.02:0.1;</div><div>cfg.pad = 'maxperlen'; </div><div>TFRmult = ft_freqanalysis(cfg, data); </div>
</div><div><br></div><div><br></div><div>Does anyone have a clue on this?</div><div><br></div><div><br></div><div>Thank you very much</div><span><font color="#888888"><div><br></div><div>Silvia</div>-- <br>
__________________________________<br><br>Silvia Pagano PhD student<br>
CIMeC - Center for Mind/Brain Science<br>Corso Bettini, 31 38068 Rovereto (TN) <br>Tel. <a href="tel:%2B39%200464%20808709" value="+390464808709" target="_blank">+39 0464 808709</a><br><br>
</font></span></div>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>__________________________________<br><br>Silvia Pagano PhD student<br>CIMeC - Center for Mind/Brain Science<br>Corso Bettini, 31 38068 Rovereto (TN) <br>Tel. +39 0464 808709<br>
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