<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Frederic,<div><br></div><div>You may want to have a look at:</div><div><br></div><div><br></div><div><a href="http://fieldtrip.fcdonders.nl/faq/why_does_my_tfr_look_strange">http://fieldtrip.fcdonders.nl/faq/why_does_my_tfr_look_strange</a></div><div><br></div><div><br></div><div>Cheers,</div><div><br></div><div>JM</div><div><br></div><div><br><div><div>On Mar 8, 2011, at 5:44 PM, Frederic Roux wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="hmmessage" style="font-size: 10pt; font-family: Tahoma; "><br>Dear fieldtrip users,<br><br>I have encountered a problem when using dpss to calculate spectras for my data<br>and I was wondering if anyone could help me to determine the origin of this problem.<br><br>The figure in the attachement shows the single trial MEG spectrograms for channel 'MLC11'.<br>I have used fieldtrip, custom code and an equivalent function from the chronux toolbox to compute<br>these spectrograms.<br><br>The upper row of the figure shows the PSD and the spectrograms calculated with the different functions<br>for trial n°1.<br><br>The lower row of the figure shows the PSD and the spectrograms calculated with the different functions<br>for trial n°2.<br><br>As you can see, for trial n°2 the results show strange artifacts.<br><br>The parameters I used across all computations are:<br><br>window length = 0.5 Sec<br>time steps = 0.025 Sec<br>spectral smoothing = 10 Hz<br>number of tapers = 2*(.5*10)-1 = 9<br><br>Here is the fieldtrip code I used:<br><br>cfg = [];<br>cfg.method = 'mtmconvol';<br>cfg.output = 'pow';<br>cfg.taper = 'dpss';<br>cfg.foi = [20:100];<br>cfg.t_ftimwin = .5*ones(1,length(cfg.foi));<br>cfg.tapsmofrq = 10*ones(1,length(cfg.foi));<br>cfg.toi = data.time{1}(1):0.025:data.time{1}(end);<br><br>SPECGRAM = freqanalysis(cfg,data);<br><br>Has anyone ever encountered similar artifacts?<br>Does anyone know the origin of such artifacts?<br><br>Any help would as always be greatly appreciated.<br><br>Frederic<br><span><codecheck2.jpg></span>_______________________________________________<br>fieldtrip mailing list<br><a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><br><a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a></div></blockquote></div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Dr. J.M. (Jan-Mathijs) Schoffelen </div><div>Donders Institute for Brain, Cognition and Behaviour, <br>Centre for Cognitive Neuroimaging,<br>Radboud University Nijmegen, The Netherlands</div><div><a href="mailto:J.Schoffelen@donders.ru.nl">J.Schoffelen@donders.ru.nl</a></div><div>Telephone: 0031-24-3614793</div></div></span></div></span> </div><br></div></body></html>