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{font-size:10pt;font-family:Tahoma;}</style>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> </body>
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