<div dir="ltr">Dear FieldTrip users,<div><br></div><div><p class="MsoNormal"><span style="font-family:Arial,sans-serif;background-image:initial;background-repeat:initial">Recently, I am working on the case 1 dataset of epilepsy tutorial. The first patient got the MEG recording from Neuromag and CTF, respectively. I encountered some problems when I tried to depict the Kurtosis topography at<span class=""> channel - </span>level. </span><b></b></p>
<p class="MsoNormal"><b><br></b></p><p class="MsoNormal"><b>Question 1:</b> why and how does the filter affect the kurtosis?</p>
<p class="MsoNormal">Figure 1 and Figure 2 are kurtosis topographies at channel level without band pass filter and with band pass filter, respectively. As we can see, these two figures are very different. Therefore, I am wondering why and how does the frequency filter affect the kurtosis?</p>
<p class="MsoNormal">The figure 1 is generated by the following program;</p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">%% preporcessing the channel level data</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">dataset = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'case1.ds'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg = [];</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.dataset = dataset;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">% cfg.hpfilter = 'yes';</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">% cfg.hpfreq = 10;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">% cfg.lpfilter = 'yes';</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">% cfg.lpfreq = 70;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.channel = {</span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'MEG'</span><span style="font-size:10pt;font-family:"Courier New";color:black">};</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">data = ft_preprocessing(cfg);</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black"> </span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">%% compute channel-level kurtosis</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen"> </span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">datak = [];</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">datak.label = data.label;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">datak.dimord = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'chan'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">datak.kurtosis = kurtosis(data.trial{1}')';</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black"> </span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg = [];</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.comment = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'computed channel-level kurtosis'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">datak = ft_annotate(cfg, datak);</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black"> </span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">%% plot kurtosis topography at channel-level</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:12pt;font-family:"Courier New""> </span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg = [];</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.layout = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'CTF275.lay'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.parameter = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'kurtosis'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black"> </span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">figure;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">ft_topoplotER(cfg, datak);</span><span style="font-size:12pt;font-family:"Courier New""></span></p><p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black"><img src="cid:ii_iquuhkjb0_1560834ba2c4fe95" width="454" height="341"><br><br></span></p>
<p class="MsoNormal" style=""></p>
<p class="" align="center" style="text-align:center">Figure 1 kurtosis topography + no filter + case1.ds</p>
<p class="MsoNormal">If the band pass filter is included in the pre-processing, the kurtosis topography is figure 2; the pre-processing matlab program is</p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:forestgreen">%% preporcessing the channel level data</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">dataset = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'case1.ds'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg = [];</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.dataset = dataset;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.hpfilter = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'yes'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.hpfreq = 10;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.lpfilter = </span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'yes'</span><span style="font-size:10pt;font-family:"Courier New";color:black">;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.lpfreq = 70;</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">cfg.channel = {</span><span style="font-size:10pt;font-family:"Courier New";color:rgb(160,32,240)">'MEG'</span><span style="font-size:10pt;font-family:"Courier New";color:black">};</span><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:10pt;font-family:"Courier New";color:black">data = ft_preprocessing(cfg);</span></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"> <img src="cid:ii_iquui3yi1_15608351d8025965" width="454" height="341"><br></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><span style="font-size:12pt;font-family:"Courier New""></span></p>
<p class="" align="center" style="text-align:center">Figure 2 kurtosis topography + [10Hz 70Hz] filter + case1.ds</p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><b>Question 2:</b> Why the kurtosis topographies at channel level from two dataset case1.ds (figure 1 (no filter), figure 2 (filtered)) and case1_cHPI_raw_trans_sss.fif (figure 3 (no filter) and figure 4 (filtered)) are not consistent? Because these two datasets are measured from the same patient, the kurtosis topography should be consistent. Do you have any idea about this?</p><p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"><img src="cid:ii_iquuilzb2_1560835790c231d7" width="454" height="341"><br><br></p>
<p class="MsoNormal" align="left" style="margin-bottom:0.0001pt"></p>
<p class="" align="center" style="text-align:center">Figure 3 kurtosis topography + no filter + case1_cHPI_raw_trans_sss.fif</p><p class="" align="center" style="text-align:center"><img src="cid:ii_iquuj4ny3_1560835d63a6440a" width="454" height="341"><br><br></p>
<p class="MsoNormal" style=""></p>
<p class="" align="center" style="text-align:center">Figure 4 kurtosis topography + [10Hz 70Hz] filter + case1_cHPI_raw_trans_sss.fif</p><p class="" style="text-align:left">Regards,</p><p class="" style="text-align:left">Rui.</p></div></div>