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Dear Tzvetan,</div>
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thanks you for the quick reply.</div>
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Wouldn't be a problem to use "onepass-zerophase" or "twopass" given that I am interested in phase at stimulus onset?</div>
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Don't both filter-types smear poststimulus activity into the prestimulus interval?<br>
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Best,</div>
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Georgios<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> fieldtrip <fieldtrip-bounces@science.ru.nl> on behalf of Tzvetan Popov <tzvetan.popov@uni-konstanz.de><br>
<b>Sent:</b> Thursday, June 18, 2020 14:27<br>
<b>To:</b> FieldTrip discussion list <fieldtrip@science.ru.nl><br>
<b>Subject:</b> Re: [FieldTrip] single-trial phase at stimulus onset using Hilbert transform</font>
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<div class="" style="word-wrap:break-word; line-break:after-white-space">Dear Georgios,
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<div class="">the reason is your cfg.bpfiltdir = ‘onepass’. This should be zero phase or twopass filter. Yet, you will still get filter artefacts at the edges. I suggest you should re-segment your data, e.g. -1000 to 500ms, filter and then re-segment to -500
to 0 again.</div>
<div class="">Good luck,</div>
<div class="">tzvetan</div>
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<div class="">Am 18.06.2020 um 14:14 schrieb george michael <<a href="mailto:gmichael_@hotmail.com" class="">gmichael_@hotmail.com</a>>:</div>
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Dear Fieldtrip Community,</div>
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I am trying to extract the alpha phase at stimulus onset from single trials.<span class="x_Apple-converted-space"> </span><br class="">
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My approach is to :<br class="">
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1) Band-pass filter the trial segments from -500ms to 0 (<span class="">±</span>1Hz around individual alpha frequency).</div>
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I use the filter 'firws' and filter direction 'onepass' to avoid smearing poststimulus activity into the prestimulus interval.<span class="" style="left:612.92px; top:156.986px; font-size:16.4px; font-family:sans-serif"></span><br class="">
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2) Compute Hilbert transform to extract the instantaneous phase of the bandpass signal.<span class="x_Apple-converted-space"> </span><br class="">
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3) Select the phase at the last sample (t=0) as the one representing phase at stimulus onset.</div>
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<span class=""> cfg=[];<br class="">
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<span class="">cfg.channel = 'O1';<br class="">
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<div class="">cfg.bpfilter='yes';<br class="">
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<div class="">cfg.bpfreq=[foi-1 foi+1];<br class="">
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<div class="">cfg.bpfilttype= 'firws';<br class="">
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<div class="">cfg.bpfiltdir= 'onepass';</div>
<div class="">cfg.hilbert='angle';</div>
<div class="">phase = ft_preprocessing(cfg , trials_prestim);</div>
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<span class=""> for tr=1:length(phase .trial)</span><br class="">
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<div class=""> phase_onset(tr,:)=<span class="">phase<span class="x_Apple-converted-space"> </span></span>.trial{tr}(:,end); % select phase at last sample<br class="">
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<span class=""> end</span></div>
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The problem is that the band-bass signal looks quite weird at the right edge, towards t=0s (see attached figure). </div>
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Do you have any idea what would be the reason for this problem?<span class="x_Apple-converted-space"> </span><br class="">
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And which would be the optimal way to extract phase at stimulus onset?</div>
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Many thanks,<br class="">
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Georgios</div>
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Georgios Michail, MSc.</div>
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Department of Psychiatry and Psychotherapy</div>
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Charite-Universitätsmedizin Berlin<br class="">
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<span id="x_cid:CD0CE12F-5A7D-457E-BDE1-8E2D4C11F836@fritz.box"><bandpass_alpha_singlesubj.png></span><span class="" style="font-family:Helvetica; font-size:12px; font-style:normal; font-variant-caps:normal; font-weight:normal; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; float:none; display:inline!important">_______________________________________________</span><br class="" style="font-family:Helvetica; font-size:12px; font-style:normal; font-variant-caps:normal; font-weight:normal; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none">
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<a href="https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1371%2Fjournal.pcbi.1002202&data=02%7C01%7C%7C75cdf37ebb8c4629c90d08d813830d14%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637280801062055379&sdata=YN7KvEKe8UwFVkTeeQV%2F0B2axKX8LtPgf50ehSehzSA%3D&reserved=0" originalsrc="https://doi.org/10.1371/journal.pcbi.1002202" shash="k1GrvRiDNugECf2VPsKmKJpG3Xq1kZpZQhRST3zqZlYu3f0dHv8zCplgthPcgXucs2LXU8aU0BuDx4nFpDYYCdCOwnZhNZB5Psq8lqNK8mY/vkaBgToApYcFC9C7CM+XJMPMrPRpK84AVeI9iGTB+dSgD0xcp+HYxO2JYXDdbFM=" class="" style="font-family:Helvetica; font-size:12px; font-style:normal; font-variant-caps:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px">https://doi.org/10.1371/journal.pcbi.1002202</a></div>
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