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Dear Nina,<div><br></div><div>There is no fieldtrip function in the release allowing for the testing of significant coherence, if I understand correctly what you want. This would be to infer whether a given estimate of coherence is significantly different from zero. This means that you are not testing two conditions against each other (which is what stafun_indepsamplesZcoh is doing; on top of this: it does it for all combinations of channels, and not just for all channels versus a given external reference signal). </div><div>There are two ways in which you can assess the 'significance'. First would be something like a 'shift predictor'. In short, one could shuffle the order of the replications for the reference channel and recompute coherence between the reference and the rest. Provided the reference is not the same signal in each trial, doing this many times would give you an estimate of the 'bias' in coherence. Any observed coherence values in the upper 5% tail then would count as significant (this by the way only works for an external reference channel, and not when you use one of the MEG channels as a reference). </div><div>This shift predictor is perhaps something of an overkill, and you could use a parametric test instead. One way to do this, is to 'Z-transform' the coherence. I am used to using a particular formula which is described in one of our papers (Schoffelen, Science 2005 (supplementary material)); the appropriate references can also be found therein.</div><div><br></div><div>I hope this helps,</div><div><br></div><div>Cheers,</div><div><br></div><div>Jan-Mathijs</div><div><br></div><div><div><div>On May 16, 2009, at 4:05 PM, Nina Kahlbrock wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; 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: 0; "><div class="Section1"><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">Dear Fieldtrip users,<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">I have a question concerning significant coherence. I saw that a similar question was asked before on the mailing list. As I am new to coherence, I did not quite understand the answer.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">So here is my question: I have computed coherence between different MEG sensors and a photodiode. Now, I would like to compute significance levels for these coherence values at different frequencies. Is there a function in fieldtrip that I can use to solve this task? I have found the function ‘statfun_indepsamplesZcoh’. However, I am not sure whether this is the right one to use.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">I would greatly appreciate your help!<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">Thanks in advance.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">Nina<o:p></o:p></span></font></div></div><p>----------------------------------</p><p>The aim of this list is to facilitate the discussion between users of the FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis.</p><p><a href="http://listserv.surfnet.nl/archives/fieldtrip.html">http://listserv.surfnet.nl/archives/fieldtrip.html</a></p><p><a href="http://www.ru.nl/fcdonders/fieldtrip/">http://www.ru.nl/fcdonders/fieldtrip/</a></p></span></blockquote></div><br></div></body></html><p>----------------------------------</p>
<p>The aim of this list is to facilitate the discussion between users of the FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis.</p>
<p> http://listserv.surfnet.nl/archives/fieldtrip.html</p>
<p> http://www.ru.nl/fcdonders/fieldtrip/</p>