<html dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" id="owaParaStyle"></style>
</head>
<body fpstyle="1" ocsi="0">
<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi all,
<div><br>
</div>
<div>I am raking through my script trying to sort out potential faults in my analysis. </div>
<div><u>One issue I have come across is whether ft_timelock analysis should be performed once, or twice when using lcmv method of beamformer. </u></div>
<div><br>
</div>
<div>The tutorial on lcmv beamfomer found here <a href="http://fieldtrip.fcdonders.nl/tutorial/beamformer_lcmv?s[]=covariancewindow" target="_blank" style="font-size: 10pt;">http://fieldtrip.fcdonders.nl/tutorial/beamformer_lcmv?s[]=covariancewindow</a> seems
to indicate that time-locking is only performed once only in the analysis pipeline. </div>
<div><br>
</div>
<div>However, elsewhere on the FT site, I found the following advice:</div>
<div>"<span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;">In order for the beamformer to work, we need the covariance between sensor pairs. This should be the covariance of</span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;"> </span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;">(a
particular latency window) of the</span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;"> </span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;">averaged single trials. This is essentially different
from the average covariance of the single trials.</span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;"> </span><span style="color: rgb(37, 153, 45); font-family: Courier;"><b><font size="2">Therefore, we have to call timelockanalysis
more than once:</font></b> </span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;">the first time we obtain the evoked field, and</span><span style="color: rgb(37, 153, 45); font-family: Courier; font-size: 10px;"> the second time
we obtain the covariance matrix/ces at interesting latency/ies</span><span style="font-size: 10pt;">"</span></div>
<div><span style="font-size: 10pt;"><br>
</span></div>
<div>Which is correct?</div>
<div><br>
</div>
<div>I have been time locking twice: using data sets which were already time-locked using ft_timelockanalysis, and then time locking again, prior to using ft_sourceanalysis........... Wrong?</div>
<div><br>
</div>
<div>The phrase 'sanity check' comes up quite often on this list, and I absolutely understand! As always, any help is very much appreciated!!</div>
<div><br>
</div>
<div>Kaelasha</div>
<div><br>
</div>
<div><br>
</div>
<div><span style="font-family: Courier; font-size: 10px;"><br>
</span></div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
</body>
</html>