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<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">Dear Fieldtrippers,<span style=""> <br></span></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style=""> </span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">I am a relatively new user of fieldtrip and am very
impressed! </p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">I am interested in comparing differences at certain
frequencies – induced 40-100 Hz – between 2 experimental conditions.<span style=""> </span>My understanding was that I can calculate induced
activity in the gamma range by calculating the power for each trial (subject
average -- freqanalysis) and then averaging across subjects (grand average --
freqdescriptives/freqgrandaverage). </p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">To my dismay, when I plotted the results of my
grandaverage I found a band of power at 55 - 65 Hz for the entire duration of
my epoch. I should add this was not the case when I plotted power across trials
for each participant. <span style=""></span><br></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">Earlier discussions mention computing induced+evoked
(using freqanalysis and freqgrandaverage) and subtracting that from evoked
(using timelockanalysis+freqanalysis) to get extract induced only activity.
However, later posts suggest that this is not a valid approach. </p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">1. Where have I made my mistake? </p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">2. If ((induced+evoked)-evoked)) is not valid, what is
the correct approach to calculating induced activity at 40 - 100 Hz?</p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">Any help would be greatly appreciated! </p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><br></p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">Thank you</p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;">
Bobby Stojanoski</p>
<br clear="all"><br><br>
<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>