Induced activity

Bobby Stojanoski stojanoski at UTSC.UTORONTO.CA
Thu Mar 25 18:33:14 CET 2010

Dear Fieldtrippers,

I am a relatively new user of fieldtrip and am very impressed!

I am interested in comparing differences at certain frequencies – induced
40-100 Hz – between 2 experimental conditions.  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).

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

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.

1. Where have I made my mistake?

2. If ((induced+evoked)-evoked)) is not valid, what is the correct approach
to calculating induced activity at 40 - 100 Hz?

Any help would be greatly appreciated!

Thank you

Bobby Stojanoski

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. See also and
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