Hello,
Ive just run an fMRI experiment in which 14 participants completed two runs
of a task on two test days - so they have 2 runs for a placebo day and 2 runs
for a drug day. I have combined these runs in a higher level analysis for each
participant and then at the group level so I have a placebo gfeat and drug
gfeat.
I would now like to investigate some ROIs using FeatQuery, and would like to
get percentage change values for these ROIs. But am very unsure whether to
do this by feeding in each Cope.feat from the drug & placebo gfeats. I have or
whether I should feed in each individual lower level feats. from each run and
average over these? The task was a block design, with 6 different conditions
plus rest periods on for 24 secs.
As I was unsure I ran all of the above analyses to see if averaging over the
otuput from the two lower level Feat Query analyses would give me the same
percentage change value to that from the output from the gfeat Feat Query
analysis. However this doesnt seem to be the case i.e.,
Outputs from FeatQuery's:
- Mean % signal change (stats/cope) when input was Cope.feat from Gfeat
analysis (combination of run1 and run2) = 0.276
- Mean % signal change (stats/cope) when input was Lower level feat Run 1
= 0.386
- Mean % signal change (stats/cope) when input was Lower level feat Run 2
= 0.08794
The average of 0.386 and 0.08794 isnt 0.276 as I had expected it would.
(I have attached an excel file with the values from the FeatQuery analyses)
Am I doing something wrong? Or have I missed something or need to correct
for something? Or is one method more accurate than the other?
Also why is it the case the the % change values for the PE and COPE are the
same when I run FeatQuery on the Cope.feat from the gfeat analysis but the
PE and COPE values differ from each other when I run the FeatQuery on each
of the lower level feats that make up the gfeat???
Any advice or suggestions would be greatly appreciated,
Many many thanks in advance.
Jess Smith
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