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Thanks for your reply, However I have now a doubt regarding one aspect that I had not noticed before.
What I wanted to do is to perform the contrast (condA>condAcontrol)>(condB>condBcontrol) with the order of my condition being condA, condAcontrol, condB, condBcontrol
You said that to do so I should use -a 1 -c 2 -c 3 -a 4, but I don’t understand why condition 3 is -c and condition 4 is -a. To my understanding a is assigning a positive weight to my predictors, while c is assigning a negative one. So if I run -a 1 -c 2 -c 3 -a 4, am I not testing the contrast (condA>condAcontrol)>(condBcontrol>condB) ?
In addition, if now I want to obtain: (condA>condB)>(condAcontrol>condBcontrol) should I run mkcontrast-sess -analysis analysis -contrast contrastname -a 1 -c 3 -c 2 -a 4, or -a 1 -c 3 -a 2 -c 4?
Thanks,
Paula
Il giorno 27 ott 2020, alle ore 22:50, Douglas N. Greve dgreve@mgh.harvard.edu ha scritto:
You would just run mkcontrast-sess, eg, if your four conditions are ordered condA, condAcontrol, condB, condBcont, then mkcontrast-sess -analysis analysis -contrast contrastname -a 1 -c 2 -c 3 -a 4 If you want it reversed, then just reverse the a's and c's
On 10/23/2020 4:39 AM, Paula Maldonado wrote:
External Email - Use CautionDear experts, I am running an fMRI experiment in which I have four conditions: two main conditions (condition A and condition B) and two respective control conditions (condition Acontrol and condition Bcontrol). I would like to create a map showing significantly greater activity for condition A relative to condition B, after subtracting out the activity for the respective control conditions. In other words, I would like to perform the following contrast: (condition A - condition A control) - (condition B - condition B control) Then I would like to have a map that shows the reverse contrast too:(condition B - condition B control) - (condition A - condition A control).
How do I do that?To obtain the first map: (condition A - condition A control) - (condition B - condition B control) I have tried with the mergecontrasts-sess function with the -conjunction flag and the OR option as detailed below: mergecontrasts-sess -mergedcontrast conjres -conjunction or -analysis analysisname -map sig -space sph -isxavg fixed -contrast Contrast1 2 pos 0 -contrast Contrast 2 pos 0 -s sessionsfMRI/Sub01/bold -hemi lh
where Contrast1= (condition A - condition A control) and Contrast2= (condition B - condition B control) however the map I get is exactly the same as (condition A - condition A control), as if subtracting out Contrast 2 had no impact on the map.
Thanks,
Paula
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