Il giorno 26 gen 2021, alle ore 16:18, Douglas N. Greve <dgreve@mgh.harvard.edu> ha scritto:

They way you have specified your contrast is a conjunction of individual 
contrasts, ie, cA>cAc AND cB>cBc. If that what you want? Originally, you 
were just asking about  the interaction

On 1/26/2021 5:17 AM, Paula Maldonado wrote:

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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:

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Dear 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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