[Marsbar-users] Comparing contrats

[Joseph P. <ph...@ho...>]

Hi,

I am reading the marsbar devel tutorial. At the end of the tutorial, two co=
ntasts are compared (p.30,  "You can see that the contrast value =96 which =
is proportional to the change in signal for a single event =96 is greater f=
or run 3 than for run 1"). My question is: how can I test if those two cont=
rasts are significantly different?

I believe that one answer is to run a single model with run1 and run3 and t=
est the contrast [1 -1] ([Run1 Run3]).=20

However, if the ROI for run1 is different than the ROI for run3, how could =
I compare those two contrasts? In this case, I wouldn't be able to compare =
them inside the same model (suppose I would like to test if left amygadala =
activation is greater than right amygadala activation for a single patient)=
.

A second unrelated question is: For answering the question "does area A on =
average activate more for condition 1 than condition 2", marsbar calculates=
 a new summary time course for each ROI and uses this time course to estima=
te the model. Would it be correct to calculate the mean of the contrast val=
ues for every voxel inside the ROI (calculated in spm con_*.img files) and =
use this value as an estimate of the average activation in the ROI? How thi=
s procedure differs from marsbar method?


Thanks for your help,
Josue
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