Hi,

Ive been trying to use FDR on a between-group contrast to increase my sensitivity. In normal FEAT I get strong activations in the insula at the whole brain level, but i have predictions for the OFC and encouragingly at an uncorrected threshold of p=0.001 there is a small but strong blob.

My concern is that when I run the second level copes and varcopes for any between-group contrast the "Probability Threshold is:" reports 0. Given that Feat reports whole brain activity I cant work out why FDR says a probability threshold is 0. When I run the contrasts that are for a single group or for both groups combined there is no problem with the reported probability thresholds and I get thresholded images that look similar, but better than my original Feat analysis.

Is there any chance that FDR doesn't like a between group contrasts? Or is Fsl Feat wrong in telling me that I actually do have between group differences. Also I was wondering whether anyone knew if there was a way to manipulate the cluster extent with FDR or not.

Many thanks,
MaryAnn