maybe there is something silly I am missing, but I seem to have an issue with using the -ptoz option in fslmaths.

I have run simple Sign Test with randomise and I now want to feed the output to cluster (which wants a zstat). So, I use the --uncorrp option in randomise, then type:

> fslmaths rand_vox_p.nii.gz -ptoz rand_vox_z

Now, opening the rand_vox_z (i.e., the ptoz image) and the rand_tstat1 file (also generated by randomise) in fslview it turns out that for most of the voxels the sign appear flipped between the T and the ptoZ image.

What happened? In fact, how does ptoz even know what sign to assign to a given p-value?

Again, sorry if I'm missing something obvious, but hopefully this will be easy to answer..

 Cheers

R