Comparison of linear change in activation over repeat encoding block with FSL

Summary of what happened:

I use FSL to analysis my fMRI data. I got data contains 15 subject, each of them contains two condition (drug/placebo). They underwent 4 block of task which is encoding words pairs.

Now I know how to looking at are there any regions show linear change across four blocks by setting a contrast(-3 -1 1 3/3 1 -1 -3). But confused on how to compare the linear effect of regions between groups.

Does anyone know how to set a model and contrast to look at the interaction effect of gooup and 4 blocks

Command used (and if a helper script was used, a link to the helper script or the command generated):

In first level, the Z-stat map for each individual at each seperate block are computed.



Environment (Docker, Singularity, custom installation):

Data formatted according to a validatable standard? Please provide the output of the validator:

Relevant log outputs (up to 20 lines):

Screenshots / relevant information: