I have 10 runs in one of my data,in  first 7 runs, I have three tasks conditions  (say A, B and C) and  remaining three runs I have two tasks ( A and B, same task as before). After first level analysis, I have extracted beta parameters using marsbar form a a ROI. However, I noticed that beta values for task A ( and B too)  from run 1:7 are smaller compared to beta for same task A ( and B)  but from run  8 9 and 10th run. So does it because of there are 3 conditions in first 7 runs to model  and 2 conditions in last 3 runs ?  If yes, is there anyway to normalize ... or something to take care of these differences..

Any suggestions would be helpful :)

Thanks

Mark