a contrast is a simple linear combination - so in your case you are making a contrast placebo + treatment, i1+i2 is correct


From: SPM (Statistical Parametric Mapping) <[log in to unmask]> on behalf of André Schmidt <[log in to unmask]>
Sent: 13 July 2016 13:29:02
To: [log in to unmask]
Subject: [SPM] effect of task over two conditions/treatments
Dear experts

I have a dataset with two measurements per subject (placebo and treatment). Now I would like to show activation for a specific contrast over both conditions (placebo+treatment). I heard it's invalid to include two contrast files from the same subject into the 1-sample t test design - if this is correct, can I use ImCalc to add this two conditions (i1+i2) and feed the resulting files into the 1-sample t test design? Or should I calculate the average (i1+i2/2) in ImCalc?

Many thanks for your help