[Freesurfer] roisummary question...

Hi, I am running an ROI analysis on a set of event-related data obtained through spmhrf analysis. When I run roisumamry-sess to obtain the values needed to calculate a percent signal change the number of estimations per condition is 1, which makes sense since I am looking at the entire time window. I have three conditions, however, and only three numbers corresponding to each condition to be used in a total % signal change calculation are generated. My question is, how are these overall values for each condition calculated? More specifically, how are the TRs assigned to a particular condition to calculate a value specifc to a condition when each condition overlaps within the timewindow? Thanks in advance to anyone who can help, Cameron