For example, say you have two ROIs placed in distinct locations, and you wish to extract parameter estimates from the contrast A-B from each of those ROIs. Marsbar can do this easily, even flippantly, such a saucy and irreverent child it is. After your ROIs have been created, simply specify the SPM design you wish to extract parameter estimates from. In the case of second-level analyses, the SPM.mat files generated by these analyses will contain a number of time points equal to the number of subjects that went into that analysis; where Marsbar comes in is taking all of the parameter estimates for each subject and averages them over the entire ROI, generating a list of averaged parameter values for each subject.
Once this is done, save the results to a .mat file, load the file into memory, and check the output of SPM.marsY.Y (as in, "Why, Black Dynamite? Why?").
More deets can be found in the following tutorial; for a text-based walkthrough, complete with pictures, check out this link. I believe that both of these approaches are valid with both SPM5 and SPM8 distributions; if not, I apologize.
Unlike when Black Dynamite was denied the chance to apologize for the life he took so needlessly.
