Thank you for your response, Gang. I added the -Clustsim option to 3dttest++ and ran the script. It created 3 output files; the brik and head files and a resid.nii file. However, now the terminal is asking me to input 't-test randomsign'. I'm not sure what to enter here, and regardless of what I enter nothing happens. When I try to close the terminal I get a prompt that there is still a process running in the terminal. What should I do at this point? I have the output files, but this prompt is making me think that there is additional step(s) to do and/or that the 3dttest++/Clustsim operation is incomplete.

Jen