My version of medialab is 2008.1.20 and the computer i ran it on is a dell PC although we have bootcamp partitioned Macs that I anticipate running the experiment in those too. Maybe this helps. I am hoping you can solve the mystery. Otherwise, if I blacked out the continue, would they be able to proceed with some other key-press, like "enter". I seem to remember this is an option.
Thanks ever so much.
Ljubica