After some playing around, I got it to work. I’m not really sure what I did. I suspect that I may have implemented Erwin’s suggestion incorrectly the first time. In any case, thanks for your help! And to answer your question, I quite like using the engine because once I program the stimuli, my students can take over and easily adapt the parameters of the experiment as they wish. Getting the stimuli in the first place has been the hard part!