Thanks so much Rick! To give more information, the behavior we're looking at is actually aggressive behavior. In the task, the subject chooses the volume level of a white noise blast to "send to other participants". This is on a scale of 1 (no noise) to 5 (max noise) and is our measure of aggression. We're going to look at aggression to mean vs nice peers (in a contrast). Because of this, I'm not sure if the third option is the best choice. However, the 1st or 2nd option seems more reasonable. To move the trials without a modulator to a different regressor class, would this then be a whole separate timing file? If so, I'm guessing I would then treat that event as "noise" and not use it in my contrasts?

Thank you!