Edit: Hmm, I asked this question a couple years ago. And got an answer a couple years ago! Sorry about that.
I want to show participants a movie clip, and have them hit the space bar to stop the movie when they notice an object in the video. I want the reaction time for that, too. Right now, I can't even figure out how to get the movie to stop playing with a key press -- the "Continue" button at the bottom right of the screen is not showing up. Thanks!