LaVerne goes to a movie theater to watch her favorite movie. About halfway through the movie she becomes aware of an overpowering hunger for popcorn. What she doesn’t realize is that throughout the first part of the movie, a message saying "Eat Popcorn!" was repeatedly flashed on the screen at a speed too fast for her to be consciously aware of it. If her desire for popcorn is due to that message, she is responding to ________.