To help Keyshawn overcome his fear of giving public speeches, his therapist instructs him to relax and then to imagine speaking to a small audience. Once Keyshawn feels relaxed thinking about this, Keyshawn is instructed to give a speech to three people sitting in a room. Then he gives a speech to five people. Then Keshawn gives a speech to twenty people. Then finally, he gives a speech in front of an audience that fills an auditorium.
The therapist is using which technique?