$2.$ RESEARCH STUDY: Layne is trying to watch less television. Her friend Ryan is a psychologist who agrees to help her. He creates a treatment plan that involves giving Layne $$5$ for every day that she watches fewer than $90$ minutes of television. He monitors her television watching for three days, treats her for three days and monitors her, and then just monitors her for three more days.

What type of design is Ryan using to change Layne$$s behavior?