View full lesson: http://ed.ted.com/lessons/the-difference-between-classical-and-operant-conditioning-peggy-andover Why is it that humans react to stimuli with certain behaviors? Can behaviors change in response to consequences? Peggy Andover explains how the brain can associate unrelated stimuli and responses, proved by Ivan Pavlov's famous 1890 experiments, and how reinforcement and punishment can result in changed behavior. Lesson by Peggy Andover, animation by Alan Foreman.