Behaviorism studies observable actions, such as a boy smiling after receiving ice cream or an audience clapping at the end of a performance. Russian physiologist Ivan Pavlov studied how learning behavior is acquired and introduced the principle of classical conditioning. He demonstrated that dogs could learn to associate the sound of a bell with food, salivating in anticipation. John Watson, an American psychologist, also supported the idea that psychology should focus on observable behaviors, like training a pet, and argued this approach could also apply to humans. For instance, a dog praised for sitting is likely to repeat the action, just as a child praised for completing homework is likely to continue submitting it on time. Another American psychologist, B.F. Skinner concentrated on how behavior is affected by its consequences. He introduced the principle of operant conditioning, which states that rewards encourage and punishments discourage actions. For example, rewarding a student with extra playtime for completing homework encourages the repetition of this behavior. Conversely, penalizing neglect by taking away screen time effectively reduces the tendency to avoid homework.