The relationship between Penny and Sheldon has always been tenuous, but in one episode Sheldon decides to try his hand at conditioning Penny to behave in certain ways, while he discourages other behaviors of hers. Everyone knows that Sheldon is a genius at theoretical physics, but it turns out that he is fairly proficient with psychology as well.
In “The Gothowitz Deviation,” (season three, episode three) Sheldon rewards Penny with chocolate for what he deems to be “correct behavior.” During this part of the show, Leonard Hofstadter and Penny are dating. Leonard begins to pick up on what Sheldon is doing and calls him out on it.
“Sheldon, you can’t train my girlfriend like a lab rat,” Leonard says.
“Actually, it turns out I can,” Sheldon replies.
Using the concept of operant conditioning – the principles developed by Edward Thorndike and B. F. Skinner - Sheldon uses chocolate to modify Penny’s behavior to be something that he believes is acceptable. But, Leonard argues that it is not right for Sheldon to try to condition Penny’s behavior to his likes.
Sheldon argues that such conditioning will make their lives better, and after all, he is using operant conditioning by following “harmless scientifically valid protocol.” Leonard continues to argue against the practice, and Sheldon asks Leonard if he is forbidding him from conditioning Penny. Leonard rolls his eyes and says that yes, he forbids it.
Sheldon picks up a squirt bottle and sprays Leonard with water saying, “Bad Leonard.”
Watch clips from the episode here.
Sheldon uses positive reinforcement to change Penny’s behavior, which means that he gives Penny something that she likes to encourage the behavior he wants to see. With Leonard, the spray from the water bottle is positive punishment – Sheldon is punishing Leonard by adding something negative to the situation. Of course, it is probably fortunate for Sheldon that Leonard is not the type of guy to get physical – not many people would take a squirt of water to the face like that sitting down.
In the end of the episode, Penny tells Leonard that if he comes over to help her put her bed together, they can spend the night there. He replies that he really does not want to, but then Penny tells him that if they go to her place, they can be as loud as they want in their “amorous activities,” something that Sheldon wants to discourage.
Leonard drops what is in his hands and heads out the door. Sheldon is left standing in the kitchen, where he finishes the episode with the following line: “Sex works better than chocolate to modify behavior. I wonder if anyone else has stumbled onto that…?” Poor Sheldon! Apparently, he has got conditioning down to a science, but aspects of the human psyche will forever elude him.