Classical and operant conditioning are two theories of learning proposed by Ivan Pavlov and B.F. Skinner respectively. Pavlov showed that behaviors can be learned through associating an unconditioned stimulus like food with a neutral stimulus like a bell. Skinner's operant conditioning demonstrated that voluntary behaviors are strengthened through positive reinforcement or weakened through punishment and extinction. Cognitive learning theories proposed by psychologists like Edward Tolman emphasized how mental representations and problem-solving allow for more complex learning than conditioning alone.