Learning is a process of acquiring knowledge through experience or being taught. There are several types of learning, including classical conditioning, operant conditioning, and observational learning. Classical conditioning involves associating a neutral stimulus with an unconditioned stimulus to elicit a conditioned response, as demonstrated in Pavlov's experiments. Operant conditioning involves voluntary responses that are reinforced or punished to increase or decrease a behavior. Observational learning occurs through observing and imitating others. Factors that influence learning include intelligence, prior knowledge, motivation, and the learning material and methods used. Various therapies also apply learning principles, such as systematic desensitization for phobias.