Cognitive psychologists use theoretical and computer models to explain processing. Theoretical models are abstract, such as the information processing approach. The IPA suggests that information is processed in stages; input, storage and retrieval in the MSM which is based on the way computers function. Computer models are concrete and involve programming a computer to see if they function the same way that the mind does. If they function the same, this is a concrete theory that suggests the mind functions similarly to a computer and is useful in the development of AI.