Imagination is the production of sensations, feelings and thoughts informing oneself. These experiences can be re-creations of past experiences, such as vivid memories with imagined changes, or completely invented and possibly fantastic scenes. Imagination helps apply knowledge to solve problems and is fundamental to integrating experience and the learning process. As a way of building theory, it is called "disciplined imagination". A way of training imagination is by listening to storytelling (narrative), in which the exactness of the chosen words is how it can "evoke worlds". One view of imagination links it with cognition, seeing imagination as a cognitive process used in mental functioning. It is used in the form of visual imagery by clinicians in psychological treatment. Imaginative thought may become associated with rational thought on the assumption that both activities involve cognitive processes that "underpin thinking about possibilities". The cognate term, "mental imagery" may be used in psychology to denote the process of reviving in the mind recollections of objects formerly given in sense perception. Since this use of the term conflicts with that of ordinary language, some psychologists have preferred to describe this process as "imaging" or "imagery" or to speak of it as "reproductive" as opposed to "productive" or "constructive" imagination. Constructive imagination is further divided into voluntary imagination driven by the lateral prefrontal cortex and involuntary imagination, such as REM sleep dreaming, daydreaming, hallucinations, and spontaneous insight. The voluntary types of imagination include integration of modifiers, and mental rotation. Imagined images, both novel and recalled, are seen with the "mind's eye". Imagination, however, is not considered to be exclusively a cognitive activity because it is also linked to the body and place, particularly in that it also involves setting up relationships with materials and people, precluding the sense that imagination is locked away in the head. Imagination can be expressed through stories and writings such as fairy tales, fantasies, science fiction. Children often use such narratives and pretend play in order to exercise their imaginations. When children develop fantasy they play at two levels: first, they use role playing to act out what they have developed with their imagination, and at the second level they play again with their make-believe situation by acting as if what they have developed is an actual reality.
Psychologists have studied imaginative thought, not only in its exotic form of creativity and artistic expression but also in its mundane form of everyday imagination. Ruth M.J. Byrne proposed that everyday imaginative thoughts about counterfactual alternatives to reality may be based on the same cognitive processes on which rational thoughts are based. Children can create imaginative alternatives to reality from their very early years. Cultural psychology views imagination as a higher mental function involved in a number of everyday activities both at the individual and collective level that enables people to manipulate complex meanings of both linguistic and iconic forms in the process of experiencing. The phenomenology of imagination is discussed in The Imaginary: A Phenomenological Psychology of the Imagination (French: L'Imaginaire: Psychologie phénoménologique de l'imagination), also published under the title The Psychology of the Imagination, a 1940 book by Jean-Paul Sartre, in which he propounds his concept of the imagination and discusses what the existence of imagination shows about the nature of human consciousness. The imagination is also active in our perception of photographic images in order to make them appear real.