In pyschology, the theory that the conscious and nervous processes vary concomitantly whether or not there be any causal connexion between them; in other words "that modifications of consciousness emerge contemporaneously with corresponding modifications of nervous process" (Stout). The theory is the third possible alternative in considering the relation between mind and body, the others being interaction and one-sided action (e.g. materialism). It should be observed that this theory is merely a statement, not an explanation. (See PSYCHOLOGY.)