Deri states that almost everything essential to the understanding of the ego was present in Freud's 1895 paper, Project for a Scientific Psychology. In The Interpretation of Dreams, Freud retreated from the neurophysiological model of the mind with emphasis on earliest development, to a psychological model of the mind with an emphasis on later development. He may have been led to do this by oedipal problems revealed in his self-analysis, oedipal conflicts of his patients, and the scientific atmosphere of the time. This shift resulted in an erroneous concept of a passive and weak ego. Deri argues against a purely psychological model of the ego that disregards the psychosomatic integrity: the ego functions in the context of a psychobiological organism.