In 1907 the Swiss psychiatrist Carl Gustav Jung (1875-1961) defined hallucinations as follows: "Hallucination is simply the outward projection of Psychic elements."
References
Jung, C.G. (1907). The psychology ofdementia praecox.In: C.G. Jung. The collected works. Volume three. The psychogenesis of mental disease. (1977). Translated by Hull, R.F.C. Edited by Read, H., Fordham, M., Adler, G. London: Routledge & Kegan Paul.
Dictionary of Hallucinations. J.D. Blom. 2010.