A term introduced in or shortly before 1973 by the American ophthalmologist David Glendenning Cogan (1908-1993) to denote a type of hallucinatory activity which is due to the release of perceptual material from 'lower' regions of the brain. Cogan opposes this type of hallucinatory activity to the "irritative form, in which hallucinations arise from local epileptiform (or irritative) activity. For a further explanation of the release model, see the entry Perceptual release theory of hallucinations.
References
Cogan, D.G. (1973). Visual hallucinations as release phenomena. Albrecht von Graefes Archiv für Klinische und Experimentelle Ophthalmologie, 188, 139-150.
Dictionary of Hallucinations. J.D. Blom. 2010.