Jason W. Brown
Over the years from Esquirol to Henri Ey ( 1973) many works on hallucination have appeared. For the most part, these are accounts of hallucinations in schizophrenia or states of delirium and drug intoxication, really little more than a catalog of hallucinatory forms with no attempt to relate the hallucination to perceptual physiology or regional brain function. The result has been a complex phenomenology, a few pseudo-theories, a lack of neurological hypotheses and much scholarly disputation. The one thing that is clear from this work is that an approach to the problem of hallucination should be grounded, not in the symptom content, which is too rich for interpretation, but on patterns of hallucinatory experience. If such patterns can be identified, and can be shown to correspond with damage to specific brain areas, they may be comprehensible in terms of a general theory of perception ( Brown 1983b).
The search for these patterns is not an easy matter, for there are many different and seemingly unique forms of imagery. Yet, all image phenomena overlap in some characteristics. A memory or a thought image and an eidetic image share the feature of an active volitional character, while the eidetic and after-image occur in relation to an external object. An hallucination, an eidetic, and a dream image may have the same content. The after-image enlarges according to the viewer's distance from the projection surface, but this also occurs in the early stages of alcoholic hallucinosis ( Morsier 1938). After-images share with phosphenes or elementary visual hallucinations the characteristic of displacement with eye movements (Brindley and Lewin 1968). Objects and, in my experience, thought images may move slightly in a direction opposite a shift in gaze. Displacement does not occur for eidetic images and hallucinations. However, attempts to scan, fixate, or attend to an hallucination may result in its disappearance. This is not simply a____________________