dissociation model of hallucinatory experience

   The term dissociation model is indebted to the Latin words dis (apart, away from each other) and associare (to gather, to unite). It refers to a hypothetical model introduced in or shortly before 1894 by the German hallucinations researcher Edmund Parish (1861-1916), which seeks to explain hallucinations in terms of perceptual input signals misdirected towards aberrant sensory cortical areas. The term dissociation is notorious for the wide range of meanings and connotations attached to it. The manner in which it is used in the context of the dissociation model of hallucinatory experience is based on the conventions of association psychology, which state that all mental activity is based on associations, and that regular paths ofassociation can become disrupted or diverted under the influence of certain pathological conditions. When applied to the subject matter of hallucinatory experience, the dissociation model suggests that sensory input signals are sometimes diverted in the direction of aberrant loci within the sensory cortex, thus initiating perceptual processes that do not match with the input stimuli involved. Parish seeks to explain hallucinations by a virtually exclusive appeal to this type of dissociation. To account for all types of * sensory deception, he divides dissociation into total and partial dissociation, with a further division of the latter subclass into systematic partial dissociation, localised partial dissociation, and diffused partial dissociation. In all of these cases, however, he attributes the mediation of hallucinations to a blocking of the regular course of sensory input signals by what he calls "a state of intracerebral tension". This intrac-erebral tension is conceptualized by Parish in terms of psychological preoccupations that lend the concomitant brain area an 'attractor' function, thus causing the affected individual to hallucinate in accordance with his or her idiosyncratic, affect-laden themes. In Parish's own words, "A false perception occurs when for some reason or other the cerebral elements are in such a state of tension that the incoming stimuli stream towards element-groups which normally would be discharged only by stimuli of another kind." Modern variants of the dissociation model of hallucinatory experience are known under names such as * biased competition, * top-down attentional factor, and cross-activation. The literature on * bereavement hallucinations, for example, refers to biased competition as an important candidate mechanism for the perception of a deceased loved one (rather than some random image) by widowed individuals, whereas the literature on * coloured hearing and other types of * synaesthesia designates cross-activation between different sensory domains as one of its major explanatory models. Some important virtues of the dissociation model of hallucinatory experience are its close connection with the biomedical model of sense perception, and its capacity to link the specific contents of hallucinations to the realm of personal, qualitative experience. Thus it is well suited to explain the mediation of hallucinations charged with idiosyncratic and symbolic meaning, as is the case in many instances of * reflex hallucination. Whether it is suited to explain all, or even a large number of hallucinatory experiences, is food for discussion.

   References

   James, W. (1986). Review of Zur Kritik des telepathischen Beweismaterials and Hallucinations and illusions, by Edmund Parish (1897). In: Essays in psychical research. Edited by Burkhardt, F., Bowers, F. Cambridge, MA: Harvard University Press.

   Locke, J. (1995). An essay concerning human understanding. New York, NY: Prometheus Books.

   Parish, E. (1897). Hallucinations and illusions. A study ofthe fallacies ofperception. London: Walter Scott.

   Rees, W.D. (1971). The hallucinations of widowhood. British Medical Journal, 4, 37-41.

   Wernicke, C. (1900). Grundriss der Psychiatrie. Leipzig: Verlag von Georg Thieme.