qualia theory of hallucinations

   The term qualia theory is indebted to the Latin term qualia, which is plural for the singular quale; it translates as 'qualities'. The term qualia theory is used by the British philosopher Tim Crane to denote any philosophical theory that puts the subjective qualitative properties of hallucinations on a par with those of regular sense perceptions, arguing that the final common pathway of both types of perception involves the instantiation of qualia. As used in philosophy, the term qualia refers to the subjective qualities of conscious experience. Examples of qualia are the redness of red apples, the way honey tastes, the way lovesick-ness feels, and the way a diesel engine sounds. The term qualia theory is used in opposition to the term disjunctivist theory or *disjunctivism. In conformity with the empiricist philosophy of John Locke (1632-1704), and contrary to the dis-junctivist theory, the qualia theory suggests that sense perceptions and subjectively indistinguishable hallucinations are states of the same fundamental psychological kind, because both types of perception ultimately depend on the instantiation of qualia. An important advantage of the qualia theory is that it is compatible with current neuro-scientific hypotheses involving the role of the perceptual system in the mediation of both hallucinatory and sensory percepts. As suggested by the American neuroscientists Rodolfo Riascos Llinâs (b. 1934) and Urs Ribary, both hallucinations and sense perceptions may be considered closed, intrinsic functional states of the thalamocortical system. The qualia theory fits in well with this hypothesis, as both positions emphasize the view that mind-independent objects as such cannot be perceived, and that instead we perceive endoge-nously mediated qualia, irrespective of their true origin from inside or outside the brain (or mind, in a dualist reading). An important disadvantage of the qualia theory is that it compromises the status of regular sense perceptions. After all, if there are no intrinsic qualitative differences between sense perceptions and hallucinations, how are we to tell the difference between the two types of percepts? A post hoc solution to this problem can be found in the work of the British psychiatrists Ralph-Peter Behrendt and Claire Young, who suggest that the senses exert a restraining influence upon the number of degrees of freedom of the thalamo-cortical system's spontaneous (hallucinatory) activity. A consequent elaboration of this line of thought entails the view that all our percepts are hallucinations, and that sense perceptions have the status of hallucinations that are merely modulated or restrained by the senses. Or, as the French critic and historian Hippolyte Taine (1828-1893) put it as far back as 1870, that sense perceptions are true hallucinations (La perception est une hallucination vraie).

   References

   Behrendt, R.P., Young, C. (2004). Hallucinations in schizophrenia, sensory impairment and brain disease: A unifying model. Behavioural and Brain Sciences, 27, 771-787.

   Crane, T. (2006). Is there a perceptual relation? In: Perceptual experience. Edited by Gendler, T.S., Hawthorne, J. Oxford: Clarendon Press.

   Llinâs, R.R., Ribary, U. (1994). Perception as an oneiric-like state modulated by the senses. In: Large-scale neuronal theories ofthe brain. Edited by Koch, C., Davis, J.L. Cambridge, MA: MIT Press.

   Taine, H. (1870). De l'intelligence. Tome 2. Paris: Librairie Hachette et Cie.