Geoffrey Rose's big idea.

tions, which the subject recognises as arising from his or her imagination.'8 19 Dissociative (conversion) phenomena may account both for these pseudohallucinations and for many spiritual and paranormal phenomena.820 A dissociative mechanism may also underlie memory flashbacks (which may be experienced as real2) in post-traumatic stress disorder.22 Dissociative experiences may even be normal.8 Isolated hallucinations may be common and normal perceptual errors and no more indicative of psychiatric illness than isolated illusions. But, whether we describe visions and voices as psychotic, dissociative, hypnagogic, or normal, uncertainties remain about their underlying psychophysiology and the relations between these seemingly very different states of mind. FRANCES KLEMPERER Senior Registrar in General Psychiatry, Bexley Hospital, Bexley DA5 2BW