Source : FISH ’S Clinical psychopathology

Definitions

The definition of a hallucination as ‘a perception without an object’ has the advantage of being simple and to the point but is does not quite cover functional hallucinations. To cover these and to exclude dreams Jaspers suggested the following definition ‘a false perception which is not a sensory distortion or a misinterpretation, but which occurs at the same time as real perceptions’. SCAN (World Health Organization, 1998) defines hallucinations as ‘false perceptions’.

What distinguishes hallucinations from true perceptions is that they come from ‘within’, although the subject reacts to them as if they were true perceptions coming from ‘without’. This distinguishes them from vivid mental images that also come from within but are recognised as such. As with all abnormal mental phenomena, it is not possible to make an absolute distinction as the individual with eidetic imagery will examine his images as if they were external objects and some patients have sufficient insight to recognise that their hallucinations are not truly objective.

A great deal of discussion has raged about the concept of the ‘pseudohallucination’. Most of the statements are derived from the work of Jaspers (1962), who, first of all, distinguished between true perceptions and mental images. Perceptions are substantial; appear in objective space; are clearly delineated, constant and independent of the will; and their sensory elements are full and fresh. Mental images are incomplete; are not clearly delineated; are dependent on the will; exist in subjective space; are inconstant and have to be recreated. Pseudo-hallucinations are a type of mental image that, although clear and vivid, lack the substantiality of perceptions; they are seen in full consciousness, known to be not real perceptions and are located not in objective space but in subjective space (for example, inside the head).

Like true hallucinations they are involuntary. In his book General Psychopathology Jaspers (1962) gives two examples, one of a patient who hadtaken opium, making it unlikely therefore that the pseudo-hallucinationappeared in clear consciousness. The second concerned a patient with a

chronic psychotic illness who himself distinguished between hallucinatory voices in objective space and voices which he heard inwardly (pseudohallucinations).

Pseudo-hallucinations can be identified in the auditory, tactile or visual modalities.

The confusion over the meaning of ‘pseudo-hallucination’ stems from two different approaches to definition; one based on insight (Hare, 1973) and the other, as exemplified by Jaspers (1962), based on whether the image lies in inner or outer perceptual space. Jaspers believed that pseudo hallucinations are variants of fantasy/mental imagery and, thus not carrying the same diagnostic implications, are true hallucinations. Hare argued that since insight often fluctuates and at times is partial, it was more profitable to think in terms of degree of insight. This, however, renders the concept of pseudohallucinations largely superfluous. SCAN (World Health Organization, 1998) does not use the term pseudo-hallucination, but does have an item for rating insight and for whether the experience occurs inside or outside the head.

Jaspers insisted that there is no gradual transition between true and pseudo-hallucinations, but Fish, in a previous edition of this book (Hamilton, 1974) disagreed, citing an example of non-substantial hallucinations experienced in outer objective space; patients with substantial hallucinations

also experienced these in outer objective space but they recognised these as the result of their active vivid imagination. Thus, Fish argued, there is a continuum from pseudo-hallucinations to hallucinations. This is confirmed by the work of Leff (1968) on sensory deprivation and perception. He found that subjects could not always distinguish between images and hallucinations and concluded that the perceptual experiences of normal people under conditions of sensory deprivation overlap considerably with those of psychiatric patients.

The importance of pseudo-hallucinations is that their presence does not necessarily indicate psychopathology, unlike true hallucinations, which are indicative of serious mental illness. Although such a comment is found in many textbooks of psychiatry, its veracity must surely rest with the definition that is adopted, since, as Hare argues, if insight is the criterion and this fluctuates during illness, the meaning and relevance of pseudo-hallucinations becomes redundant.