Cutting^) defines hallucinations as 'perception without an object (within a realistic philosophical framework) or as the appearance of an individual thing in the world without any corresponding material event (within a Kantian framework)'. There is a problem with this definition. Although some hallucinating patients mistake a hallucinatory perception for a realistic one, others can differentiate them; there is an 'as if' quality even when patients assert that they perceive real objects or events. This was demonstrated experimentally by Zucker.(6) Voices described in detail by hallucinating patients were meticulously imitated and presented to the patients without warning. The patients had no difficulty in discriminating these external voices from their hallucinations. For this reason Janzarik (7) defined hallucinations, without associating them with perception at all, as 'free running psychic contents' (using a concept similar to Jackson's disinhibition). In keeping with this idea, lack of perception may facilitate hallucinations as in sensory deprivation or in the oneiroid states of paraplegic patients. (8)
There are gradual transitions of the perceptive quality of hallucinations from similarity to sensory experiences, as in delirium, to the bizarre apprehensions of some schizophrenics. Also, the extent to which the person is affected by the hallucination varies widely from descriptions of hallucinations as film-like in amphetamine psychoses to the affectively overwhelming experiences of hallucinations associated with delusional mood.
The term pseudohallucination is sometimes used when the hallucinations are recognized as unreal. Jaspers(9) defined hallucinations as corporeal and tangible (Leibhaftigkeit); pseudohallucinations lack this quality. According to Jaspers, pseudohallucinations are not as tangible and real as hallucinatory perceptions, they appear spontaneously, they are discernible from real perception, and they are difficult, but not impossible, to overcome voluntarily. Kandinsky illustrated Jaspers' definition of pseudohallucinations with a case example. Spontaneously arising images of acquaintances arose when the patient kept his eyes closed. He was fully aware of the unrealistic character of this experience and could abandon it by opening his eyes. Thus, to Jaspers, pseudohallucinations are close to imagined images except that they arise spontaneously and are more vivid. Jaspers' definition is not used consistently in the literature. In the Anglo-American literature it is sufficient for the definition of pseudohallucination that there is subjective awareness that the percept lacks a real external equivalent and arises from the subject's mentation.
The term imagery describes vivid visual experiences which can be produced and manipulated voluntarily. Imagery occurs in trance states when the perceptions are produced voluntarily, but become more real and last longer than imagery occuring in a normal state of mind.
Illusions differ from hallucinations in being based on a percept of a real object or event, which is misinterpreted, usually in accordance with a mood or special theme. Illusions have to be distinguished from delusional perceptions which are percepts based on real objects to which a wrong meaning has been attached. In delusional perceptions this 'error' cannot be corrected by the patient; in illusions the true meaning can be recognized eventually.
Kurt Schneider described Gedankenlautwerden (also called écho de la pensée, or thoughts becoming aloud) as a transitional phenomenon between very vivid imagination, thoughts that are difficult to control, and auditory hallucinations. This concept is identical with that of pseudohallucinations as used in the Anglo-American literature. The patient can recognize that the words he hears are his own thoughts, but he cannot voluntarily turn them on or off. Gedankenlautwerden can interfere with thinking, for example disturbing concentration when talking to other people. Gedankenlautwerden can be differentiated from thought insertion by, for example, God or Satan, which can be distinguished from the person's own thoughts but need not be a hallucination. Gedankenlautwerden also differs from auditory hallucinations in that there is a lesser degree of alienation.
Klosterk6tter(19 has described transitions from elementary unformed hallucinatory sensations, like a crack, bump, or hiss, through more meaningful perceptions which still can be localized 'inside' the head, to complex hallucinations which become part of a delusional cognitive structure. These transitions were related to increasing affective involvement in the themes of the hallucinations. Klosterk6tter's observations support Janzarik's interpretation of hallucinations as 'free running psychic contents', as do experimental studies of model psychoses which show a regular sequence of three psychopathological states: vegetative arousal, affective change, and 'productive' phenomena like hallucinations and delusions.
Some misperceptions, found mainly in schizophrenic patients, are less complex than hallucinations, appear to be more closely related to neuropsychological disturbances, and include less systematization. They include optical distortions of size, colour, distance, and perspective, which can resemble experiences reported by people taking cannabis or other psychoactive drugs. These fluctuating circumscribed misperceptions are included in Huber's basic symptoms. They exemplify the way in which a more complex phenomenon of psychopathology can be built upon something more basic. Krause et al.(H) videotaped the non-verbal behaviour of schizophrenic patients and their healthy partners in a conversation. Very brief non-verbal cues play an important part in a dialogue, for example signalling a change of speaker or forming a non-verbal comment on the other person's words. Schizophrenic patients miss these non-verbal brief cues and are poor at judging the intentions of others; their own non-verbal communication is poorly co-ordinated. The ensuing dysfunction diminishes social competence. Schizophrenic painters who have been highly trained before the onset of their illness have been shown to misperceive erspective. (12)
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