The illusion of reality: A review and integration of psychological research on hallucinations.

Abstract

Hallucinations are among the most severe and puzzling forms of psychopathology. Although usually regarded as first-rank symptoms of schizophrenia, they are found in a wide range of medical and psychiatric conditions. Moreover, a substantial minority of otherwise normal individuals report hallucinatory experiences. The purpose of this article is to review the considerable research into the cognitive mechanisms underlying (particularly psychotic) hallucinations that has been carried out and to integrate this research within a general framework. The available evidence suggests that hallucinations result from a failure of the metacognitive skills involved in discriminating between self-generated and external sources of information. It is likely that different aspects of these skills are implicated in different types of hallucinatory experiences. Further research should focus on specific metacognitive deficits associated with different types of hallucinations and on treatment strategies designed to train hallucinators to reattribute thoughts to themselves.

The role of schizotypy, mental imagery, and fantasy proneness in hallucinatory reports of undergraduate students

“…Such an impaired reality testing might foster misattribution of internally generated experiences, which in turn may promote hallucinatory reports (e.g. Bentall, 1990;Cahill & Frith, 1996). Indirect evidence for the idea of a specific response bias comes from studies finding a considerable overlap between fantasy proneness, schizophrenia-like phenomena, and dissociation (Merckelbach, Muris, Horselenberg, & Stougie, 2000;Merckelbach, Rassin, & Muris, 2000;Watson, 2001).…”

“…A number of authors have suggested that hallucinations exist on a continuum ranging from relatively benign forms to pathological manifestations as seen in schizophrenia (see review by Bentall, 1990). Indeed, several studies have indicated that a non-trivial minority of the normal population reports having had hallucinatory experiences at some point in their lives (e.g.…”

“…Bentall, 1990;Cahill & Frith, 1996), the involvement of mental imagery in hallucinations has proven to be a controversial issue. Using a signal-detection version of the White Christmas task, Bentall and Slade (1985a) investigated to what extent unusual vivid imagery may influence performance during an auditory detection task.…”

Altered time-perception performance in individuals with high schizotypy levels

“…Schizotypy refers to psychometrically-measured behavioral traits and dispositions associated with schizophrenia, but present in the non-clinical population [27][28] . The validity of schizotypy has been supported by factor analytical studies that have linked schizotypal traits to schizophrenic symptoms 29,30 .…”

Dissociative tendencies and individual differences in high hypnotic suggestibility

“…In contrast, LDHS participants have been argued to be more responsive to dreams and regressions and positive hallucinations profiles, which may require greater utilization of fantasy and imagery and depend upon strong episodic retrieval strategies (Barber, 1999;Hilgard, 1964). Alternatively, if the HDHS subtype is characterized by a monitoring deficit during hypnosis (Kunzendorf & Boisvert, 1996), they may be more responsive to hallucination suggestions because of impaired monitoring of the source of perceptual representations and the concomitant misattribution of the content to the environment (Bentall, 1990; see also Brown & Oakley, 2004). Finally, if HDHS participants possess a greater propensity for automatizing behavior and compartmentalizing information (Barber, 1999), they would be expected to exhibit greater responsiveness to the posthypnotic compulsions profile, which may depend on the execution of implementation intentions outside of awareness.…”