This review examined the hypothesis that mental imagery vividness can be used as a predictor of hallucinatory experience. Earlier studies provided supporting evidences to this hypothesis, showing hallucinating population has higher mental imagery vividness comparing to nonhallucianting population. However, as a result of varied operationalization and measurements of mental imagery, contradicting results abound, showing no significant difference of mental imagery vividness between halluciantors and nonhallucinators. No clear evidences can be used to determine whether the hypothesis is valid or not so far. On the other hand, development of neurological studies provided a new perspective for looking into the relationship between mental imagery and the experience of hallucination.
Keywords: mental imagery vividness, hallucination, schizophrenia
Mental Imagery Vividness as a Predictor of Hallucination: A Literature Review Mental imagery, as defined by Finke (1989), is an experience significantly resembling that of perceiving, but it occurs in the absence of an adequate physical stimulus. It exists in all of the seven sensory modalities, such as visual, auditory, and olfactory (Thomas, 1999). Mental imagery is believed to be in close relationship with some core psychological mechanisms such as perception and memory, and holding its unique role in contributing to cognitive performance (Kosslyn, 1994). For example, evidences suggested that visual imagery ability predicts visuospatial memory performance (Kail, 1997). Hallucination is an experience that largely resembles mental imagery, because of its perceptual nature as well as absence of appropriate stimuli (Sack, Van de Ven, Etschenberg, Schatz, & Linden, 2005). Nevertheless, the two distinguish from each other by the individual’s ability of voluntary control, as well as his/her ability to determine the source of the experience. Specifically, mental imagery is generally regarded as being actively generated and can be intentionally controlled, while hallucination is most times beyond intention and control. The operator of mental imagery is usually aware of its internal source, while not necessarily so hallucinator. (Bentall, 1990). Hallucination, especially the form of auditory verbal hallucinations (AVH), is an important hallmark of schizophrenia (Wible, 2009). AVH is the perception of voices in the absence of sensory input. AVH has distinct clinical significance, as it affects about 70% of patients with schizophrenia (Sartorius et al., 1978; Silbersweig & Stern, 1996). Furthermore, there have been increasing evidences supporting that hallucination is not a rare case in non-clinical population, either. It is now believed to exist on a spectrum from comparably innocuous forms in non-clinical population to a more pathological manifestation in schizophrenics (see review by Bentall, 1990). Because of its significant implication in psychopathology, continuous work has been going on to find out the risk factors and predictors for hallucination. The relationship between mental imagery and hallucination has interested researchers for long because of their shared features. Among all the characteristics of mental imagery that are potentially related with hallucination, vividness has been most substantively examined. This review summarized theories and empirical evidences for the relationship between mental imagery vividness and hallucination. Although still in its budding stage, relevant neurological evidences were also examined. Theoretical Models
Vividness of mental imagery can be defined as the degree of perceptual detail experienced when having a mental image (Oertel et al., 2009). It has been associated with hallucination and schizophrenia for decades. In 1883, Galton suggested that increased vividness of mental imagery might be associated with hallucinatory experiences (as cited in Aleman, Böcker, & de Haan, 1999). Later in the 20th century, West...