For most psychologists, the topic of hallucinations immediately brings to mind the association with psychiatric disorders such as schizophrenia and post-traumatic stress disorder. The comprehensive text by Drs. Aleman and Larøi presents a much broader view of this phenomenon, looking at the many manifestations of hallucinations as the basis for the construction of a cognitive model to account for this phenomenon.
Chapter 1 is devoted to the development of a working definition of hallucinations. The authors examine historic accounts of hallucinations and the explanations offered for these experiences. This information provides context for discussion of the current range of definitions. For the remainder of the text, hallucinations are defined as a sensory experience that is vivid enough to be perceived as real, yet occurs without external stimulation of the corresponding sensory organ. Hallucinations are differentiated from illusions which involve external stimulation that is misinterpreted, yet hallucinations are tied to a continuum of sensory experience.
In Chapter 2, the authors describe hallucination presentations by sensory modality and content. They examine cultural factors and emotional factors, demonstrating how each of these factors shape hallucination incidence and content, as well as define where the experience falls on a continuum from valued or appropriate to feared or deviant.
Chapter 3 provides a comprehensive review of the adult and pediatric literature regarding the incidence of hallucinations. In addition to their occurrence in psychiatric populations (e.g., psychosis, post-traumatic stress disorder, post-partum depression), the authors also explore incidence in neurological disorders and in the context of sensory loss/deprivation. In contrast to these clinical populations, hallucination incidence is also reported for what the authors define as “nonclinical populations”. As the reader discovers, “nonclinical” does not necessarily refer to individuals free of significant situational stresses (e.g., loss of a loved one, past sexual abuse), precipitating behaviors (e.g., use of drugs, marijuana), or emotional symptoms (e.g., anxiety/depression). Some of the nonclinical populations might be better defined as individuals who have not sought mental health services. Based on data presented in Chapter 3, the authors propose that hallucinations are not a separate entity, different from normal experience, but rather are part of a continuum of experience. In Chapter 4, they present the initial framework of their theoretical model. They report literature involving language processing, attention modulation and perceptual expectations in individuals experiencing hallucinations and individuals not reporting hallucinations. The authors conclude that both sensory processing impairment (bottom-up factors) and perceptual expectation (top-down factors) contribute to the experience of hallucinations.
Chapter 5 further explores the top-down component by focusing on metacognition. Metacognitive models of hallucinations are explored through research on misattribution of speech, reality testing, reality monitoring, and inhibition in clinical and nonclinical populations. Some of the studies presented in this chapter involved multiple groups and/or multiple conditions. The addition of summary tables or graphics would have been helpful. This was also true of some studies presented in Chapter 3. In Chapter 6, research directly focused on brain activity is explored. The authors review the potential role of specific neurotransmitters in increasing or decreasing the probability of hallucination generation. Early brain stimulation studies, as well as recent functional neuroimaging studies are also reviewed.
Information presented to this point is integrated in a schematic model for the production of hallucinations and other sensory processing errors in Chapter 7. Targeted brain regions for mediation of components are identified. The resulting model provides multiple routes to the processing error(s) that culminate in hallucination production and hallucination content. This interesting model is offered as a framework for continued research. Chapter 8 is of primary interest to treating clinicians. The authors review available research into treatment approaches for individuals whose hallucinations are affecting quality of life. While medication and transcranial stimulation are briefly reviewed, the emphasis of the chapter is on cognitive-behavior approaches.
In the introduction to Hallucinations: The Science of Idiosyncratic Perception, the authors define a diverse target audience ranging from neurologist to psychotherapist, from students to clinicians and researchers. To some extent, the authors achieve their goal. They balance extensive details within chapters with “Chapter Highlights” that provide a brief concise summary of the key “take home points” from the material presented. While students may get lost in the details, the “take-home-points” will come to their rescue. The authors provide an appendix containing a description of many of the measures used in the research cited, some of which are also appropriate to clinical practice. Chapters 6 and 7 would be a difficult read for those unfamiliar with functional neuroanatomy. While the book has something of value to all included in the identified the target audience, it will be of particular interest to treating clinicians, those interested in pursing research in this area, and neuropsychologists dealing with neurological disorders, such as Parkinson's or dementia, which are associated with an increased risk for hallucinations.
