**3. Future research directions**

#### **3.1. Toward differentiated and empirically founded categorizations of PLE**

A generally agreed upon and empirically substantiated categorization of PLE would be a helpful tool for clinicians as well as researchers. For example, it might help to provide more accurate screening procedures, predict risk for certain disorders featuring psychotic symptoms, facilitate more adequate treatment, and counteract stigmatization [29]. Further, it might also help to integrate findings across studies implementing different psychometric instruments and conceptualizations of PLE.

PLE ("symptoms" vs. attenuated versions thereof), as well as their rating format. Importantly, choosing one instrument over the other may profoundly affect the ensuing results [25]. For example, although similar sex differences have been found in non-clinical samples as in schizophrenic patients [72, 73], the non-detection of sex differences in a community sample has led researchers to conclude that they only present themselves in full-blown psychosis but not in sub-threshold states [74]. Interestingly, using a sample of healthy individuals, a study could replicate the detection and non-detection of sex differences in the latter studies, depending on the scales for PLE that were being analyzed [44]. It was suggested that scales including fewer and more severe or difficult items (e.g., someone has power over your thoughts [75]) might not be able to detect sex differences in healthy individuals, whereas scales inquiring more and attenuated experiences might do so (e.g., I have sometimes felt that strangers were reading my mind [41]). Importantly, different populations across the psychosis continuum ranging from non-disordered schizotypes, to prodromal patients, to patients with a schizotypal personality disorder, and to psychotic patients might all experience positive(-like) symptoms such as odd beliefs. However, these groups might differ regarding the relative prevalence of increasingly severe forms of experiences ranging from magical thinking to full-blown delusions [24]. Hence, depending on the sample, the research question, as well as the theoretical

model of psychosis, some surveys might be more adequate to be used than others.

**3.1. Toward differentiated and empirically founded categorizations of PLE**

A generally agreed upon and empirically substantiated categorization of PLE would be a helpful tool for clinicians as well as researchers. For example, it might help to provide more accurate screening procedures, predict risk for certain disorders featuring psychotic

operationalizations.

**3. Future research directions**

10 Psychosis - Biopsychosocial and Relational Perspectives

In addition to the mostly non-transparent choice of instruments [34] and their heterogeneous designs, unclear content validity of scales may additionally entail mixed results across studies and contribute to a blurred picture of psychosis [25]. Studies investigating symptom-level associations have applied multiple regression modeling to account for overlapping variance between different PLE scales in order to gain insight into their specific psychopathological significance [29, 30]. Whereas these results are meaningfully interpretable, the reliability of the interpretations ultimately depends on the choice of instruments and the (content) validity of the applied scales. Notably, scales measuring certain PLE may often conflate different constructs impeding a reliable interpretation of results, as exemplified by the MIS [24, 46]. Additionally, the emergence of ever-new concepts and terms as well as the interchangeable use of different terms for PLE with overlapping but not necessarily identical meanings has resulted in a "near Babylonian speech confusion" that hinders clarity in the nomenclature, blurs sources of inconsistencies between findings and constricts their interpretation [24, 32, 36]. Hence, to successfully elucidate the complex structure of psychosis, researchers should have detailed knowledge of existing constructs and be familiar with the limitations of their More recently, similar categorizations of three basic types of PLE have been proposed, suggesting that: (1) some indicate a specific vulnerability toward psychosis while (2) others might be non-specific and also be implicated in the development of affective disorders, and (3) some might not be associated with any clinical disorder at all [30, 39]. It has been speculated that some PLE such as paranormal beliefs are benign and might explain why they are mostly not associated with mental illness [32]. In contrast, it has been suggested that PLE specifically associated with distress and poor functioning might be more likely to indicate vulnerability to psychotic disorders [30]. However, it yet remains to be clarified to which category certain PLE should be assigned [32].

Recently, to shed light onto possible categorizations of PLE, a study investigated unique associations of certain PLE with subclinical symptoms relevant for psychosis spectrum disorders [76], i.e. negative-like symptoms, affective symptoms (anxiety, depression), and other psychological difficulties in a sample of healthy adults [28]. Referring to the model introduced above, following categorizations are suggested: Paranoid-like experiences in healthy individuals might specifically indicate vulnerability to psychosis (category 1), as they were the only significant predictor of schizophrenia-like negative symptoms (physical anhedonia, no close friends, and constricted affect) but were not associated with any type of affective symptoms. In contrast, hallucination-like experiences were uniquely associated with experiences from the anxiety spectrum (e.g., phobic anxiety, obsessive-compulsive symptoms) but not with negative-like symptoms. Further, ideas of reference were a positive predictor of anxiety symptoms and depressive symptoms. Therefore, the latter PLE might belong to the category of non-specific PLE, hence, predisposing toward affective and psychosis spectrum disorders (category 2). Lastly, paranormal beliefs and PAGE-R odd beliefs did not positively predict any of the subclinical difficulties, which might reflect that they are not associated with any clinical disorder at all (category 3). The latter categorization was underlined by the observation that paranormal beliefs and odd beliefs were negatively associated with various psychological difficulties. Notably, these findings raise the question if more categories for PLE might be needed that account for associations of PLE with well-being and stronger resilience [51, 64] and lower load of negative-like symptoms. However, it remains to be determined if these findings can be accommodated within a framework encompassing three classes of PLE.

The tentative categorization of PLE presented above requires more data and replications in samples representative of the healthy general population. Ultimately, longitudinal studies are needed to determine if specific PLE predict certain psychosis spectrum disorders more likely than other diagnoses and how they are implicated in the maintenance of mental health. Notably, other symptom factors that are relevant for determining the psychopathological significance of PLE were not regarded. Amongst other factors, these include intrusiveness, distress, and frequency of experiences as well as the associated development of functional impairment [47]. Furthermore, similar analyses are needed including other subclinical difficulties that might be part of the psychosis phenotype [16], such as disorganized symptoms and mania [51].

### **3.2. Toward a comprehensive assessment of psychotic-like experiences**

A comprehensive and phenomenological differentiated description of psychotic-like experiences (PLE) might be the prerequisite for attaining reliable classifications of PLE and new insights regarding their individual roles in the exacerbation of subclinical symptoms and the maintenance of mental health [34, 35].

For example, the PAGE-R item referring to perceiving thoughts and feelings of others might not only capture an attenuated version of a Schneiderian first-rank symptom of schizophrenia

Subtypes of Psychotic-Like Experiences and Their Significance for Mental Health

http://dx.doi.org/10.5772/intechopen.78691

13

Psychosis research has tended not to differentiate between subtypes of psychotic-like experiences (PLE) and to hold a predominantly deficit-oriented perspective on them. However, studies indicate that PLE might fundamentally differ regarding their individual psychopathological significance and risk for psychosis spectrum disorders. These results require further (longitudinal) investigations aiming at the creation of an empirically founded and accurate categorization of PLE. Importantly, new instruments featuring PLE not derived from clinical symptoms including positive valence ratings might contribute to a more accurate and comprehensive description of subclinical psychosis. Ultimately, these steps might help to advance psychosis research in explaining why some individuals with PLE become ill while others do not and could contribute

to more precise risk screenings and more effective therapeutic strategies in the long run.

The author thanks Prof. Gerd Folkers for his kind support and for providing the funding of this open-access book chapter. Further thanks go to Dr. Thomas Wyss, Dr. Diana Wotruba, Dr. Helene Haker, and Prof. Wulf Rössler for their collaboration in the research project

Department of Humanities, Social and Political Sciences (D-GESS), Collegium Helveticum,

"Exceptional Experiences, Salience and Dopaminergic Neurotransmission."

Swiss Federal Institute of Technology in Zurich (ETHZ), Zurich, Switzerland

Address all correspondence to: unterrassner@collegium.ethz.ch

This chapter was funded by Prof. Gerd Folkers, ETH Zurich.

(thought transmission) but just as well an individual's ability to empathize with others.

**4. Conclusions**

**Acknowledgements**

**Conflict of interest**

None.

**Thanks**

**Author details**

Lui Unterrassner

The clinical perception that psychosis presents itself as "cases" in need of treatment has profoundly shaped the way the psychosis phenotype is conceptualized in the current classification systems [15]. Consequently, this has also influenced the way PLE are operationalized across various psychometric instruments (e.g., be it as psychotic "symptoms" or their attenuated equivalents) [25]. However, there is evidence indicating that the phenomenological quality of psychotic experiences may differ between healthy and clinical individuals [28, 77]. Further, it might be argued that there are experiences belonging to the PLE spectrum that may not have been sufficiently regarded in research. In this context, the novel PAGE-R questionnaire assessing "exceptional experiences" is worth mentioning, as its items are not derived from clinical symptoms but are based on reports from individuals from the general population seeking advice due to their experiences [50]. Indeed, a recent study suggested that EE in healthy individuals can be meaningfully integrated into positive-like symptomatology while potentially expanding the existing description of PLE [44]. Importantly, the PAGE-R might capture more subtle PLE that are often not considered in psychosis research, such as sleep-related perceptions [4, 20] or enriching delusion-like experiences [45, 78]. At the same time, it focuses on experiences and does not include beliefs in the paranormal that might be less relevant for the study of subclinical psychosis [31, 54]. Interestingly, factor analyses suggested the presence of three types of experiences that paralleled the basic structure of the CAPE positive dimension [48], encompassing odd beliefs (*cf*., delusional ideations), dissociative anomalous perceptions (*cf*., bizarre experiences) and hallucinatory anomalous perceptions (*cf*., perceptual anomalies). Importantly, this finding indicated that PLE basing on clinical observations and PLE basing on reports of unusual experiences by the general population might represent overlapping and complementary facets of positive psychotic symptomatology. Indeed, current research suggests that the PAGE-R might provide a more differentiated picture of PLE and new information on their associations with indicators of disadvantage and well-being as well as etiological risk factors [28, 64].

However, the PAGE-R was originally not created to study PLE, but a construct referred to as "exceptional experiences" (EE, see [50]). More specifically, its representativeness for PLE in healthy states might be questioned, as individuals reporting EE are characterized by diverse psychological problems [79] and the selection and design of items are substantially influenced by the underlying concept of EE. However, the PAGE-R is currently under further development (Fach, pers. comm.). Nonetheless, its use in psychosis research might be a first step in the right direction regarding a more comprehensive assessment of PLE, as the PAGE-R is not restricted to experiences derived from clinical symptoms and inquires comfort that the experiences may confer and the context in which they occurred (e.g., during meditation). Both might be important but mostly neglected factors for evaluating the clinical relevance of certain PLE. However, pursuing this "non-clinical" approach, psychosis research might tap into supposed indicators of subclinical psychopathology that might as well measure healthy and socially desired abilities. For example, the PAGE-R item referring to perceiving thoughts and feelings of others might not only capture an attenuated version of a Schneiderian first-rank symptom of schizophrenia (thought transmission) but just as well an individual's ability to empathize with others.
