Understanding the Development of Delusions: Relationships to Hallucinations and Social Identification in Psychosis

Systematic review:

Objectives: Cognitive theories of delusion formation in psychosis suggest that hallucinations may precede and precipitate delusional beliefs. Predictive coding accounts instead propose bidirectional relationships between these symptoms. To establish the relationship between both symptoms in early psychosis, we conducted a systematic narrative review of the prevalence and order of onset of hallucinations and delusions in individuals with First Episode Psychosis (FEP) or Clinical High Risk (CHR) status.

Methods: A search of three databases (PsycINFO, PubMed and Scopus) using terms relating to delusions, hallucinations and early psychosis identified 22 studies (N = 6946) reporting either the proportion of participants with clinically significant hallucinations and delusions, or the order of onset of each symptom.

Results: Despite heterogeneity in assessment methods and populations, delusions were consistently more prevalent than hallucinations. The proportion of patients reporting delusions without hallucinations consistently exceeded the proportion reporting the reverse pattern. Where order of onset was assessed, concurrent onset within one month was the most common finding, although delusions occurred as a first symptom more frequently than hallucinations.

Conclusions: Hallucinations and delusions tend to develop concurrently; however, delusions were more commonly reported in the absence of hallucinations than vice versa. Order-of-onset studies found that hallucinations did not consistently precede delusions. The results challenge theories proposing that unusual perceptual experiences are necessary precursors to delusional beliefs. The relationship between the symptoms may be bidirectional, as suggested by predictive coding accounts, although further research is needed to determine the interactions between these symptoms.

Empirical Project:

Objectives: Social groups often form on the basis of shared beliefs, and identification with social groups promotes norms regarding belief content. Weaker identification with groups may lead to increased vulnerability to developing unshared beliefs, such as delusions. This study investigated whether individuals with delusions have weaker identification with social groups, and whether this reflects difficulties tracking when beliefs are shared with others, or with forming affiliations on this basis.

Design: A cross sectional quasi-experimental study involved participants with clinical delusions (DEL), non-psychotic mental health problems (MH) and a control group with no mental health problems (CON)

Methods: Participants completed quantitative measures assessing clinical status and Social Identity Richness (SIR). A subsample of the DEL and CON groups completed an online Belief Alignment Task (BAT), which assessed the tracking of beliefs and the formation of social identities on the basis of shared beliefs of varying psychological salience.

Results: The DEL group reported significantly weaker overall social identification, and identification with proximal social groups, than both the MH and CON groups, after controlling for demographic variables. No significant differences were detected between the DEL and CON groups in their ability to track shared beliefs or form attachments on this basis.

Conclusions: Delusions may be associated with weakened identification with social groups. This may not reflect difficulties with tracking shared beliefs or forming affiliations with others. The role of social identity in the formation of unshared beliefs warrants further investigation.