Cognition in Relation to Non-Auditory or Multisensory Hallucinations in Schizophrenia-Spectrum Disorders: A Scoping Review

Multisensory hallucinations refer to unusual perceptual events in the absence of corresponding stimuli, experienced in two or more sensory modalities. Within the schizophrenia-spectrum disorder literature, the cognitive correlates of multisensory and non-auditory hallucinations remain largely unknown. This scoping review aimed to map and synthesise research that explored relationships between cognition and non-auditory and multisensory hallucinations in schizophrenia-spectrum disorders. Published, peer-reviewed, empirical research studies were sought through three databases: Web of Science, Scopus, and PubMed. Studies that had explored visual, olfactory, tactile, and gustatory hallucinations, or multisensory hallucinations, and their relationships to any basic cognitive mechanisms were included. Of 2218 records identified, a total of 17 studies met inclusion criteria. Visual hallucinations were the most frequently explored (13 studies); followed by olfactory hallucinations (five studies), tactile hallucinations (two studies) and multisensory hallucinations (two studies). Several cognitive mechanisms were studied, yet the majority were only explored in individual studies across the sensory modalities, limiting conclusions that could be drawn. Exploring the potential mechanistic drivers for hallucinations across multiple sensory modalities would advance the field significantly and allow for development of aetiological models that better capture the full gamut of hallucinatory experiences.