A multidisciplinary working group reviewed evidence on the similarities and differences between hallucinations induced by psychedelics and those occurring in schizophrenia-spectrum disorders, examining data from pharmacology, brain imaging, phenomenology, and anthropology. The authors highlight both shared features and distinct characteristics across these scales, and attempt to integrate findings using computational approaches. They conclude with recommendations for future research, emphasizing the need for further study to clarify the relationship between these types of hallucinations.
Trauma can contribute to voice-hearing but is not necessary for it. This article uses ethnographic and other data to show multiple pathways to voice-hearing in both clinical and nonclinical populations, excluding known causes like drugs or epilepsy. Trauma sometimes plays a major role, sometimes a minor role, and sometimes no role at all. Distinct phenomenological patterns in voice-hearing may reflect different salience of trauma for those who hear voices.
Hypnagogic and hypnopompic hallucinations (HHHs) are common in the general population, with auditory HHHs occurring in 6.8% of people, multimodal HHHs in 12.3%, and out-of-body experiences at sleep onset/offset in 32.2%. Individuals who experience only auditory HHHs report less frequent, less disturbing, and more neutral hallucinations, with less influence on behavior and social life, compared to those who also have daytime hallucinations. They also score similarly to non-hallucinating individuals on mental health, anxiety, childhood happiness, and wellbeing measures. The average age of first onset for purely auditory HHHs is 28.2 years, later than for daytime-only (20.9 years) or combined groups (19.1 years).
Hallucination prevalence decreases with age across all sensory modalities—auditory, visual, olfactory, and tactile—as well as for sensed presence and hypnagogic/hypnopompic types. In a large representative Norwegian sample, young adults (19–30 years) reported the highest rates, middle-aged (31–60) intermediate, and older adults (61–96) the lowest. Anxiety partially mediated this age effect, while depression acted as a partial suppressor. Co-occurrence of auditory and visual hallucinations was minimal across all age groups. The general population reports a wider variety of hallucination modalities than is typically seen in clinical populations.