Occurrence and phenomenology of hallucinations in the general population: A large online survey

Hallucinations, traditionally examined in neurological, psychiatric, or somatic disorders, also occur in the general population with prevalence estimates around 6–15%. Theoretical models of sensory perception suggest that misperceptions (hallucinations, illusions, distortions) can be common byproducts of fast top-down processes enabling rapid perception. Studying hallucinations in non-clinical samples can elucidate underlying mechanisms while avoiding confounds common in clinical cohorts (medication, comorbidity). However, phenomenological characteristics in the general population are understudied, with prior work focusing on subpopulations or specific modalities/types. This study aims to characterize the phenomenology of hallucinations across four sensory modalities in a large general-population sample (14+ years) and to examine their association with delusions.

Prior epidemiological work reported general-population prevalence of hallucinations at 6–15%, but comprehensive phenomenology is scarce. Models of perception emphasize interplay between bottom-up sensory input and top-down predictions; misperceptions may arise from overweighting priors or failures of top-down control. Previous studies often targeted subgroups (students, elderly) or specific hallucination types (e.g., auditory verbal, hypnagogic/hypnopompic, olfactory) and have documented associations between hallucinations and delusions in the general population. The current study addresses gaps by broadly assessing phenomenology across modalities using the QPE, without restricting definitions to specific contents, durations, or insight criteria.

Design: Cross-sectional, observational online survey conducted in the Netherlands from September 2016 to May 2017. Ethics: Exempted from full review by the Medical Research Ethics Committee of the University Medical Center Utrecht (protocol 16-408/C). Participation: Open to individuals aged 14+ fluent in Dutch; informed consent obtained online; anonymous data collection; participants could withdraw anytime. Recruitment: National promotion via media and events through the ‘Weekend van de Wetenschap’ initiative; project website: https://zieikspoken.nl. Definition: Hallucinations broadly defined as perceptions without an external source; survey presentation emphasized recognizability of such phenomena to minimize stigma and encourage reporting. Measures: Self-report version of the Questionnaire for Psychotic Experiences (QPE) hallucination items for four modalities—auditory (AH), visual (VH), tactile (TH), olfactory (OH). Screening sequence per modality: lifetime occurrence; if yes, presence in past week; if not, presence in past month. Detailed phenomenology was assessed only if hallucinations occurred in the past week or month. Phenomenological items included: for AH and VH—frequency, duration, time of day, perceived location, emotional burden, ensuing distress, impact on daily functioning, insight, commands, interaction, and comorbid illusions; for TH and OH—frequency and relation to bothersome experiences; all four modalities included age of onset, relation to prior bothersome experiences, and open-ended content descriptions; additional multiple-choice content items for AH (voices) and VH (images). Delusions: Optional QPE delusion items assessed nine types (paranoia, reference, guilt, control, religious, grandeur, somatic, Capgras, Cotard). For each, lifetime presence was screened; if present in past week, conviction was rated. A thought was categorized as a delusion only if present in the past week with near-to-full conviction; then frequency, distress, and dysfunction were queried. Data handling and analysis: Entries and exclusions summarized in supplementary materials. Open responses were manually categorized by content; categories with ≤1% were grouped as 'other'. For descriptive summaries, phenomenological data from past-week and past-month reporters were merged. Group comparisons across four subgroups based on recency of hallucinations (never; >1 month ago; past month not week; past week) used Pearson’s chi-square (categorical), and one-way ANOVA or Kruskal–Wallis tests (continuous) depending on normality (assessed via Kolmogorov–Smirnov and visual inspection). Jonckheere–Terpstra tests assessed ordered trends. Analyses performed in IBM SPSS Statistics v22. Sample: 10,448 valid entries; optional delusion items completed by 6523 participants (62.4%). Demographics: median age 32 (IQR 23–47); 68.9% female; education skewed toward higher levels.

• Sample: 10,448 participants (age 14–88; median 32; 68.9% female). Optional delusions module completed by 6523 (62.4%).
• Occurrence (past month): AH 29.4% (n=3086), VH 21.5% (n=2248), TH 19.9% (n=2207), OH 17.3% (n=1807). Hallucinations in ≥2 modalities reported by 47.6% of those with past-month hallucinations; 19.5% in ≥3 modalities; 5.6% in all four modalities.
• Temporal prevalence (from discussion): lifetime 80.1%; past month 51.1%; past week 32.4% (using broad definitions and online self-report).
• Frequency: Majority experienced less than once per week (AH 69.3%; VH 65.1%; TH 69.7%; OH 78.6%); daily or more: AH 8.2%, VH 9.4%, TH 9.1%, OH 4.5%.
• Duration: Typically instant/seconds; longer durations also reported (AH ≥10 min: 7.4%; VH ≥10 min: 4.9%).
• Hypnagogic/hypnopompic: Around 9.0–10.6% reported occurrences when falling asleep or waking.
• Chronicity: Over half reported experiencing hallucinations for ≥10 years (AH 54.5%; VH 60.3%; TH 54.4%; OH 53.5%).
• Distress and impact: At least moderate distress from AH 10.5% and VH 16.8%; at least some impact on daily functioning from AH 12.7% and VH 17.3%.
• Insight: Reduced insight (near to fully convinced experiences were real) in AH 10.2% and VH 11.4%.
• Interaction/commands: Interaction with phenomena reported by ~45.7% (AH) and 54.9% (VH); commands present in a minority (AH 8.3%; VH 5.2%), with some compliance.
• Content examples: AH—voices 63.3% (including own name 29.5%, not specified 20.6%, full sentences 5.5%), music 18.3%, ringtones/doorbells 17.3%, mechanical human sounds 10.0%, alarms/sirens 4.8%; about 49.6% reported musical content at some time. VH—shadows 48.8%, people 34.4%, animals 19.2%, movement 22.2%, light 4.2%, colors 4.5%, patterns 2.3%. TH—being touched 44.8%, formication 23.4%, tickling/tingling 19.2%, sensed presence 7.1%. OH—fire 36.9%, food/drinks 14.8%, perfume 10.9%, flowers 9.6%, familiar/nostalgic scents 9.5%, gas 9.0%.
• Negative content and associations: Negative content common (AH 34.1% at least partially negative; VH 53.2% at least somewhat negative). Content associated with previous bothersome experiences in roughly 1/5–1/6 across modalities (14.8–20.2%).
• Bereavement phenomena: 2.8% of entire group reporting recent hallucinations endorsed grief-related experiences (e.g., hearing, seeing, feeling, or smelling a deceased person).
• Sensed presence: Reported by n=168/5335 among those with past-month hallucinations.
• Other misperceptions: Illusions reported by small subsamples (AH 2.8%, VH 6.0%, TH 0.3%, OH 0.6%); rare descriptions included visual distortions (e.g., prosopometamorphopsia), Gedankenlautwerden, musical tinnitus, déjà vu, migraine auras, drug-induced imagery, reperceptive hallucinations.
• Delusions: Among 6523 respondents to delusion items, 7.0% (n=454) reported delusions (past week, near-to-full conviction). Types most frequent: paranoia, reference, grandeur. Delusions were significantly more common with more recent hallucinations (χ²≈228, p<0.001): up to 13.4% in those with hallucinations in the past week.
• Demographic associations: More recent hallucinations associated with female gender, younger age, and lower education (all p<0.001 for trends across groups).
• Overall: Findings support a broad phenomenological continuum of misperceptions in the general population.

The study addressed the gap in knowledge regarding the phenomenology of hallucinations in the general population by comprehensively characterizing frequency, duration, content, insight, distress, functional impact, and multimodality across four sensory modalities. Results showed high rates of recent hallucinations using a broad definition and online self-report, substantial multimodal overlap, and meaningful subgroups with more severe features (e.g., distress, functional impairment, negative content, commands, reduced insight, and co-occurring delusions). The stepwise association between recent hallucinations and delusions replicates prior general-population findings and aligns with neurobiological models positing interactions between top-down priors and belief formation. The observed heterogeneity across all phenomenological items supports a continuum model ranging from fleeting, easily corrigible misperceptions (including illusions) to persistent, distressing hallucinations typically seen in clinical contexts. Content patterns frequently involved warning signals and social cues (e.g., sirens, footsteps, shadows, familiar people or scents), consistent with adaptive top-down prediction mechanisms. Clinically and scientifically, phenotypic subtyping based on phenomenology (regardless of diagnosis) may improve understanding of mechanisms and guide personalized assessment and intervention, while findings can aid destigmatization and psychoeducation.

This large online general-population survey provides the first extensive, cross-modal characterization of hallucination phenomenology in over 10,000 participants. Key contributions include documentation of high multimodal overlap, rich content descriptions (notably for tactile, olfactory, and non-verbal auditory hallucinations), a graded relationship between recency of hallucinations and delusions, and pronounced heterogeneity indicating a phenomenological continuum. Substantial minorities experienced distress and functional impairment. The study underscores the importance of incorporating detailed phenomenological assessments and subtyping in future research and clinical practice. Future work should expand to under-assessed phenomena (e.g., gustatory, sexual hallucinations, time distortions), refine discrimination from related experiences (e.g., earworms), include interviewer ratings where feasible, and integrate clinical determinants and biomarkers for deep phenotyping.

• Anonymous online design prevented direct verification of entry reliability; anonymity may have increased honest reporting.
• Sampling/response bias likely: topic salience may have attracted individuals with hallucinations; sample skewed toward younger and female participants; recruitment channels may have reached specific groups; incomplete entries not recorded; generalizability of demographic associations limited.
• Recall bias risk for lifetime and age-of-onset items; phenomenology limited to past-month reports to mitigate recall issues.
• Self-report QPE items for delusions and insight without interviewer corroboration may affect reliability.
• Scope limitations: gustatory, sexual hallucinations, and time distortions not assessed; less extensive phenomenology for TH and OH; illusions and distortions not directly screened; no specific item for pseudohallucinations due to definitional heterogeneity.
• No clinical determinants collected (medical history, medication), limiting context and ability to assess overlap with clinical populations.
• Potential false positives for specific contents (e.g., musical earworms vs musical hallucinations).