bioRxiv : the preprint server for biologyOct 8, 2026

Ongoing unusual perceptions in psychedelic users are linked to learned hallucinations and weaker sensory processing

Psychedelic Science Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Oct 9, 2026

Abstract

Surveys of 186 naturalistic users of serotonergic psychedelics reveal that past and current perceptual abnormalities are linked to younger age at first use and higher doses.

Participants showed a higher rate of visual conditioned hallucinations and greater confidence in their perceptions.
Lower visual thresholds were associated with a history of perceptual abnormalities.
Reduced decision precision was identified as a key factor linking dosage to perceptual abnormalities.
The relationship between sensory evidence and prior expectations indicated that perceptual noise may lead to psychotic-like experiences.
These findings suggest a model for understanding how altered perceptions may develop in susceptible individuals.

Simplified

Serotonergic psychedelics (SP) are increasingly used in clinical research and naturalistic settings, but their psychotic-like side effects, including persisting perceptual abnormalities (PPAs), are poorly understood. Psychosis-associated hallucinations are associated with susceptibility to conditioned hallucinations and computationally-estimated overweighting of perceptual expectations, or priors. However, SPs are widely argued to reduce prior weighting. We surveyed 186 naturalistic SP users on prior SP use, SP-associated PPA history, and current PPAs. Participants completed the visual conditioned hallucinations (VCH) task, in which conditioning induces perception of absent stimuli. Behavioral data were used to fit parameters of a computational model to estimate latent states driving percepts and responses. Past and current PPAs were associated with younger age at first use and higher SP doses, lower visual thresholds, higher VCH rate and confidence, and reduced sensory discrimination. Among model parameters, however, only reduced decision precision tracked both measures and mediated the dose-PPA relationship; relative prior weighting rose equivocally, as expected when priors and sensory evidence gain precision together. SP-related PPAs may therefore arise from a noisy visual system biased toward detection, in which priors act as templates that convert sensory noise into expected percepts. These findings may point to a tractable model for how psychotic-like perception emerges.

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Ongoing unusual perceptions in psychedelic users are linked to learned hallucinations and weaker sensory processing

Abstract

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