Objective

Psychosis-like perceptual distortions can occur in the general population, and both stress and caffeine can enhance the proneness to psychosis-like experiences, such as hallucinations. The current study aims to explore the effects of acute caffeine intake and acute stress on perceptual distortions in a double-blind, placebo-controlled experiment.

Methods

Regular caffeine consumers (n = 92) and non/low consumers (n = 89) were assigned to 100 mg caffeine/placebo and stress/no stress conditions. The White Christmas Paradigm (WCP) was used to measure hallucination-like symptoms, and bias towards threat-related words was used as an indicator of persecutory ideation. Participants reported their daily caffeine intake, and completed the State-Trait Anxiety Inventory, the Launay-Slade Hallucination Scale, the Persecutory Ideation Questionnaire and the Marlow-Crowne Social Desirability Scale.

Results

Acute stress slightly increased hallucination-like experiences, but not recall bias, while the small amount of caffeine had a time-dependent effect on recall bias. Proneness to persecutory ideation was positively and social desirability was negatively correlated with recall bias towards threat-related words, while proneness to hallucinations positively correlated with hallucination-like experiences.

Conclusions

Our results indicate that psychosocial stress—in line with the diathesis–stress model—can lead to the enhancement of hallucination-like experiences.