Theoretical Background and Rationale: Serotonergic psychedelics are remarkable for their capacity to induce variable yet reproducible modifications to human consciousness. The most salient acute effects of these compounds include perceptual alterations, predominantly in the visual domain, yet to date these alterations have been mostly documented only by subjective reports.

Research Question and Hypothesis: This double-blind placebo-controlled study under semi-naturalistic conditions explores psilocybin's effect on visual perception and ocular dynamics. Framed within the context of the entropic brain theory, we hypothesized that visual spatial exploration would manifest as less concentrated and more uniform, yielding an increase in the entropy of the fixation probability distribution.

Methods and Analysis: Using an eye tracker, gaze fixations were recorded as participants freely explored artworks on a screen under the effects of psilocybin. Participants also provided self-assessments of emotional and aesthetic aspects for each artwork, along with a questionnaire covering aspects of the aesthetic experience

Main Findings: we demonstrated that high doses of psilocybin result in a more local visual exploration, and thus in a less entropic fixation probability distribution. Participants reported heightened emotional response and state of flow under the high dose condition.

Conclusion: These findings are consistent with an effect of psilocybin on gaze fixation mediated by altered perception of low-level visual information, such as textures, shapes and colors. Our work also highlights the possibility of investigating psychedelics by addressing their effect on behavior under complex naturalistic conditions, which contributes to maintaining subject engagement while also increasing the ecological validity of the findings.