This placebo-controlled study (n=6) investigates how psilocybin (25mg) affects visual surround suppression compared to placebo (100mg niacin). The study finds increased surround suppression effects under psilocybin, with stronger suppression correlating with more intense subjective visual effects.

Abstract of Enhanced visual contrast suppression during peak psilocybin effects

“In visual perception, an effect known as surround suppression occurs wherein the apparent contrast of a center stimulus is reduced when it is presented within a higher-contrast surrounding stimulus. Many key aspects of visual perception involve surround suppression, yet the neuromodulatory processes involved remain unclear. Psilocybin is a serotonergic psychedelic compound known for its robust effects on visual perception, particularly texture, color, object, and motion perception. We asked whether surround suppression is altered under peak effects of psilocybin. Using a contrast-matching task with different center-surround stimulus configurations, we measured surround suppression after 25 mg of psilocybin compared with placebo (100 mg niacin). Data on harms were collected, and no serious adverse events were reported. After taking psilocybin, participants (n = 6) reported stronger surround suppression of perceived contrast compared to placebo. Furthermore, we found that the intensity of subjective psychedelic visuals induced by psilocybin correlated positively with the magnitude of surround suppression. We note the potential relevance of our findings for the field of psychiatry, given that studies have demonstrated weakened visual surround suppression in both major depressive disorder and schizophrenia. Our findings are thus relevant to understanding the visual effects of psilocybin, and the potential mechanisms of visual disruption in mental health disorders.“

Authors: Link Ray Swanson, Sophia Jungers, Ranji Varghese, Kathryn R. Cullen, Michael D. Evans, Jessica L. Nielson & Michael-Paul Schallmo

Summary of Enhanced visual contrast suppression during peak psilocybin effects

The study investigates how psilocybin, a classic psychedelic that impacts serotonin receptors, alters visual perception, specifically the effect of surround suppression. Surround suppression is a phenomenon where a central image appears less contrasted when surrounded by higher-contrast visuals, a critical function for depth and object recognition. Psilocybin, known for vivid sensory effects, can also affect spatial and perceptual processes. This study builds on findings linking weaker surround suppression with certain mental health disorders like major depressive disorder (MDD) and schizophrenia, exploring whether psilocybin modulates these effects, which could have implications for psychiatric treatment.

Methods

Study Design

The research was a triple-blind, randomised, placebo-controlled trial at the University of Minnesota. Psilocybin (25 mg) was administered to healthy participants who had prior psilocybin experience but no major mental health diagnoses. Six participants completed both drug and placebo conditions, separated by a washout period.

Stimuli and Task Setup

Visual stimuli were presented on a high-definition monitor in three different configurations: No Surround (NS), Orthogonal Surround (OS), and Parallel Surround (PS). The task required participants to match contrasts between a central target and a reference stimulus, with Point of Subjective Equality (PSE) used as the measure of perceived contrast. Data was analysed through ANOVA and linear mixed-effects models.

Subjective Effects Assessment

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Find this paper

Enhanced visual contrast suppression during peak psilocybin effects: Psychophysical results from a pilot randomized controlled trial

https://doi.org/10.1167/jov.24.12.5

Open Access | Google Scholar | Backup | 🕊

Cite this paper (APA)

Swanson, L. R., Jungers, S., Varghese, R., Cullen, K. R., Evans, M. D., Nielson, J. L., & Schallmo, M. P. (2024). Enhanced visual contrast suppression during peak psilocybin effects: Psychophysical results from a pilot randomized controlled trial. Journal of Vision, 24(12), 5-5.

Study details

Compounds studied
Psilocybin

Topics studied
Healthy Subjects Neuroscience

Study characteristics
Original Placebo-Controlled Active Placebo Double-Blind Within-Subject Randomized Bio/Neuro

Participants
6 Humans

Compound Details

The psychedelics given at which dose and how many times

Psilocybin 25 mg | 1x

Linked Clinical Trial

Visual Surround Suppression and Perceptual Expectation Under Psilocybin
The prospective study will address the critical need for more precise characterizations of the acute visual effects of the drug psilocybin by measuring the impact of acute psilocybin intoxication on a perceptual task known as visual surround suppression, compared to an active placebo control.