Enhanced visual contrast suppression during peak psilocybin effects: A psychophysical study
Link Swanson, Sophia Jungers, Ranji Varghese, Kathryn R. Cullen, Michael D. Evans, Jessica L. Nielson, Michael‐paul Schallmo
January 11, 2024 preprint DOI: 10.31234/osf.io/5rm62 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Randomized controlled trial |
|---|---|
| Sample size | 6 |
| Population | Human participants |
| Interventions | Psilocybin Niacin |
| Dose | 25 mg |
| Topics | Psilocybin |
| Keywords | Visual hallucination Stimulus psychology Hallucinogen Surround suppression Visual perception Audiology Visual cortex Contrast vision Cognitive psychology Optics |
| Citations | 1 |
| Key findings | Psilocybin increased surround suppression of perceived contrast compared to placebo, and the magnitude of surround suppression correlated positively with the intensity of psychedelic visuals. |
Abstract
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). 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 impact of our findings for the field of psychiatry, given that recent studies have demonstrated weakened visual surround suppression in patients with major depressive disorder, for which psilocybin has recently been identified as a breakthrough therapy. Our finding is thus relevant to understanding the visual effects of psilocybin, and the potential mechanisms of psychedelic therapies for mental health disorders.