Enhanced visual contrast suppression during peak psilocybin effects: Psychophysical results from a pilot randomized controlled trial
Journal of Vision – November 05, 2024
Source: OpenAlex
Summary
Psilocybin profoundly alters visual perception, strengthening an effect called surround suppression where a high-contrast background reduces a central image's apparent contrast. A randomized controlled trial with 6 participants found a 25 mg psilocybin dose significantly increased this visual suppression compared to placebo. This finding, relevant to psychology and medicine, illuminates psilocybin's impact on sensory processing. The intensity of subjective psychedelic visuals correlated with this effect, offering insights for Psychedelics and Drug Studies into altered perception—relevant from audiology to paranormal experiences and beliefs—and informing complementary and alternative medicine.
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). 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.