Enhanced visual contrast suppression during peak psilocybin effects: A psychophysical study

Surround suppression, a visual effect where a central stimulus appears less contrasty when placed inside a higher-contrast surround, is altered by the psychedelic compound psilocybin. In a small experiment with six participants, a 25 mg dose of psilocybin produced stronger surround suppression of perceived contrast compared to a placebo (100 mg niacin). The intensity of subjective psychedelic visuals correlated positively with the magnitude of surround suppression. This finding may be relevant to understanding visual effects of psilocybin and its therapeutic mechanisms, given that weakened surround suppression has been observed in major depressive disorder, for which psilocybin is considered a breakthrough therapy.

Study at a glance

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.