A small experiment with six participants tested whether the psychedelic compound psilocybin alters surround suppression, a visual effect where a high-contrast background reduces the perceived contrast of a central object. After taking 25 mg of psilocybin, participants reported stronger surround suppression compared to placebo (100 mg niacin). The intensity of subjective psychedelic visuals correlated positively with the magnitude of surround suppression. No serious adverse events occurred. The findings suggest a link between serotonergic neuromodulation and visual contrast perception, and may relate to weakened surround suppression observed in major depressive disorder and schizophrenia.
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.