Enhanced visual contrast suppression during peak psilocybin effects: A psychophysical study
OpenAlex – January 11, 2024
Source: OpenAlex
Summary
Psilocybin profoundly alters visual perception, intensifying a phenomenon called surround suppression. Participants (n=6) reported stronger suppression of a visual stimulus's perceived contrast after 25mg of this hallucinogen compared to placebo. This effect, crucial for understanding visual cortex function in psychology, correlated positively with subjective 'visual hallucinations.' This suggests a neurotransmitter receptor influence on behavior. Given weakened surround suppression in major depressive disorder, these insights into psilocybin's impact on perception offer a compelling avenue for psychedelic therapies.
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.