LSD microdoses subtly alter visual perception but do not change contrast surround suppression, unlike higher-dose psilocybin

A randomized, double-blind, placebo-controlled crossover study of 31 healthy adults found that 10 and 20 micrograms of LSD produced modest subjective changes in vision, including greater blurriness, color saturation, and a more dynamic appearance. However, neither dose changed performance on a visual contrast task measuring surround suppression, an illusion in which a striped pattern appears lower in contrast when surrounded by a bold pattern. The objective result contrasts with small human studies suggesting that higher doses of psilocybin can strengthen related visual illusions. The study included only 68 analyzable sessions from 24 participants, tested participants four hours after dosing, and exploratory subjective ratings may have been influenced by expectations. The findings suggest that low-dose LSD can alter conscious visual experience without measurably changing early automatic processing of visual context.