A Basel-led study on very low doses of LSD has found that while participants reported perceptual changes such as colours appearing more saturated and the world seeming blurrier and more dynamic, the drug did not measurably alter the visual contrast surround suppression illusion that underpins how the surrounding scene affects perception. The research was published in Neuroscience of Consciousness.
Surround suppression is a well-known feature of the visual cortex, where the brain’s processing of a central pattern is influenced by the surrounding visual context. A classic example is that a striped centre looks fainter when surrounded by a bold, high-contrast ring, a phenomenon researchers believe arises in part from activity in neurons that dampen responses to the centre.
Psychedelics are thought to exert much of their effect by activating a serotonin receptor on brain cells. A large analysis of more than 6,000 written accounts of psychedelic trips, previously covered by PsyPost, linked reports of altered sensory perception to areas of the visual cortex rich in serotonin receptors.
Animal work has also hinted that psychedelics can shift how much the brain relies on visual context. For instance, a 2019 mouse study showed a psychedelic drug reducing surround suppression in the visual cortex, a finding that suggested a potential direction for how perception might be altered.
In humans, the pattern may diverge. A small 2024 pilot study found that a high dose of psilocybin heightened the contrast illusion, and that individuals experiencing stronger visual effects tended to show bigger neural changes. A 2025 study extended this to show that low to moderate doses of psilocybin increased susceptibility to the Ebbinghaus illusion, indicating that psychedelics can alter how the brain uses surrounding visual context.
Meanwhile, some people pursue microdosing—very small amounts of psychedelics—in the belief that mood or creativity might receive a boost. A separate study in 2022 reported that repeated LSD microdoses did not reliably improve mood or cognitive performance compared with a placebo, though higher doses produced small increases in vigor. The new study set out to test whether those very small doses could also affect basic visual perception.
The research was led by Lucca Jaeckel, a doctoral student at the Translational Psychiatry Lab within the University of Basel’s Department of Psychiatry. He explained that several theories attempt to account for how psychedelic drugs alter visual perception.
“There are different theories about how psychedelic drugs cause altered visual perception,” Jaeckel told PsyPost. “A few studies, two of which investigated psilocybin in humans, have shown alterations in a neural phenomenon called surround suppression, where brain responses to a stimulus at some location in the visual field are suppressed by stimulation in the surrounding area.”
“We wanted to see if LSD microdoses (10 and 20 μg) affect these processes in the same way as psilocybin, using a contrast discrimination task in healthy human participants,” Jaeckel said.
The study employed a randomised, double-blind, placebo-controlled crossover design with 31 healthy adults who completed at least two sessions. Each participant underwent three testing days at least a week apart, receiving a placebo on one day, 10 micrograms of LSD on another, and 20 micrograms on the third. Neither the participants nor the researchers knew which substance was administered on any given day until after the study concluded. Participants averaged 28 years old, and about half had prior psychedelic experience.
Four hours after dosing, participants completed a visual contrast task consisting of 100 trials. In each trial, they viewed two circular patches of drifting light and dark stripes; one patch sat at the centre inside a ring of high-contrast stripes, while the other appeared off to the side with no ring. They pressed a key to indicate which patch looked higher in contrast. The surrounding ring creates a suppressing illusion, so the centre patch is typically perceived as lower in contrast.
Between tasks, participants completed extensive questionnaires rating subjective experiences on 100-point scales. They assessed whether vision seemed sharper or blurrier, brighter or darker, more or less saturated with colour, and whether it felt static or dynamic. They also rated broader experiences such as boundary dissolution or visionary changes.
On measures of subjective experience, the higher dose produced more noticeable effects. On a 100-point scale, ratings of “any drug effect” rose by about 17 points at 20 micrograms and by about 5 points at 10 micrograms. The 20-microgram dose also yielded mildly altered states of consciousness, with higher scores for visionary changes, oceanic boundlessness, and reduced alertness. These increases were small, roughly 2 to 5 per cent of the scale’s maximum.
Visually, participants reported that 20 micrograms made colours appear more saturated, the world seem more dynamic, and their vision blurrier. The 10-microgram dose also produced a slight blurring relative to placebo, though brightness did not change significantly. The shifts were modest, around 3 to 7 points on a 50-point span in either direction from “normal.”
At the end of each session, participants guessed which treatment they had received. They correctly identified the placebo and the 20-microgram dose at better-than-chance levels, but not the 10-microgram dose.
“There is considerable disagreement as to what dose of a psychedelic constitutes a microdose,” Jaeckel noted. “We used doses of 10 and 20 μg which are often considered microdoses.”
“Some people would argue a microdose is a dose that does not noticeably affect conscious state,” he explained. “Interestingly, our 10 μg dose was not identified as an active dose beyond chance level, yet we could show a small effect of that low dose on subjective visual perception.”
Yet the objective results did not mirror the subjective reports. Of 93 completed sessions, 68 from 24 participants met the researchers’ quality criteria; the remainder largely failed because participants misunderstood or could not perform the task. In the remaining data, the contrast illusion was reliably produced, but LSD did not measurably change its strength. A formal analysis weighing evidence for and against an effect strongly favoured no effect of the drug.
The researchers additionally looked for a link between subjective visual changes and objective task performance. They found no correlation between the largest subjective visual changes at 20 micrograms and larger shifts on the task, unlike the 2024 psilocybin pilot study that linked stronger visual effects with greater suppression. This suggests that, at these doses, conscious perceptual changes can occur without alterations in the brain’s early automatic processing of visual contrast.
“Unlike psilocybin, LSD did not affect spatial context-related contrast perception as would be expected from altered surround suppression. At the same time, we did find subjective alterations to visual perception,” Jaeckel said. “This indicates that alterations in surround suppression are not necessary for the perceptual alterations induced by LSD. Nevertheless, it may be that psychedelics affect surround suppression at higher doses where this may affect visual perception.”
As with any study, there are caveats. Because participants could often tell when they had received the 20-microgram dose or a placebo, expectations may have inflated their subjective ratings. The authors argue that expectations alone are unlikely to explain the visual effects, noting that some sources describe low-dose psychedelics as sharpening vision, which would contrast with the blurriness reported here.
The authors propose that the most plausible reason for the lack of an objective effect is the very low dose. On direct comparison, 20 micrograms of LSD is roughly equivalent to 4 milligrams of psilocybin—far below the 25-milligram dose used in the 2024 contrast study and slightly below the 5-milligram dose that affected the size illusion in the 2025 study.
Experts suggest that LSD may alter conscious perception through mechanisms that do not impinge on early visual processing at these levels. The authors also note that LSD interacts with dopamine receptors in ways psilocybin does not, and these effects—potentially emerging later in the drug’s time course—could counteract any effect on surround suppression.
Timing and design choices also matter. The contrast task was administered four hours after dosing, potentially past the peak of the drug’s effects, and participants were asked to avoid caffeine before and during sessions because caffeine can influence brain activity and surround suppression. For regular caffeine users, withdrawal or fatigue could have affected task focus mid-session.
Looking ahead, the researchers propose testing higher LSD doses to see whether the contrast illusion shifts at stronger levels or evaluating earlier time points in the drug’s timeline. For now, the evidence suggests that while low doses of LSD can make the world seem more colourful, blurrier and more dynamic, they did not measurably alter the brain’s processing of this particular visual context cue.
“This is the first publication from a larger study investigating how LSD affects how different kinds of context are used toward making choices about perceptual stimuli,” Jaeckel told PsyPost, indicating that more data are forthcoming.
Co-author Matthias Liechti serves as a consultant for Mind Medicine, a company developing LSD-based treatments, and Lykos Therapeutics.
The study, “Low-dose lysergic acid diethylamide alters subjective visual perception but not visual contrast surround suppression,” was conducted by Lucca F. Jaeckel, Deborah Logvinski, Mika Kanana, Felix Müller, Nicolai Rohner, Anna M. Becker, Matthias E. Liechti, and Philipp Sterzer.
