In brief
- A double-blind, placebo-controlled crossover trial tested 10 and 20 µg of LSD against a visual contrast illusion.
- The illusion remained unchanged at both doses, even though participants reported blurred vision, increased color saturation, and a more dynamic visual field.
- The authors interpret this as a dissociation between subjective experience and early visual processing, and call for testing higher doses.
One of the open questions regarding psychedelics is exactly what happens to perception when taking very low doses. A team from the University of Basel has tested a classic optical illusion with LSD microdoses, and the result is more nuanced than one might expect: people report seeing things differently, but objective testing shows no change.
The illusion tested
The study, published in the journal Neuroscience of Consciousness and authored by Lucca F. Jaeckel, Philipp Sterzer, Matthias E. Liechti, and colleagues, utilized what is known as surround contrast suppression. This is an illusion where a patch of stripes is perceived as having less contrast if it is surrounded by a high-contrast ring. It had previously been established that this type of illusion is strengthened by psilocybin at moderate or high doses. It remained to be seen whether low-dose LSD would have a similar effect.
The design was randomized, double-blind, placebo-controlled, and crossover: each volunteer underwent three sessions separated by at least one week, receiving a placebo, 10 µg of LSD, or 20 µg of LSD. The task was performed four hours after administration. In each of the 100 trials per session, the participant viewed two patches of moving stripes for one second—one surrounded by the ring and one not—and had to identify which had higher contrast.
What was measured and the results
Approximately 30 healthy adults participated, with an average age of about 28, and half had used psychedelics previously. Of 93 completed sessions, only 68 (from 24 individuals) met the quality criteria, primarily because the task was either misunderstood or could not be completed in the discarded cases.
The illusion appeared reliably, but LSD did not modify its strength at either dose. Statistical analysis weighed the evidence for and against an effect and leaned clearly toward the absence of an effect.
Subjective experience was a different story, although this part was exploratory and not preregistered. At 20 µg, the overall sense of effect increased by about 17 points out of 100, and visual changes emerged: colors appeared more saturated, the world seemed more dynamic, and vision was blurrier. At 10 µg, only slightly blurrier vision was noted compared to the placebo. These changes were minor and did not correlate with individual performance on the contrast task. The study reported no adverse effects.
Implications
The authors themselves point out several limitations. At 20 µg, participants distinguished LSD from the placebo better than chance, meaning the blinding was partial, which may have inflated subjective ratings—though they maintain that expectation alone is unlikely to explain the results. The dose may have been too low to affect early visual processing: they cite a comparison suggesting that 20 µg of LSD is roughly equivalent to 4 mg of psilocybin, compared to the 25 mg used in the previous psilocybin study. Furthermore, the test was conducted four hours after administration, past the peak, and participants were asked to abstain from caffeine, which could have affected the concentration of regular users. They also propose, as an unproven hypothesis, that LSD’s effects on dopamine—which psilocybin lacks—might compensate for a potential change.
The cautious conclusion is that alterations to this visual mechanism do not appear necessary for the perceptual effects of a microdose to occur. This says nothing about higher doses or other functions. For those looking to contextualize these findings, the Psychedelics Guide compiles what is known and what is not, and the page on LSD and ergot covers its history and pharmacology. Liechti declares that he is a consultant for Mind Medicine and Lykos Therapeutics.
Source
- PsyPost. Psilocybin appears to strengthen this optical illusion, but LSD microdoses do not, regarding Jaeckel et al., “Low-dose lysergic acid diethylamide alters subjective visual perception but not visual contrast surround suppression,” Neuroscience of Consciousness (DOI 10.1093/nc/niag050). PsyPost, October 15, 2026.
Educational content written from a harm reduction perspective and with respect for individual freedom. It is not a substitute for advice from a healthcare professional and is not intended to encourage or condemn any drug use.
