This cross-species experimental study (n=21 humans; n=10 rats) finds that psilocin (18.2mg/70kg for humans; 0.3mg/kg for rats) impairs the ability to distinguish between static and moving images in both humans and rats. In humans, the impairment aligns with psilocin plasma levels and self-reported hallucination intensity. In rats, the effect is specific to motion perception, providing the first evidence of psilocin-induced visual distortions across species.
Papers cited by this study that are also in Blossom
Tylš, F., Páleníček, T., Horacek, J. · European Neuropsychopharmacology (2013)
Background
Psychedelics, particularly psilocin, are increasingly being studied for their mind-altering effects and potential therapeutic applications in psychiatry. Visual hallucinations, especially the illusion of motion in static images, are a hallmark of their action. Despite growing interest, the underlying mechanisms remain poorly understood, as their systematic evaluation in both humans and animals is challenging.
Methods
To investigate psilocin-induced visual distortions, we designed a 2-choice visual discrimination task. Human participants and male rats indicated whether an image appeared static or moving while the image either actually moved or did not. In humans, performance was compared with self-reported hallucination intensity, Altered States of Consciousness scale scores, and psilocin plasma levels. Rats were tested in 2 distinct tasks, a luminance-based task and a motion-based task. Their performance was evaluated alongside decision time.
Results
Both species exhibited significant impairment in distinguishing static from dynamic visual stimuli while under psilocin’s influence. In humans, this impairment followed the time course of psilocin plasma levels and hallucination intensity. In rats, psilocin selectively impaired performance in the motion-based task, while performance in the luminance-based task remained intact, indicating a specific effect on visual perception. Decision time was linked to discrimination impairment.
Conclusions
Psilocin impaired static-dynamic discrimination in both species, providing the first evidence that rats experience visual distortions similar to those reported by humans. The correlations between discrimination impairment, psilocin levels, and hallucination intensity in humans reinforce psilocin’s effects on visual perception. This approach provides a valuable tool for investigating the neurobiology of altered visual perception in drug-induced states and psychiatric conditions.
Vejmola and colleagues situate their study within evidence that psychedelics, particularly psilocybin/psilocin, produce visual hallucinations and distortions such as apparent motion, contour undulation and geometric transformations. They note that 5-HT2A receptor agonism is central to these effects, that these receptors are abundant in visual pathways, and that altered 5-HT2A signalling has been implicated in visual hallucinations in clinical conditions such as Parkinson's disease and schizophrenia. Prior animal observations (disorganised behaviour, abnormal tracking or reaching at nonexistent objects across species) suggest cross-species effects, but until now no systematic, objective measurement of psychedelic-induced visual distortions in animals has been reported. To address this gap, the investigators developed a 2-choice visual discrimination paradigm applied in parallel to humans and rats. They hypothesised that psilocin would impair the capacity to distinguish static from dynamic images, yielding a tendency to misclassify static stimuli as moving. In humans, the design linked behavioural performance to self-reported hallucination intensity and plasma psilocin; in rats, decision time was used as an additional objective marker. The study aimed to provide the first objective, cross-species comparison of drug-induced apparent motion and to establish a preclinical model for studying the neurobiology of visual hallucinations.
Human experiment: The clinical component was embedded in a double-blind, placebo-controlled, crossover trial approved by local ethics bodies. Twenty-one healthy volunteers (10 women), aged 28–53 years (mean 37 ± 6.1), gave informed consent; psilocybin was administered orally at 0.26 mg/kg (capsules) and matched placebo capsules were used. The minimum washout was 28 days (mean 49 days). Participants performed a 6-minute visual discrimination task at 65, 165 and 265 minutes after ingestion, deciding whether 8-second grayscale stimuli (human faces or an ellipsoid) were "moving" or "not moving"; dynamic stimuli were created by applying visual effects while keeping luminance constant. Self-reported effects were measured retrospectively at 380 minutes using the Altered States of Consciousness (ASC) scale, and participants also provided a continuous time-course of hallucination intensity (0–7 hours). Blood samples for psilocin quantification were drawn at 1, 2, 4, 6 and 24 hours and analysed by liquid chromatography–tandem mass spectrometry; detailed pharmacokinetic procedures are reported in the supplement. Rat experiment: Ten male Long–Evans rats were housed under standard conditions and food restricted to maintain motivation. Psilocin (0.3 mg/kg) or saline was administered subcutaneously (2 mL/kg) 30 minutes prior to testing. Rats were trained in a PVC maze on a 2-choice visual discrimination protocol that progressed from a luminance-based task to a motion-based task. Static cues were vertical square-wave gratings; dynamic cues used six different smooth visual-effect distortions that preserved average luminance. Training continued until rats achieved an 85% accuracy threshold over three consecutive sessions. Testing used a 3-day protocol: baseline (training then testing), saline day, and psilocin day, with incorrect responses rewarded during testing to avoid discouraging animals and to ensure impairments reflect perceptual changes rather than motivational decline. A posttreatment training session checked retention; after a one-week washout, rats were retrained on the luminance task and retested. Data analysis: For both species, the primary behavioural metric was the correct ratio (proportion of correct trials per session). Discrimination impairment was operationalised as the absolute difference in correct ratios between placebo/saline and psilocybin/psilocin conditions. In rats, decision time (time spent in a predefined decision area) was extracted from overhead video using EthoVision Pro (version not fully reported). Areas under the curve (AUCs) for hallucination intensity and serum psilocin were computed; summary statistics included mean ± SEM or median (Q1/Q3) as appropriate. The supplement is cited for the full statistical protocol; the main text reports Wilcoxon tests, Friedman's ANOVA and paired t-tests for key comparisons.
In both humans and rats, the correct ratio was calculated as the proportion of correctly solved trials per session. Discrimination impairment was quantified as the absolute difference in correct ratios between the placebo/saline and psilocybin/psilocin conditions, as shown in the graphs. In rats, decision time-the time spent in a predefined decision area per trial (Figure)-was extracted from above-view video recordings using EthoVision Pro v. ). Data were presented as mean 6 SEM or median (Q1/Q3) where appropriate. Areas under the curve (AUCs) for self-reported hallucination intensity and serum levels were calculated using GraphPad Prism 8.0, which was also used for graph generation. For a full description of the statistical procedures, see the Supplement.
Psychedelics are known to induce the illusion of motion in static objects and textures. In this study, we examined whether this effect occurs in both humans and rats following psilocin administration. Our findings indicate that both species experience motion-like distortions to a significant degree. In humans, discrimination between static and dynamic cues remained impaired throughout the session but gradually diminished over time. High misclassification rates for static stimuli suggest that volunteers frequently perceived them as moving. This impairment closely paralleled psilocin plasma levels and self-reported hallucination intensity, with a significant correlation being observed between drug concentration and hallucinatory effects. Similarly, Madsen et al.reported correlations between plasma psilocin levels, 5-HT 2A receptor occupancy, and subjective psychedelic intensity. Discrimination impairment was also linked to OSE and VUS-scales that measure visual alterations and mystical experiences. Notably, human faces were more likely to induce apparent motion than simple ellipsoids, suggesting that the complexity of visual stimuli modulates the extent of perceived distortions. A review by Studerus et al.
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Papers in Blossom that reference this study
Scholle, P., Wenke, Š., Nekovářová, T. et al. · Journal of Psychopharmacology (2026)
Human results: Fifteen participants completed all three measurements and were included in the behavioural analyses; six were excluded because they could not perform the task during peak drug effect. Overall accuracy differed markedly between placebo and psilocybin sessions (Wilcoxon signed-rank, n = 15, W = 0, z = 3.408, p < .001). Mean correct ratios were 98.7 ± 2.0% under placebo and 76.0 ± 10.8% under psilocybin. Discrimination impairment varied with cue type and time (Friedman's ANOVA χ2(2) = 14.550, p < .001), with the largest deficit at 65 minutes post‑ingestion. At 65 minutes participants significantly misclassified static stimuli as dynamic (Wilcoxon, n = 15, W = 1, z = 3.350, p < .001); facial stimuli produced a stronger effect than ellipsoids (Wilcoxon, n = 15, W = 0, z = 2.934, p < .010). Discrimination impairment at the 65-minute point correlated with ASC subscales for oceanic boundlessness (OSE, r = 0.652, p < .05) and visionary restructuralization (VUS, r = 0.623, p < .05), and with measured psilocin serum levels (r = 0.585, p < .05). The AUC of fitted psilocin levels correlated with retrospective hallucination intensity (r = 0.547, p < .05). Psilocybin markedly increased ASC scores versus placebo across subscales (Bonferroni-corrected p < .001): OSE rose from 2.5 ± 0.4% to 60.6 ± 3.3%, AIA from 1.1 ± 0.3% to 30.3 ± 2.0%, VUS from 2.2 ± 0.4% to 64.7 ± 2.7%, and the global G‑ASC from 2.0 ± 0.4% to 50.6 ± 3.0%. Rat results: Six rats were reported as tested in both tasks (the Methods note ten animals were housed; the extracted text does not clearly reconcile this difference). Across the sample, correct ratios were significantly lower after psilocin than after saline (paired t-test, t11 = 4.693, p < .001), with mean accuracy 93.3 ± 5.7% for saline and 72.7 ± 1.8% for psilocin. Decision time was inversely correlated with correct ratio (Pearson r = -0.440, p < .05), indicating faster choices were associated with greater impairment. Discrimination impairment was larger in the motion-based task than in the luminance-based task (paired t-test, t5 = 4.067, p < .001). The authors further report that particular visual-effect manipulations (wavewarp, ripple, fisheye) produced the highest error rates, and that rats tended to perform faster and with higher accuracy on the luminance task, consistent with greater intrinsic difficulty of the motion-based discrimination.
The investigators interpret their findings as cross-species evidence that psilocin induces apparent-motion visual distortions. In humans, impaired discrimination between static and dynamic images peaked early (around 65 minutes), closely tracking psilocin plasma levels and self-reported hallucination intensity; volunteers more often perceived static stimuli as moving, and complex stimuli (faces) were particularly prone to apparent motion. The rat data showed a selective deficit in the motion-based task while luminance discrimination remained largely intact, supporting a perceptual rather than global motivational or cognitive explanation. An inverse relation between decision time and accuracy in rats suggested that rapid decisions under psilocin reflected misperception rather than careful discrimination. The authors place these results alongside prior human and animal literature, noting consistency with pharmacokinetic correlations reported elsewhere and with demonstrations that psychedelics can differentially affect aspects of motion processing. They argue that the rodent visual system's organisation into clusters analogous to primate ventral and dorsal streams makes rats a viable model for mechanistic work, including mapping stimulus propagation through the visual pathway to localise where distortions emerge. Several limitations are acknowledged. The tasks probed apparent motion but did not capture other common psychedelic visual alterations such as colour and pattern changes. Small sample size in rats and reliance on correct ratios and decision times may have limited sensitivity to subtle perceptual changes. In humans, excluding six participants who could not complete the task at peak effects could bias results toward those with less severe intoxication. Dose-equivalency across species remains challenging; the authors note previous reports of locomotor disruption at higher rodent doses and defend their choice of 0.3 mg/kg as producing perceptual effects without gross motor impairment. They recommend further studies with broader stimulus sets, larger samples, and real-time neural measurements to clarify mechanisms and locus of disruption in the visual pathway.
Vejmola and colleagues conclude that psilocin impairs static–dynamic visual discrimination in both humans and rats, and that rats exhibit motion-like visual distortions comparable in nature to those reported by humans. The human behavioural impairment correlated with psilocin plasma levels and subjective hallucination intensity. Establishing an objective, cross-species behavioural paradigm provides a preclinical platform to investigate the neurobiology of visual hallucinations and may aid development of interventions for disorders in which visual hallucinations are prevalent.