Binocular rivalry, where each eye sees a different image and perception alternates between them, was slowed by psilocybin (215 µg/kg) in ten healthy adults. Pretreatment with ketanserin (50 mg), a 5-HT2A receptor blocker, prevented most of psilocybin's hallucinogenic symptoms but did not reverse the slowing of rivalry switching or the drug's negative-type symptoms such as reduced arousal and vigilance. These findings link slower binocular rivalry switching to subjective levels of arousal and attention, and suggest that psilocybin's effect on rivalry is not mediated by the 5-HT2A receptor.
Binocular rivalry, where each eye sees a different image and perception alternates between them, is influenced by psilocybin. In 12 healthy volunteers, both low (115 µg/kg) and high (250 µg/kg) doses of psilocybin significantly reduced the rate and rhythmicity of perceptual alternations 90 minutes after administration, compared to placebo. Over time, switch rates increased, with some exceeding pretest levels at 360 minutes, though mean phase duration did not significantly differ from placebo. Drug-induced changes in rivalry phase durations corresponded to altered states of consciousness measured by the 5D-ASC scale. The findings implicate serotonergic pathways and support a brainstem oscillator's role in perceptual rivalry and psychosis symptoms.