Abstract
Psilocybin alters perception and brain dynamics. Here, we investigate the effects of psilocybin using psychophysics, ultra-high field functional MRI, and computational modeling. We find that psilocybin alters contextual perception in the Ebbinghaus illusion, as well as contextual modulation in cortical responses to visual stimuli. We propose a computational model capable of capturing and linking these changes. Leveraging vision as a beachhead, our findings highlight the alteration of contextual computations as a potential general mechanism underlying psychedelic action.