Psychopharmacology © Springer-Verlag 2003 DOI 10.1007/s00213-003-1701-x Original Investigation Effects of ayahuasca on binocular rivalry with dichoptic stimulus alternation E. Frecska (✉) · K. D. White · L. E. Luna E. Frecska · L. E. Luna Wasiwaska Research Center, Florianópolis, SC, Brazil K. D. White Department of Psychology, University of Florida, Gainesville, Fla., USA L. E. Luna Swedish School of Economics, Helsinki, Finland E. Frecska MHC, Napvirág u. 19, 1025 Budapest II, Hungary ✉ E. Frecska Phone: +36-1-3944388 E-mail: efrecska@hotmail.com Received: 28 May 2003 / Accepted: 30 October 2003 Abstract Rationale During binocular rivalry, two incompatible images are presented to each eye and these monocular stimuli compete for perceptual dominance, with one pattern temporarily suppressed from awareness. One variant of stimulus presentation in binocular rivalry experiments is dichoptic stimulus alternation (DSA), when stimuli are applied to the eyes in rapid reversals. There is preliminary report that in contrast with healthy controls, schizophrenic patients can maintain binocular rivalry even at very high DSA rates. Objective The study was undertaken to investigate whether binocular rivalry survives high rates of DSA induced by the South American hallucinogenic beverage ayahuasca. Methods Ten individuals who were participating in ayahuasca ceremonials were requested to volunteer for binocular rivalry tests (DSA=0, 3.75, 7.5, 15 and 30 Hz) without and after drinking the brew. 1