Effects of ayahuasca on binocular rivalry with dichoptic stimulus alternation

Binocular rivalry occurs when each eye is shown a different image, and the brain alternates which one is consciously perceived. A variant called dichoptic stimulus alternation (DSA) rapidly swaps the images between eyes, typically disrupting rivalry. This study tested whether the psychedelic brew ayahuasca alters this effect. Ten volunteers performed binocular rivalry tests at DSA rates of 0, 3.75, 7.5, 15, and 30 Hz before and after drinking ayahuasca. After ingestion, mean dominance periods—the time one image is perceived—increased under standard conditions and at all DSA rates. At the highest rates (15 and 30 Hz), dominance periods were longer on ayahuasca, suggesting the brew helps maintain rivalry where it would normally break down, possibly due to slowed visual processing and altered gamma oscillations.

Study at a glance

Abstract

RationaleDuring 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.ObjectiveThe study was undertaken to investigate whether binocular rivalry survives high rates of DSA induced by the South American hallucinogenic beverage ayahuasca.MethodsTen 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.ResultsIngestion of ayahuasca increased mean dominance periods both in standard binocular rivalry conditions (no DSA) and tests with DSA. At higher DSA rates (15 and 30 Hz) the total length of dominance periods was longer on the brew.ConclusionIt is discussed that ayahuasca-induced survival of binocular rivalry at high DSA rates may be related to slow visual processing and increased mean dominance periods may result from hallucinogen-induced alteration of gamma oscillations in the visual pathways.