Effect of mescaline, lysergic acid diethylamide and psilocybin on color perception

Summary

Twenty subjects were given three psychotomimetic drugs (mescaline, LSD-25 and psilocybin) in fixed doses, 18 receiving all three. Color experience was tested by applying stimuli involving color perception, stimuli eliciting subjective colors, and stimuli usually devoid of visual experience.

Almost all measures of color perception were affected. Hue discrimination was decreased significantly by psilocybin, to a slightly lesser extent by the other two drugs. Color reports in after-images were significantly increased by all three drugs, but duration of after-image was increased significantly only by psilocybin. Elicitation of subjective colors from flicker was increased by all three drugs, significantly more by mescaline and LSD-25 than by psilocybin. The combination of flicker and pure tones evoked more color reports than flicker alone. The increase was significant only after LSD-25, no significant differences being demonstrated between the effects of the three drugs. Visual effects, both colors and patterns, elicited by pure tones were significantly increased by LSD and mescaline, though these effects were not great at the doses used in this study. Spectral patterns of evoked colors varied slightly between the three drugs.

These results are interpreted as indicating that stimuli which evoke subjective color phenomena, or even those not usually associated with visual phenomena, are enhanced by psychotomimetics. On the other hand, the usual perception of color, as judged by hue discrimination, may actually be slightly decreased.