Jorge Ferrer, Ph. D. - This presentation discusses the challenge of shared psychedelic visions for scientific materialism and naturalism. Modern scholarship on hallucinations holds that the “shareable” nature of sensory claims is what distinguishes successful perception from hallucination. Whereas mainstream science dismisses psychedelicinneror individual visions as subjective brain hallucinations,how to explainshared outer visions in which several practitioners see,with their open eyes,the same subtle phenomena in the external world? Interestingly, indigenous people widely claim that visionary medicines allow access to an enhanced sensory faculty granting direct perception of subtle energies and spiritual entities—called, for example, “true seeing” by the Matsigenka of Southern Peru, “second sight” by the Thonga of Mozambique, or “stargazing” by the Navajo.After illustrating this phenomenon with cases from ayahuasca and San Pedro (wachuma) visionary events and documented anthropological evidence, a case is made that standard“collective” or “public hallucination” models fail to account for these phenomena. The presentation concludes that shared psychedelic visions not only present a serious challenge to scientific naturalism and materialism, but also suggest the existence of subtleworlds or dimensions of reality coexisting with the physical domain.These phenomena also raise the possibility of intersubjective testing of so-called supernatural claims through a radical empiricist epistemology (after James) that challenges the scientist attachment of “empirical validity” to “naturalistic sensory evidence.”Finally, a participatory research program is outlined that bridges the naturalistic/supernaturalistic split by embracing a more liberal or open naturalism—one that is receptive to both the ontological integrity of spiritual referents and the plausibility a multiverse or multidimensional cosmos housing a rich varietyof subtle worlds.