Psychedelic drugs and perception: a narrative review of the first era of research

A narrative review of early- to mid-20th-century research finds that psychedelic drugs alter perception across multiple sensory domains. Psychedelics influence all levels of the visual system, from retina to cortex, and can produce complex imagery and hallucinations. They also affect auditory discrimination and processing, sometimes leading to auditory hallucinations. The drugs distort body schema and time perception. Methodological limitations of that era temper the findings. The review preserves and synthesizes this pioneering work to guide future studies.

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Abstract

Abstract Psychedelic drugs are well-known for transiently altering perception, and in particular, for their visual effects. Although scientific interest into the substances’ effects on perception increased during the first era of psychedelic research during the early to mid-20th century, there is currently no source where these findings have been synthesized. In addressing this gap, the current narrative review found that psychedelics were examined for their influences across all levels of the visual system (e.g., retinal, cortical, subcortical, simple visual processing, complex imagery, hallucinations). Psychedelics were also shown to affect auditory discrimination/generalization, neural correlates of auditory processing, and led to auditory hallucinations in subsets of participants. Several studies demonstrated that psychedelics can distort representations of body schema and time perception. Concerns regarding methodological standards of this era are a limitation to the findings and are discussed. Collectively, this review preserves and increases the accessibility of the work done by pioneering psychedelic/perception researchers, synthesizes findings, and critically analyzes areas of discrepancy to inform future studies.