Our ability to perceive the world around us depends on functioning sensory cells sending information to our brains. Exemplified by how a blind person from birth wonders what a sighted person sees, or a deaf person muses about what hearing people hear, our constructed reality is limited by what types of sensory input we’re used to.

All of this goes out the window, however, when humans take hallucinogenic drugs.

Mescaline, psilocybin mushrooms, and LSD, in particular, are known to induce a temporary sensory crossover, known as acquired synesthesia, wherein the tripper simultaneously experiences heightened phenomena in more than one sensory pathway. Most commonly, users have bizarre overlaps in audio-visual perception – for example, a song playing on the radio “sounds” like purple – though examples of taste and smell joining the psychedelic party have also been reported in scientific literature.

But until now, one unique situation had never been investigated: How would a blind person hallucinate on drugs closely associated with visual disturbances? Thanks to an amazingly entertaining case study by University of Bath psychologists, published in Consciousness and Cognition, we now have a little insight.

Their report is based on the experiences of a 70-year-old male, referred to as Mr Blue Pentagon (BP), who was blind from birth. A man of the times, BP took a lot of drugs during his heyday as a rock musician in the 1970s and early 1980s.

Throughout his many trips, BP experienced temporary synesthesia, temporary loss of his ability to speak or understand language, and distortions of time perception, yet he never formed any mental images.

“Every time I did acid, I experienced something new and spectacular,” he recounted to the researchers. “Obviously through the senses which are available to me! I never had any visual images come to me. I can’t see or imagine what light or dark might look like.”

When describing his most potent cross-sensory experience, BP recalled how listening to Bach's third Brandenburg concerto made him feel like he “was immersed in the most beautiful waterfall ever.”