What phenomenon occurs when hallucinogens interfere with neurotransmitters, leading to a mixing of the senses?

The phenomenon described is synesthesia, which occurs when stimulation of one sensory pathway leads to automatic, involuntary experiences in a second sensory pathway. This means that individuals may "see" sounds or "taste" colors, blurring the lines between different sensory modalities.

In the context of hallucinogens, these substances can disrupt the normal processing of sensory information by interfering with neurotransmitters, particularly serotonin. This interference can lead to the experience of synesthesia, where users report mixed sensory experiences. Hallucinogenic drugs like LSD or psilocybin are known to induce such experiences, causing users to perceive the world in unique and often profoundly altered ways.

The other options do not accurately describe this phenomenon: illusions are distortions of real sensory perceptions, delusions are erroneous beliefs not grounded in reality, and altered reality refers more generally to a change in perception without the specific sensory mixing characteristic of synesthesia. Hence, synesthesia is the correct term that specifically identifies the mingling of senses resulting from hallucinogen use.