With high doses of diazepam I definitely notice this - not to a huge extent but definitely to some. I've never experienced a psychedelic trip so I can't compare, but it feels like the lights are more intense and colours appear more vivid and lovely. Morphon - maybe you're right, the eye muscles could relax to the point where it starts to happen, or it could be something to do with the GABA receptors, as lorazepam can bring on hallucinations and ambien quite vivid and disturbing ones, diazepam could affect the same receptor but to a weaker extent perhaps... Just my theory, but could be wrong. Either sounds quite probable.