I'm currently listening to a TM lecture that some of you may not have heard before as I've not seen it widely disseminated. It's titled, "Mushrooms, Evolution, and the Millenium" and can be found here. It's absolutely riveting and I highly recommend it. Within, he discusses his stoned ape theory which you're probably all familiar with. In brief, the theory states that the mildly hallucinogenically (sp?) affected mammal has an evolutionary advantage due to the positive benefit conferred upon its visual acuity. Where competition rules (provided you subscribe to the survival of the fittest theory) this can mean the difference between life and death.
I've only ever heard of experiments done on visual perception, though. Does anyone know if other senses are positively enhanced (not distorted) when on naturally occurring psychedelic substances and if there have been studies which bear this out?