>(in caves for 48 hrs)

!! Stroll on Mr B...

You got me thinking too, the thing that niggles at the back of my head about the pharacological argument for CnR entoptics is the commonality of the design across the globe. There just ain't a plant/naturally occurring psychedelic that exists all over the world. Nor (that I can think of) is there even an active ingredient that would be present in enough plants to account for concentrics and spirals. The only common factor is the structure of retinal processing networks. I've studied them in tedious detail, and they do contain and spot for, dots with concentric rings around them. But how the heck do you get them to announce themselves clearly to the visual cortex? Usually they are subsumed by other networks between the visual cortex and the association cortex (where the patterns ofnerve impulses are put together into an image).

The only candidate I can think of would be a drug which dampened down 5HT transmission, like psilocybin, but whilst it occurs all over the place, as you rightly point out psilocybin doesn't seem to kick out images of concentrics.

I'm currently wondering if (in a way related to stuff on another thread here at the mo, nature/nurture debate stuff) because our modern brains develop in a world full of 'un-natural' visual stimulus (perfect circles, triangles, straight lines etc), as we grow through childhood, our visual cortex develops differently from the way in which that of prehistoric people's did.

It's good to ponder.

PS: What *is* that mental looking thing you have as your avatar?