Ah, but the eyes being concentrics is part of the thing is it not? It wouldn't have been possible (imho) for Brown to have pulled that trick if he'd chosen something less deeply embedded into our visual hardwiring. And that's what makes it interesting to me, as it suggests (to my mind anyway) that the CnR carvers somehow recognised that these images were one of the basic elements of vision. Similar with the chevrons, lozenges etc, as steted by the old migraneur-hallucination theory of RA entoptic epidemiology, rather than the 3 stages of trance version.

In short, I am now tempted to embark on a campaign to prove that the ancients understood neurology to a functional cellular level, and that the Men-an-Tol is in fact a prehistoric fMRI scanner ;)