In an article I wrote for a newsletter a year or two ago, I mentioned the concentric circles I often see in the grass when my sight is easy and relaxed. I read an article the other day that may go some way to explaining the phenomenon. In her article, Uncoiling the spiral: Maths and hallucinations, Marianne Freiberger explains the strange convergence of mathematics, hallucinations and neurocognitive science. It even includes material about how Alan Turing, the great computer pioneer, hypothesized about the role of mathematics in the stripes on zebras. I find it all fascinating.

link to article