Belatedly I notice that others also have posted likewise. No matter, strengthens the intent.

Great! How did you do that, with a VDU? And what was the delay between center and periphery?

ah, can't remember ever having heard about that.

One possible explanation: Flash is brighter in the center. And in the retina 10x brighter is about 14 ms faster.

that's the cow I meant.

Or Dallenbach's cow?

Are you possibly referring to Mooney Faces?

It helps if you know Objective C + Apples GUI toolbox (in fact, nearly the same). I programmed over 100 #visual phenomena ( #illusions) and a major vision test battery with it…

I wrote a program to add the page numbers to the index words (its even on GitHub), but my editor said my selection was crap ( in politer words)…
Advice I thought of too late: set up a long-lasting web page for errata and put the URL into the book.