MonoMonday: Optical Illusion - "Mono...or is it?"

Marlieske has excelled herself with this really fun MM challenge of "Optical Illusion" this week.

You'll see that my title is "Mono...or is it?"! Well of course it is, if you just look at it normally. My "Editor" was very good about sitting for her portrait when she knew I was going to turn her into a negative (rest assured, it wasn't the Daleks trying to exterminate her...).

BUT - if you stare at the tip of her nose for 30 seconds, then turn your eyes quickly to look at a reasonably bright plain wall or similar, and blink fast several times, you'll see a positive image in faint colours! It works best if you view the negative photo LARGE on a PC or big tablet, as the black background you get with that helps the illusion. But it also works even on a phone if you hold it pretty close while you stare at it (use reading specs if necessary!).

I confess that I got the idea from the web and I'm pondering how it works. After-images like this are caused by "persistence of vision": the light-sensitive pigment in some of the photoreceptors in the retina (where the light has shone more brightly) become temporarily more bleached than the others, , so that when you look away the unbleached receptors are, for a moment, more senstive to light than the others. I assume that in this example the receptors for some colours are more susceptible to bleaching than for other colours, resulting in the colour effect. Whether I'm right or not, it's fascinating.