the eye primarily senses changes. If something isn't moving or changing on the retina, it doesn't appear. This is why you don't normally see all the blood vessels and nerve fibres in your eye (which due to a rather spectacularly bad design, actually run directly in front of the retina).
The receptors adapt to the presence of the pink dots within a few seconds, so that they appear a neutral grey. However, the rapidly moving grey dot remains visible because it is moving. However, because the eye has adapted to the pink, the grey looks green (it's the complement of pink).
Because the eyes always make very slight movememnts, the pink dots need to have blurred edges, so that slight movements on the retina don't cause them to reappear. A sharp edge which moved even very slighlty would be very obvious.
You don't even need a printed (or on-screen) illusion for this effect to be visible. Simply focus intently on one object spot, somewhere in your vision. For optimal effect, it's best to use one eye only, and hold it still (for best results, apply very gentle pressure through an eyelid to keep it absolutely still). Within a few seconds, everything in view will disappear, but as soon as you move your eye, it will reappear again.
Facebook
Twitter