The green dot is not real -- it is an afterimage.
The dots are not actually disappearing -- that is Troxler's fading.
The apparent motion is the phi phenomenon.
Lilac Chaser (Pac-Man Illusion)
Stare at the fixation cross. You will see:
1. A green dot chasing the gap (afterimage)
2. Lilac dots fading away (Troxler's effect)
3. Apparent motion of the green phantom (phi phenomenon)
Three separate visual phenomena combine into one beautiful display: chromatic adaptation, neural adaptation, and apparent motion.