Now you see it, now you don't.

The X effect or X’s fading, is a phenomenon where the subject fixates on a particular point, and a stimulus away from the fixation point, in peripheral vision, fades away and disappears. 

X's fading is attributed to the adaptation of the visual system vital for perceiving a stimulus. It is part of the general principle in sensory systems that an unvarying stimulus soon disappears from our awareness. X?



ANSWER : Troxler's Effect or Troxler's Fading