[shrinks99]

You can see everything in your field of vision, but the area DIRECTLY in the centre has the highest level of detail. This image has high frequency animated details that are not cognisized equally by your entire FOV. The animated bit right in the middle at any given time is where your brain processes the most detail and also where you are looking.

[Peteragain]

I had to think about it, but are you saying all the stars are animated to rotate, but the amount they move between frames is too small for you to see unless it's in your fovea?

[Sharlin]

They're just so small that you only see shapeless blur outside your fovea. If you applied an artificial blur filter to the whole screen, you'd also not see any movement anymore because all high-resolution detail is removed. A 3x3 box blur will erase differences between

  X X        X
   X   and  X X
  X X        X

[pxndxx]

They are tiny and the ones not on your fovea don't register enough "pixels" for your brain to recognise the rotation.

[BriggyDwiggs42]

Oh cool so it’s about the frequency?

[robotresearcher]

Spatial frequency, ie. small detailed things, not temporal frequency (in this example).