I would also say that the effect is in your head.
Many years ago, at a place where I used to work, we had a long narrow computer room.
At the end of the computer room was a colour monitor facing along the length of the room.
One day as a was walking towards the monitor, I noticed that the picture was jumping up and down.
Damn! I thought, another problem to fix.
When I got to the monitor and looked at it, the picture was completely steady.
Wow! Strange optical effect I thought.
After that, everytime I walked along that room, I noticed the same effect.
I cannot remember if I have noticed the same effect elsewhere.
JimB