How does your observation of another objects motion depend on your motion?
Your observation of motion depends on your own motion in that depending on your speed and course. Objects closer to you will seem to move while those at a far distance will seem constant.
Look out the window when you're in a car, the closer objects, houses for example, seem to zip by, but the trees in the distance are barely moving. it's an optical illusion.
Or a car next to you. If you're going 60 and the other car is going 55 then in your mind it looks like its going 5mph.