Not at all a silly question.
The receptors in the eye send signals to the brain instantaneously when light hits them, triggering chemical changes which the brain recognizes. It assembles all the random "pixels" into objects.
When you play a game, the "objects" are animated by the brain by interpolating between the objects' positions between frames. The more frames the game generates, the smoother the animations.
With time the brain can become more adept at this. i.e. if you're just starting to play graphic-intensive games then it may take thirty or forty FPS to satisfy the brain. I've been playing these types of games for about three years, and it has to get down to about fifteen before it interferes with my playing. Some veteran gamers can put up with ten (not that they won't get annoyed by how stupid it looks).
So basically, 24-30 FPS (the standard in both TV and computers) should be plenty for most games, and beyond 40 you can't really see any difference.
I hope this helped.
Oh, just another observation of my own:
If you start playing video games at a young age (first-person shooters and racing games in particular), you will be impervious to motion sickness for life!