What four items are you thinking of?

Cognitive researchers find that the average person is only aware of about four items at a time. People of higher mental ability can think of more, but lets stick with the four. When playing a game, how many of those four are dedicated to your game, and how many to other stimuli outside of games? Does each separate HUD element take up a channel, or does the entirety of the interface just take up one? Gets you thinking about exactly how much of the game the player is actually paying attention to...

I'll bet you that the story is the first thing to fall out of the player's attention rack when he has to worry about all the game mechanics that are requiring his attention in order to live.