 In simplest terms I'm just going to tell you to not have any head movement while you hit. Yes, your eyes will move, but not your head. If your head starts moving up and down or side to side then it's going to throw off your perception of where the ball is and where the ball is heading (no pun intended). A hitter does not track the ball with his head. Period.
Take that picture to the right as an example, see what happens when you don't move your head? You go to the playoffs. Seriously though, if you could look at this swing frame by frame you would see very little, if any head movement.
It doesn't matter if you have an open stance, a closed stance or a regular stance....your head shouldn't move. Long time hitting guru Walk Hriniak is a big time believe in minimal head movement so if you are looking for good examples you should check out players like Frank Thomas, Wade Boggs and Robin Ventura. | 
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head movement = shanks......oh wait that's golf, but what is good for the goose is good for the gander....whichever sport. seriously.....you move your head you lose your point of reference from where you started. if you don't know where you started then how can you even guess at where you'll finish.
I should have just let you write the post. That's exactly the point I was trying to get across. In baseball, I believe, you have more moving parts in the bottom half of your body that can make your point of reference askew. Alfonso Soriano is a good example of this because when he's going poorly he'll start his stance crouched and as he moves to hit the ball he'll uncrouch and then recrouch which makes his line of vision completely screwed. Not sure if that can happen in golf?
not only that, but when you are hitting there is a pivot running vertically through your body. To put it bluntly it goes in through the top of your head and out through your ass. You may turn the pivot as you screw up to swing, and turn it agains as your hips pull your trunk into the cut, but the pivot should stay in the same alignment (if I am reading between the lines of The science of Hitting properly). If you move your head around in relation to your trunk you squirrel the pivot around and that will do all sorts of wonky things. I always know when I am leaning my head in because I end up pushing may hands out away from my body and contacting the ball off the neck of the bat. I did it in my first at bat Wednesday and was lucky it dropped in for a hit.