I view it as a function of smooth pursuit eye movement. While watching the ball move you are also unknowingly watching other stimuli around the ball in the background. The combination allows your eyes to track the path the ball is traveling. This is why pitchers focus so much on making pitches look alike. The further the ball travels before the hitter sees a recognizable difference, the harder it is to adjust.Seeing spin and adjusting is certainly something I did (or tried to at least) but the adjustment is a reactionary one based upon past experience of seeing curves..your brain extrapolates based upon previous experience to try and determine where the ball is going to end up and you (reactively) adjust your swing accordingly. I see that as being different than attempting to hit a certain part of the ball.