Vision is the last sensory system to be developed and the first to break down in performance. In fact, most people never fully develop their visual system. Vision is the first to be forgotten and is typically ignored. Yet, most of the consistent top performing baseball players took steps to better develop their vision--Tony Gwynn, George Brett, Rod Carew, Joe Morgan, Carlos Beltran, Mike Sweeney and many others.
The intricacies of the visual system take more time to develop and therefore develop later in life (perhaps not until the late twenties). Under stress (which occurs commonly in baseball), fine muscles tend to lose control, evidenced by voice breakdowns, loss of finger control evidenced by dropping things, and eyes start moving in random directions. Likewise, under stress people tend to become less visual and start paying attention to distractions.
- Dr. Bill Harrison