Former MLB pitcher Dave Baldwin (Sox, 1973) explains the brain's functioning during the 4/10 of a second between release and contact.
Snip:
The batter needs to begin collecting pitch information as soon as possible. To prepare for this "quick read," the batter’s conscious mind concentrates on an imaginary "box" where he expects the pitcher’s release point to be. Thus, his cerebral cortex is thoroughly occupied and doesn’t hinder the unconscious mind. If he has guessed correctly and the ball is released from that box, he can begin to evaluate the pitch as it leaves the pitcher’s hand. Otherwise, the batter must spend precious milliseconds searching for the ball.