The old saying that the ball looks bigger when you're in the zone? There's something to it.
When she was a grad student, Jessica Witt, now of Purdue University, sought to study
(pdf) whether players perceive the size of the ball differently based on their recent performance. Outside some softball fields, Witt gave away sports drinks in exchange for something more valuable: information. She wanted to know how the players hit during the game, and she asked them to look at a board with various circles close to the true size of a softball and pick out which circle was correct.
Players fresh off a great day at the plate, she found, pointed to the larger circles, while those who had struggled at bat tended to point at smaller circles.