As with most things governed by the mind, visual perception does not conform to strict rules. A recent study by Jessica K. Witt and Dennis R. Proffitt at the University of Virginia in Charlottesville confirms that athletes perceive the ball to be larger or smaller, depending on how well they are playing.The researchers showed a chart with circles of various sizes to softball players who had just been in a game and asked them which circle best matched the size of the ball. They found that those who had had better batting averages that day chose the larger circles and that those who had played poorly picked the smaller ones. Perhaps batting helmets could incorporate visors with magnifying lenses to boost performance?The researchers’ report, published in Psychological Science in December, wasn’t clear about whether seeing the ball as bigger helped the hitter connect or whether hitting well affected the visual memory, making the ball loom larger in retrospect. In any event, poor Casey must have thought he had been swinging at a marble.