Visual judgements and misjudgements in cricket, and the art of flight.

To hit the ball with the centre of percussion of a bat so that the ball goes where he intends it to go, a batsman must estimate visually where the ball will be at a specific future time (when), and coordinate his swing accordingly. A number of visual cues are available to the batsman. Retinal image information provides an accurate indication of time to contact (ie when), even when the trajectory of the ball is inclined to the line of sight, and there is evidence that the human visual system is specifically sensitive to time-to-contact information. But only part of the necessary information about position (ie where) is available to the batsman. If the batsman's head is directly in the line of flight, the velocity ratio of the retinal images in the left and right eyes provides a precise cue to the trajectory of the ball in the horizontal plane. However, humans have only poor visual sensitivities to the absolute distance and to the line-of-sight velocity of a ball. Therefore, a batsman has inadequate retinal image information about the absolute vertical velocity of a ball. It is suggested in this paper that batsmen supplement inadequate retinal image information about where the ball will hit the ground with prior knowledge built up over the preceding few deliveries. Some slow bowlers can induce the batsman to misjudge where the ball will hit the ground. I suggest that these bowlers manipulate the flight of the ball so as to induce the batsman to supplement his inadequate retinal image information with inappropriate prior knowledge, and thus to misinterpret the vertical angular speed of the retinal image of the ball.