Baseball outfielders maintain a linear optical trajectory longer than optical acceleration cancellation when pursuing uncatchable fly balls

Purpose. We previously reported that baseball outfielders initially maintain both a linear optical trajectory (LOT) and optical acceleration cancellation (OAC) for baseballs that they catch (Science 268, 569-573). Fielders appear to preferentially utilize the more sensitive spatial LOT cue when balls are hit to the side. The present work further tests cue preference by comparing how well fielders maintain a LOT versus OAC when pursuing uncatchable balls. Methods. We used shoulder and head mounted video cameras on experienced outfielders and recorded the optical ball trajectory for 30 cases in which they were unable to get to and catch the ball. We compared the lengths of time that fielders maintained a LOT versus OAC as well as the variance accounted for by OAC during the period that a LOT is maintained. Results. The results indicate that when balls are directed too far in front of fielders, they maintain LOT and OAC for about the same lengths of time. When balls are directed too far beyond or over the fielders heads, they maintain a LOT significantly longer than OAC. Fielders apparently adjust their lateral running speed to produce lateral optical ball movement that accelerates at the same rate as vertical optical ball movement. Conclusions. Our findings further empirically support the idea that baseball outfielders preferentially attend to spatial over temporal cues when trying to catch fly balls. The results relate human tracking behavior to vehicular, nautical and ballistic tracking algorithms that produce collisions by utilizing the perceptually invariant property of constancy of relative angle of motion.