Using Dynamical Simulations to Quantify Affordances in the Task Space for Throwing to Hit Distant Targets
36.544, Sunday, May 12, 2:45 - 6:45 pm, Vista Ballroom
Andrew Wilson1, Andrew Weightman2, Qin Zhu3, Geoffrey Bingham4; 1Leeds Metropolitan University, 2Manchester Metropolitan University, 3University of Wyoming, 4Indiana University, Bloomington
Introduction Throwing to hit distant targets requires perception of target distance and height. This information must then be used to control both release angle and speed of the projectile. These two action parameters trade off to allow target hits. Some regions of the parameter space yield greater latitude in parameters that yield a hit, affording the most reliable performance. Do expert performers perceive this affordance to operate in these more stable regions? Methods We tested expert throwers in two studies. Participants threw balls to hit a 4ft x 4ft vertical target. In Experiment 1, we manipulated target distance (5m, 10m, 15m) and height (1m, 1.5m, 2m). In Experiment 2, we manipulated target distance (5m, 10m, 15m), orientation (vertical, horizontal), and vision (monocular, binocular). We performed dynamical simulations of hit/miss across a wide range of release parameters to map stability in the task space. We then mapped the experts performance within this space. Results For vertical targets, release speeds were high and scaled with distance. Release angles were low and scaled with both distance and height. The horizontal target then forced experts to throw high and slow, which they readily did. Monocular vision only affected throws to vertical targets; poorer resolution of distance yielded slower throws compensated for by increased angles. Dense simulation of the parameter space allowed us to quantify the affordances. Experts do operate in regions of the space with optimal stability (i.e. hits over wide variation in release angle). Conclusion The dynamics of throwing to distant targets yield a task space specified in terms of two action parameters, release angle and speed, that determine successful action. Mapping the structure of this space reveals regions affording reliably successful performance. Expert throwers exhibited sensitivity to this affordance, performing within these more stable regions.