LEARNING AFFRODANCES FOR MAXIMUM DISTANCE THROWS IN THE CONTEXT OF LEARNING TO THROW

Abstract

By hefting objects in the hand, people are able to judge the object affordance (the optimally weighted object at a given graspable size) for maximum distance throws (Bingham at al., 1989; Zhu & Bingham, in press). This affordance corresponds to a relation between object size and weight and distances of throws, that is, a single valued function (disance) in two variables (size and weight). The present study first explored whether this affordance could be learned with the acquisition of throwing skill, and second attempted to identify whether the acquisition of this affordance is a type of function learning (Busemeyer & McDaniel, 1997) or the acquisition of a smart perceptual mechanism (Bingham, et al., 1989). 24 unskilled adult throwers were asked to heft 48 objects of different sizes and weights, and to judge their affordances for the maximum distance throws. A month long intensive practice of throwing was then administered, for which participants were divided into 4 groups so that 3 groups practiced throwing with vision using 3 prescribed sets of 6 objects each (constant size, constant weight or constant density) but the 4th group without vision using the set in constant density. After practice, hefting judgments, throwing and then hefting judgments again were tested with the full set of 48 objects. The results showed that participants, were unable to perceive the affordance before practice, however, as throwing skill was acquired through practice and the visual perception of throwing distance was provided, their sensitivity to the affordance improved independently of the prescribed set of objects, and finally, accurate perception of the affordance was acquired. Study also confirmed that only object weight affected the dynamics of throwing to determine the release velocity although the throwing distance was determined jointly by object size and weight. The results indicated that the affordance was perceived using a smart perceptual mechanism that was also acquired as participants learned to throw.