Hefting for throwing is not a smart mechanism

Bingham, Schmidt and Rosenblum (1989) found that people could, by hefting objects of different sizes, choose that of optimal weight in each size for throwing to a maximum distance. Larger weights were chosen in larger sizes as required for equivalent perceived heaviness according to the size-weight illusion. In Experiment 1, we replicated that result testing a larger range of objects and more participants. Bingham, et al. (1989) had hypothesized that hefting acts as a smart mechanism to allow objects to be perceived in the context of the dynamics of throwing. This hypothesis entails two assumptions. The first is that hefting by hand would be required to provide information about throwing by hand. We tested and confirmed this in Experiments 2 and 3. We also tested the possibility that hefting using the foot yields information about throwing using the foot. It did not. The second assumption is that optimal objects are determined solely by the dynamics of throwing. We used the mean distance of throws found in Experiment 1 together with object sizes and weights to perform simulations of projectile motion and recover release velocities. The results showed that only object weight, not size, affected throwing. This result disconfirmed the smart mechanism hypothesis. Because the affordance relation is determined in part by the dynamics of projectile motion, the conclusion is that the affordance must be learned from knowledge of results of throwing.