A Gibsonian Motor Analysis of the Nut-Cracking Technique

Abstract

Nut-cracking may be described as the action of choosing a stone with one hand, positioning the nut on an anvil with the other hand, and hitting the nut with a ballistic movement. A functional description of the nut-cracking action will consider the mechanical properties that must be satisfied to succeed in the task at hand, that is, the mechanical energy produced through the movement. In the wild, chimpanzees have been observed to select the appropriate tools, that is, size, shape, and material of hammer and anvil, suggesting that chimpanzees do control the functional properties of the nut-cracking task. However, these studies do not analyze how the action is processed. In this chapter, we propose to focus on the chimpanzees’ capacity to perceive the functionality of the tools and on how the functional characteristics of the task are generated. Taking a Gibsonian perspective, we discuss some dimensions of the functional coupling between the animal and its environment as can be seen in a controlled nut-cracking experiment. The behavior of the animal is analyzed at two levels of action: the choice of the best tool that fit the goal, and the capacity of the chimpanzee to adapt his or her behavior to the properties of the tool and of the nut.