The role of expertise in tool use: Skill differences in functional action adaptations to task constraints.

Abstract

Tool use can be considered a particularly useful model to understand the nature of functional actions. In 3 experiments, tool-use actions typified by stone knapping were investigated. Participants had to detach stone flakes from a flint core through a conchoidal fracture. Successful flake detachment requires controlling various functional parameters simultaneously. Accordingly, our goals were twofold: (a) to examine the regulation of kinetic energy by varying the properties of the hammers and the goal, and (b) to characterize the difference in action regulation across skill levels. All groups were able to modify their actions according to changes in task goals, but only experts displayed fine-tuning to functional parameters (i.e., regulate actions according to changes in hammer weight in a manner that left kinetic energy unchanged). Expertise is considered to depend on the identification of the interactions between functional parameters.

Functional mastery of percussive technology in nut-cracking and stone-flaking actions: experimental comparison and implications for the evolution of the human brain

“…While all knappers showed greater velocity when using a lighter hammer, these variations do not end up in the production of the same kinetic energy when using a light or a heavy hammer. The adaptation to the hammer weight that was observed for velocity does not transfer to kinetic energy, except for experts (figure 6; [29,56]). …”

“…A peculiarity of the kinetic energy necessary to produce a conchoidal fracture is the existence of a threshold value. Once a minimum effective quantity of kinetic energy is produced, an increase in this value has no impact on the flake produced, except that a value far too large may cause the flake to fragment into many pieces (reference in [29]). As such, the characteristics of the flake (its dimensions and form) depend on the convergence of multiple interrelated variables [56,57,59].…”

“…To what degree are chimpanzees and humans able to adapt to the hammer properties to crack nuts or to knap stone? We conducted experiments to evaluate the capacity of the actor to cope with the constraints of the task by comparing the values of kinetic energy produced when the actor had to use hammers of different weights [29,32,64]. All actors (humans and chimpanzees) were able to modify the velocity they produce to the changing constraints of the task; in all cases-i.e.…”

“…(a) Material and methods We briefly present our methods and subject populations here; more details can be found in our papers reporting the primary results [29,32,33,56,[61][62][63][64][65][66]. We designed experiments to investigate how actors of various levels of expertise develop specific behavioural traits concerning movement precision, flexibility, smoothness, regularity and optimization [67,68] (cf.…”

“…To characterize the skills needed for percussive techniques of nut cracking and stone flaking, we differentiate four layers of parameters [29] defining (respectively) the functional and deterministic task constraints, the parameters under the control of the actor performing the task and the parameters that determine effective regulation of these control parameters and movement parameters (figure 1). The functional parameters specify the topology of the task through relevant geometric and dynamical parameters, including kinetic energy, point of percussion, angle of blow and (for stone knapping) exterior platform angle.…”