Sequence Analysis of Grip and Manipulation During Tool Using Tasks: a New Method to Analyze Hand Use Strategies and Examine Human Specificities

Different factors may have coevolved with hand dexterity such as bipedalism, brain enlargement, language, and the production and use of stone technology. Prehistoric stone tools are thus probably one of the key elements to examine the origin and evolution of these essential functions during human evolution. To gain a better understanding of the variability of traces resulting from use found on stone tools or on the body of the user, to better infer past archaeological tools, and to assess what the tool-using human hand specificities are, it is essential to investigate and describe tool manipulation itself. Studies investigated this question but either focused on static finger postures during grasping, or involved complex kinematic model of the coordination of the fingers necessitating the pose of many markers on the hand excluding the application of the method on non-human species. Here, we propose a new method to describe and quantify the dynamic strategies of tool grip and manipulation without the need of markers. We tested this method on five human subjects who had to make bamboo points using flint flakes. Time-based sequence analysis allowed identifying and describing both consistency and variation among users and types of use depending on the observed variable (e.g., hand contact areas, repositioning). The method proved to be efficient and, to our knowledge, is the only available method to describe and quantify with such detailed level grip and manipulation as dynamic process in both human and non-human primates without high technical constraint.