Not a matter of shape: The influence of tool characteristics on electrodermal activity in response to haptic exploration of Lower Palaeolithic tools

Abstract

Objectives Haptics involves somatosensory perception through the skin surface and dynamic touch based on the proprioceptive response of the whole body. Handling Palaeolithic stone tools influences the arousal and attentional engagement, which can be detected and measured through electrodermal activity. Although tool shape has generally been studied to consider tool functions or tool making, it is also a major factor in tool sensing and haptic perception. The purpose of this survey is to analyze whether the electrodermal reactions are influenced by stone tool morphology. Methods We first quantify the morphological variability of 72 stone tools through geometric morphometrics. Then, 12 stone tools from the previous sample were randomly selected to perform the electrodermal analysis in a sample of 46 right‐handed adults. Results Elongation is the main factor involved in Lower Palaeolithic shape variation, followed by the position of the maximum thickness. Attention and manipulation time are mainly influenced by tool size, while arousal mostly correlates with tool weight. Electrodermal activity is apparently not influenced by the overall tool shape. Tool size, weight, and base morphology are the variables that mainly trigger an electrodermal reaction. Conclusions Electrophysiological reaction is more sensitive to specific physical features of the tool than to its general outline. These features are not particularly different in worked pebbles and handaxes in terms of grasping, but underwent remarkable changes in other technological traditions. That changes associated with behavioral performances can be employed in cognitive archaeology to investigate the relationships between tool sensing and tool use.

Lower Paleolithic Shaped Stone Balls—What Is Next? Some Cultural–Cognitive Questions

“…When comparing choppers with handaxes in terms of shape, we can see that the main pattern polarising their morphological variability is the degree of elongation, while the second factor involved is the longitudinal position of the maximum thickness [53] (. The first factor (elongation) separated the two tool typologies (although with a certain degree of overlap), while the second source of variation (the longitudinal position of the maximum thickness) is shared by both types of tools [55]. If we plot a perfect sphere into Hand palm (black dots) and stone ball (red dots) length and width.…”

“…A perfect sphere (black dot), in this case, lies in the centre of the choppers' range. Data from [55].…”