Development of EMG-based criteria to evaluate the difficulty of realization of sign language: A potential contribution for understanding the negative hand paintings

The sign language uses a combination of complex finger and wrist configurations. The frequency of use of a particular sign is highly dependent on its physiological difficulty. However, no method allows to quantify accurately this difficulty. In the context of paleolithic negative hand paintings this absence of methods is problematic since the hand signs which are painted may be related to a primitive hand sign language. The objective of this study was to develop and validate a method based on electromyography recordings for quantifying sign language difficulty. Electromyography of the six main hand muscles were recorded and analyzed to determine individual muscle activity, summed muscle activity and muscle coactivation. Those results were correlated to subjective scales of difficulties to determine the electromyographic variables and/or the combinations of them which are good candidates for determining hand sign difficulties. Among all variables the summed muscle activities and the thumb muscle coactivation presented the most promising criterion. On the top of that, those criterions presented encouraging correlation with the frequence of occurrence of ten hand paintings of the Gargas Cave which open further studies for analyzing the origin of negative hand paintings.