Visualization and analysis of skin strain distribution in various human facial actions

Human faces are mechanical systems that display emotional and linguistic information with motions of the deformable facial tissues. Since each facial action forms a different stress-strain field that characterizes the differentiated facial appearance, a detailed analysis of strain distributions for each facial action will contribute to analytical and synthetical studies on human faces. This study evaluated strain distributions of 44 facial actions of a Japanese adult male based on the three-dimensional displacements of 125 tracking markers attached to the facial surface. We investigated how much the facial skin surface is stretched and compressed in each facial region based on the evaluated area strains produced by each facial action. Then, we visualized the strain distributions and surface undulation to analyze the complexity of the deformations on a face. The results show that the positive and negative surface strains intermingled on a face even in simple facial actions, potentially reflecting the complex facial structure under the facial skin layers, where several tissues with different material properties, e.g., adipose tissues and retaining ligaments, are distributed heterogeneously. These results are beneficial for artificial face designers as a design target and evidence to consider the effective skin structure and locations of actuators for artificial faces.