Quantitative anatomical analysis of facial expression using a 3D motion capture system

Abstract

Facial muscles are attached to the facial skeleton or membranous fascia beneath skin or subcutaneous tissue. The topography of the facial muscle varies between males and females, as well as between individuals of the same gender. It is important to define muscle shapes, their associations with the skin, and their relative functionality in order to explain the unique expressions that people can make. Three-dimensional motion-capture analysis is often used to study facial expression, and this study used such a system to identify characteristic movements of the skin of both males and females when they were making six representative basic expressions (fear, pleasure, surprise, anger, sadness, and disgust) based on the movements of 44 reflective markers (RMs) positioned on anatomical landmarks. The mean displacement of the RMs was large in males [ranging from 14.31 mm (fear) to 41.15 mm (anger)], and 3.35-4.76 mm smaller in females [ranging from 9.55 mm (fear) to 37.80 mm (anger) mm]. In males and females the percentages of RMs involved in the ten highest values of the mean maximum displacement when making at least one expression were 47.6% and 61.9%, respectively. In males, the movements of the RMs were larger but tended to be more limited in area compared to those in females. Expanding our understanding of facial expression requires morphological studies of facial muscles and studies of related complex functionality. Conducting these studies together with quantitative analyses such as that performed the present study will yield vital data for use in the fields of medicine, dentistry, and engineering, such as for surgical operations of facial regions, software for predicting changes in facial features and expressions after corrective surgery, and the development of face-mimicking robots.