Consistency of Virtual Human Faces: Effect of Stylization and Expressiveness Intensity on Character Perception

Abstract

The perception of virtual human faces is impacted by several interrelated factors, such as shapes, materials, textures, shading or animation. Previous research demonstrated that animation flaws and inconsistencies tend to be less accepted on realistic characters compared to stylized ones. To further investigate the relationship between stylization and facial expressions, we designed an online investigation to assess participants' perception of virtual human faces with regards to perceived realism, attractiveness and eeriness. We modeled a female and a male character with three levels of stylization (stylized, semi-realistic, realistic) and four expressiveness intensities (idle, low, moderate and exaggerated). 135 participants took part in the experiment which consisted of watching a set of 24 videos lasting 30 seconds each. Interaction effects were observed between the independent variables. Overall, results indicated that perceived realism was mainly driven by the stylization level. Visually realistic characters were perceived as more realistic even with exaggerated facial expressions. In terms of attractiveness, scores tended to decrease as the intensity of facial expressions increased. At the highest expressiveness intensity, the semi-realistic female character was preferred over the stylized and the realistic ones, while the realistic male character scored higher than the others. In line with previous studies, results indicated that perceived eeriness rises with the intensities of facial expressions. Taken as a whole, this study provides valuable guidelines for 3D artists and developers to design avatars and autonomous agents.