Effects of time function and expression speed on the intensity and realism of facial expressions

In this paper, the effects of dynamic facial expression properties on the recognition of emotions were investigated. Although many studies of facial expression recognition and analysis have been conducted, the stimuli used in these experiments were typically static. Even when dynamic facial expressions were used, the experimental task was restricted to the basic expressions. In natural communication environments, facial expressions are often subtle or ambiguous. Studies of the analysis and synthesis of subtle and dynamic facial expressions are therefore required. As a quick going up expression could be recognized as a different emotion from a slow rising one, we represented facial expressions as the combination of time function of intensity and presentation speed. Experiments using stimuli that were combinations of four intensity time functions and three presentation speeds were conducted. Participants rated the perceived intensity of the emotions depicted, as well as how realistic they appeared to be. Time function and speed had different effects on different emotions, i.e. perceptions of anger were affected by set up speed, and the perceived intensity and realism of smiling expressions were also affected by speed.