1. Mehrabian, A. Communication without words. Psychol. Today 2, 53–56 (1968).
2. Ekman, P. & Friesen, W. V. Facial Action Coding System (Consulting Psychology Press, 1978).
3. Ekman, P. & Rosenberg, E. L. What the Face Reveals: Basic and Applied Studies of Spontaneous Expression Using the Facial Action Coding System (FACS) (Oxford University Press, 1997).
4. Harashima, H., Choi, C. S. & Takebe, T. 3-d model-based synthesis of facial expressions and shape deformation. Hum. Interface 4, 157–166 (1989).
5. Mase, K. An application of optical flow-extraction of facial expression. In IAPR Workshop on Machine Vision and Application 195–198 (1990).