EKMAN, P. Three Classes of nonverbal behavior. Aspects of Nonverbal Communication. 1989
黒川隆夫. ノンバーバルインタフェース. 1994
WATANABE, T. A Voice Reaction System with a Visualized Response Equivalent to Nodding. Advances in Human Factors/Ergonomics, A. 1989, 12A, 396-403
WATANABE, T. Facial Expression Graphics Feedback for Improving the Smoothness of Human Speech Input to Computers. Advances in Human Factors/Ergonomics, A. 1991, 18A, 491-497