Three-Dimensional Dynamic Analysis of the Reproducibility of Verbal and Nonverbal Facial Expressions.

Objective: The aim of this study is to compare the short- and long-term reproducibility of verbal and nonverbal facial expressions of normal people using dynamic 3-dimensional (3-D) imaging.

Design: Prospective, cross-sectional, controlled study.

Setting: Peking University School and Hospital of Stomatology, Beijing, China.

Patients and participants: Twenty-seven participants, 12 males and 15 females, were recruited for this study.

Methods: A 3-D dynamic system was applied to capture the process of 4 nonverbal facial expressions (smile lips closed, smile lips open, lip purse, cheek puff) and 2 verbal facial expressions (/i:/, /u:/) at an initial time point, 15 minutes later, and 1 week later. Key frames were selected from each expression recording sequence.

Main outcome measures: The root mean square (RMS) between each key frame and its corresponding frame at rest was calculated. ΔRMS reflected the difference of the same key frames between the different sessions of the same expression of the same participant. The reproducibility of different facial expressions at different time intervals were analyzed.

Results: There was no significant difference in verbal and nonverbal expression repeatability during a 15-minute interval, except for cheek puff motion. Following a 1-week interval, verbal expression repeatability was superior to that of nonverbal expressions (P < .01). Compared with nonverbal expressions, the repeatability of verbal expressions did not obviously decrease with the increase in recording interval.

Conclusions: Dynamic 3-D imaging is a useful technique for facial expression analysis. Verbal expressions showed greater reproducibility than nonverbal expressions.