Subtle emotional expressions of synthetic characters

This study examines the influence of the geometrical intensity of an emotional facial expression on the perceived intensity and the recognition accuracy. The stimuli consisted of synthetic faces at ten geometrical intensity levels in each of the five emotional categories. A curve-linear relationship was found between geometrical and perceived intensity. Steps of 20% geometrical intensity appear to be appropriate to enable the participants to distinguish the intensity levels. At about 30% geometrical intensity the recognition accuracy reached a level that was not significantly different from each emotions maximum recognition accuracy. This point indicates a categorical perception of the facial expressions. The results of this study are of particular importance for the developers of synthetic characters and might help them to create more subtle characters.