Abstract
Autonomous synthetic characters have the potential to promote the social engagement of users in virtual environments, thus enhancing their interaction experience. This effect is supported by the interactions between users and synthetic characters perform together, which are often in group scenarios. However, for these group interactions to be successful, it is not enough to assure that the characters behave in a coherent manner from an individual perspective, but it is also necessary that they exhibit behaviours that are coherent with the group's composition, context and structure. Therefore, we have developed a model to support group dynamics of autonomous synthetic characters (SGD Model), inspired in theories developed in human social psychological sciences, that define the knowledge that each individual should build about the others and the group, and how this knowledge drives their interactions. This model was used to drive the behaviour of characters in a collaborative computer game that was used in an experiment that showed that the SGD Model had a positive effect on the users' social engagement, namely on their trust and identification with the group.