Dirkin, H. K., Mishra, P., & Altermatt, E. (2005). All or nothing: Levels of sociability of a pedagogical software agent and its impact on student perceptions and learning. Journal Educational Multimedia and Hypermedia. 14(2), 113-127.

Abstract:
This article reports the results of an experimental study on multimedia learning environments, which investigated the impact of increasing the social behaviors of a pedagogical agent on students’ learning experience, and learning. Paradoxically, in this experiment students detected higher degrees of social presence in both the text only and the fully animated social agent conditions than students in the voice only and static image of the agent with voice conditions. Furthermore, students had more positive perceptions of the learning experience in the text only condition. The results support the careful design of social behaviors for animated pedagogical agents if they are to be of educational value, otherwise, the use of agent technology can actually detract from the learning experience.