1. J.J. Nilson, ``Shakey the Robot,'' tech. note 323, SRI AI Center, Menlo Park, Calif., 1984.

2. D. Beymer and K. Konolige, ``Real-Time Tracking of Multiple People Using Continuous Detection,'' IEEE Frame Rate Workshop, 1999; available at www.eecs.lehigh.edu/~tboult/ FRAME/Beymer (current 31 Aug. 2001).

3. N. Badler, M. Palmer, and R. Bindiganavale, ``Animation Control for Real-Time Virtual Humans,'' Comm. ACM, vol. 42, no. 8, Aug. 1999, pp. 64--73.

4. H.H. Clark and S.A. Brennan, ``Grounding in Communication,'' L.B. Resnick, J.M. Levine, and S.D. Teasley, eds., Perspectives on Socially Shared Cognition, APA Books, Washington D.C., 1991, pp. 127--149.

5. L. Steels, ``The Origins of Syntax in Visually Grounded Robotic Agents,'' Artificial Intelligence, vol. 103, nos. 1--2, 1998, pp. 133--156.

6. Y. Yokote, ``The Apertos Reflective Operating System: The Concept and Its Implementation,'' Sigplan Notices, vol. 33, no. 10, 1992, pp. 414--434.

7. M. Fujita and H. Kitano, ``Development of an Autonomous Quadruped Robot for Robot Entertainment,'' Autonomous Robotics, vol. 5, 1998, pp. 1--14.

8. L. Steels et al., ``Crucial Factors in the Origins of Word-Meaning,'' The Transition to Language, A. Wray et al., eds., Oxford Press, UK, to be published 2002.

9. L. Steels and R.A. Brooks, eds., The Artificial Life Route to Artificial Intelligence: Building Embodied Situated Agents, Lawrence Erlbaum Associates, Hillsdale, N.J., 1995.

10. C. Breazeal, ``A Motivational System for Regulating Human-Robot Interaction,'' Proc. AAAI98, AAAI Press, Menlo Park, Calif., 1998, pp. 31--36.