1. Yahoo Labs, 701 1st Ave., Sunnyvale, CA 94098, U.S.A.
2. University College London, Alexandra House, 17 Queen Square, London, WC1N 3AR, U.K.
3. Disney Research Pittsburgh, Pittsburgh, PA 15213, U.S.A.
4. Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
5. Tokyo Institute of Technology O-okayama, Meguro-ku, Tokyo, 152-8552, Japan