At Carnegie Mellon, Lee worked on topics in machine learning and pattern recognition. In 1986, he and Sanjoy Mahajan developed Bill,[14] a Bayesian learning-based system for playing the board game Othello that won the US national tournament of computer players in 1989.[15] In 1988, he completed his doctoral dissertation on Sphinx, which he claims is the first large-vocabulary, speaker-independent, continuous speech recognition system.[16]