Early in his career, Dr. Ashby’s research focused on mathematical models of response times (RTs) and on the use of RTs to make inferences about underlying mental processes. In a typical behavioral experiment, the only dependent measures available on each trial are the accuracy of the response and the RT. Psychology has a 150-year-old history of research into the use of RTs to learn about the mental processes that mediated the behavioral response. Dr. Ashby’s many publications on this topic include an influential book (Townsend & Ashby, 1983) and many highly cited articles that make both empirical and theoretical contributions.