In addition to Mike's suggestionanswer, see the Ratcliff diffusion model and variants thereof. E.g.:
Ratcliff, R., & Rouder, J. N. (1998). Modeling response times for two–choice decisions. Psychological Science, 9, 347–356.
Ratcliff, R., & Tuerlinckx, F. (2002). Estimating parameters of the diffusion model: Approaches to dealing with contaminant reaction times and parameter variability. Psychonomic Bulletin & Review, 9, 438–481.