Fig. 1.

The diffusion model and its parameters. Evidence accumulation begins at z, proceeds over time guided by drift rate v, and halts when either the upper or the lower boundary is reached, the distance between which is boundary separation a. Observed RT is an additive combination of the time during which evidence is accumulated and the non-decision time T _er. Note that non-decision time consists of stimulus encoding (prior to the decision process) and response execution (after the decision process)