Figure 1.

Illustration of the diffusion model. The horizontal lines at 0 and a are the response boundaries. In this example, the boundaries are for “new” versus “old” responses in a recognition task. The line at z is the starting point, which varies from trial to trial across the range s_Z. The straight arrows show average drift rates, and the wavy lines represent the actual accumulation paths that are subject to moment-to-moment noise (s). Three average drift rates are shown to illustrate the across-trial variability in drift, which is normally distributed with a standard deviation of η. Predicted response time distributions are shown at each boundary.