Fig. 4
A graphical illustration of the DDM. 0 and a are the two preset thresholds for the pro-social option and the selfish option, and a is a free parameter. Non-decision time, t0, denotes the time required for encoding the stimulus and decision execution. The three paths indicate the evolution of the relative evidence (R) over time. The red path which starts near the threshold of the selfish option represents the DDM process for a subject with a response bias towards the selfish option; the blue path which starts near the threshold of the pro-social option represents the DDM process for a subject with a response bias towards the pro-social option; and the black path represents a DDM process without starting point bias (unbiased DDM)
