Comparing models incorporating hypotheses about group differences in terms of reward sensitivity ρ or learning rate ϵ . Each bar of the large panel shows the Bayes factor comparing
. Green bars indicate very strong evidence for model
(Bayes factor ≥20), yellow bars weak evidence (Bayes factor 3−10) and cyan bars insufficient evidence (Bayes factor <3). MDD and high scores of anhedonic depression (AD) result in a reduction in ρ. Pramipexole instead reduces the learning rate. Stress has no differential effect on reward sensitivity compared with learning rate. Participants with a past history of depression, or euthymic individuals with bipolar disorder, showed weak evidence for a reduction in ρ. The insets at the top show the inferred priors over the relevant parameters of the winning model for each group.