Appendix 1—figure 4. Test for an inverted-U relationship between choice behavior and DA baseline.

Choice behavior was assessed by four model-free choice variables (payout, %bestbandit, meanrank, %switches). DA baseline function was assessed by the two DA proxies spontaneous eyeblink rate (sEBR) and working memory capacity (WMC). For the latter, the first principal component across three different WMC tasks was used, denoted by WMC_PCA. Each plot shows two regression lines that were fitted to the data, one for the “linear model” (red line) and one for the “quadratic model” (blue line). Note that data from a pilot study and the placebo condition of the main study were combined for this analysis to increase the sample size to n=47. $\beta$: softmax parameter; $\phi$: exploration bonus parameter; $\rho$: perseveration bonus parameter.