Individual level effects of drug manipulations on choice behavior.
pain
Proportion of choices of the color associated with a higher chance of winning pain relief (placebo: n=28, levodopa: n=27, naltrexone: n=28) comparing the placebo condition to the levodopa condition (Lines connect individual proportions of choices of the advantageous option between placebo and the respective drug condition.In an additional exit interview at the end of each session, participants were asked whether they believed that one color of the wheel was associated with a higher chance of winning pain relief. The proportion of participants who reported this color correctly was not above chance (binomial test: p’s>0.5; placebo: 50%, levodopa: 37%, naltrexone: 39.3%). Nevertheless, participants’ belief whether one color of the wheel of fortune task was associated with a higher chance of winning or not significantly influenced their choices (p<0.001) and this influence on choices, and thus on learning, depended on the drug condition (interaction ‘drug × belief’: 