Figure 1.

Graphical illustration of the experimental paradigm. (A) Participants were presented with the potential outcomes, for example a certain amount of money (upper row) or food (lower row). Participants then bid how many seconds (0–10 s) they would be willing to apply 50% of their maximal grip force in order to receive the displayed reward. If their bid was greater or equal to the random number (upper trial), they had to perform the action which was visualized as the small white filled square going inside the white unfilled rectangle. Otherwise (lower trial) they did not have to do anything but did not win the reward. Lastly, these bids were used to match the monetary and food reward to the subjective value of the social reward. (B) During the instrumental conditioning, participants either used their dominant (upper trial) or non-dominant hand (lower trial) to reach the target, which was set on 15% of their maximal grip force. If the cursor was held between 2 s and 4 s within the target they received a reward. Each hand was paired with one randomly assigned reward type (i.e., money for squeezing with the dominant hand, food for squeezing with the non-dominant hand). (C) During the Pavlovian conditioning, participants learned four associations between fractals and outcomes. Three outcomes were rewarding, whereas two of them were the same as during instrumental conditioning (upper two trials) and one was neutral (last trial). (D) During the Pavlovian-to-instrumental transfer, participants performed the same task as during instrumental conditioning but bimanually and under extinction. The same stimuli as in Pavlovian conditioning were shown in the background.