Fig. 1.

Reinforcement learning task involving right hand and right foot responses. (a) Task design. On half the trials (‘abort’ trials) the slot machine disappeared before the Go signal and the next trial started; on the other half (‘response’ trials) lights on the slot machine would turn green, serving as a Go signal; participants responded by pressing force-sensitive buttons with either their right hand or foot. Feedback was then presented consisting of either “+ £2.00” in green, or “+ £0.00” in red. (b) The probability of obtaining the reward varied over time per response, and per slot machine. This meant participants were required to track 4 random walks that varied between p (reward) of 0.15 and 0.85.