A prominent feedback-related component that was visible over posterior central electrode sites showed a significant main effect of reward (F(1,21)=105.33, p<0.001), with larger positive amplitudes for the reward condition compared to the no-reward condition. The main effect of task difficulty was also highly significant (F(1,21)=127.99, p<0.001) due to more positive amplitudes for high-difficulty than low-difficulty trials. Moreover, a highly significant interaction was observed (F(1,21)=29.82, p<0.001), explained by a larger amplitude difference in high-difficulty versus low-difficulty trials in the reward condition compared to the no-reward condition (see figure 4B).
