Targets were followed by a feedback presentation, for which we had to limit our analysis to correct feedback due to trial-number limitations. The feedback elicited a broad centro-parietal component, which probably reflects a feedback-related P3 component. The response to the different kinds of positive feedback in the present experiment displayed sensitivities to reward in general, as well as to the difficulty of the task. The P3 component is generally known to be sensitive to expectancy (Courchesne et al., 1977; Johnson and Donchin, 1980; Núñez Castellar et al., 2010) and more specifically with regard to feedback, the P3 amplitude has been observed to be larger for unpredicted outcomes compared to predicted outcomes (Hajcak et al., 2005, 2007). Since in the current experiment correct feedback is more unexpected in high-difficulty trials than in low-difficulty trials, the main effect of task-difficulty might reflect this subjective expectation. The current findings related to reward are also consistent with previous reports showing larger P3 amplitude following reward feedback than no-reward feedback (Hajcak et al., 2007), which might indicate higher motivational significance of reward feedback (see Sato
