Although a main effect of task-difficulty was found for RTs, there was no clear difference between CNV amplitudes in high-difficulty no-reward trails and low-difficulty no-reward trials. This might be explained by a motivational account, in which additional strategic attention is employed only when it is worth the effort. Therefore, no extra preparation processes will be triggered by high-difficulty cues in situations without the potential of being rewarded. The current finding is probably context-dependent, since participants usually also engage attentional resources in difficult tasks that lack (the prospect of) reward. In the current experiment, however, no-reward trials could be seen as disappointing leading to a lack of motivation to spend processing resources on these trials. Alternatively, control processes elicited by task difficulty might be qualitatively different in the reward condition and the no-reward condition along the lines of a pro-active vs. re-active distinction (e.g., Braver, 2012). Specifically, high task-difficulty in a reward context clearly engage pro-active control mechanisms, as indexed here be the CNV. In contrast, different levels of task difficulty in the no-reward condition of the current experiments might have
