For the early part of the CNV an enhanced amplitude was found for reward-predicting cues (F(1,21)=19.41, p<0.001), while no main effect of task difficulty nor interaction between reward and task difficulty was observed (both F(1,21)<1; see figure 3B). Reward also modulated the late part of the CNV (F(1,21)=22.88, p<0.001), again with larger amplitudes for reward trials. Yet, this later main effect was modulated by an interaction between reward and task difficulty (F(1,21)=4.32, p=0.05; see figure 3C). This interaction resulted from the difference between high-difficulty and low-difficulty cues being larger for reward trials than for no-reward trials, with the largest late CNV deflection for high-difficulty reward trials.
