None of the early sensory components elicited by the cues (P1 and N1) were modulated by our task manipulation (all p>0.1). The cue-related P2 component had a larger amplitude for reward cues than for no-reward cues, as indicated by a main effect of reward (F(1,21)=13.09, p=0.002; see figure 2A). Task difficulty did not influence the amplitude of this component (F(1,21)=1.65, p=0.21), and there was no significant interaction between the two factors (F(1,21)=0.14, p=0.71). The mean amplitude of the N2 component showed a trend-level main effect of reward (F(1,21)=3.63, p=0.07), with a larger amplitude for no-reward cues. No main effect of reward nor an interaction between reward and task difficulty was observed on this component (F(1,21)<1). Since the N2 follows the P2 very quickly, modulations of those components are not easily distinguishable. However, the most important finding here is that the reward availability is detected as early as 200 ms post-cue (P2 effect). The subsequent P3 amplitude was larger for reward cues compared to no-reward cues (F(1,21)=22.07, p<0.001; see figure 2B). No significant main effect of task difficulty (F(1,21)=2.86, p=0.11) or interaction (F(1,21)<1) was found for the P3 response.
