Investigating anticipatory processes during sequentially changing reward prospect: An ERP study

Performance-contingent reward prospect modulates the stability-flexibility balance in voluntary task switching. High reward prospect typically increases stability, indicated by a low voluntary switch rate (VSR). But this effect depends on the immediate reward history: Only when a high reward repeats (reward remains high), stability is increased. In contrast, when reward increases (high reward following low reward) cognitive flexibility is promoted, indicated by a relatively high VSR. To investigate the underlying mechanisms of changing reward expectations during voluntary task choice, we conducted two experiments and measured reward cue-locked event-related potentials (P2, P3b, CNV). The experiments yielded consistent findings: The P2 was stronger in response to high vs. low reward reflecting an early attentional boost by high reward anticipation. The P3b was highest in increase, intermediate in remain-high, and lowest in low reward trials suggesting responsiveness to working memory updating and motivational arousal. Finally, the CNV increased over time and was sensitive to both reward magnitude and sequence with the lowest amplitude in reward remain-low trials suggesting that preparatory control only increases when worth the effort. Taken together, early attentional processes (P2) were boosted by mere reward magnitude, while later processes (P3b, CNV) were sensitive to both reward magnitude and its sequence.