Action or Stimulus: Individual Beliefs About Learned Associations Influence the Processing of Immediate and Delayed Feedback.

Feedback learning seems to involve two systems, the striatal reward system and the medial temporal lobe (MTL), which have both been linked to event-related potential (ERP) components such as the feedback-related negativity (FRN)/N2, overlapped by a reward positivity (RewP), and the N170, respectively. In this study, we tested the hypothesis that the former system is more involved in associating the feedback with previous actions and the latter in associating the feedback with previous stimuli. More specifically, we hypothesized that the engagement of these systems depends on individual beliefs in credit assignment, that is, whether participants linked the feedback they received to actions or stimuli, possibly modulated by feedback timing. Electroencephalography (EEG) data were recorded from 43 participants performing an ambiguous feedback-learning task, in which feedback could be attributed to either a performed action or a selected stimulus, according to the instruction. As revealed by an Action Index derived from behavioral data, the focus on stimulus-feedback associations was generally stronger than that on action-feedback associations. We found that both FRN/N2 and N170 were influenced by individual beliefs about learned associations, with the FRN/N2 showing stronger feedback valence coding across feedback delays when participants took action-feedback associations into account. Also prediction error coding in the N170 was more pronounced for stronger action-feedback association learning. The results seem to suggest that both learning systems are recruited, at least to some extent, when action-feedback and stimulus-feedback associations are considered simultaneously.