Medial frontal brain potentials following feedback during probabilistic learning.

Abstract

Over 10 years after its discovery, controversy still abounds over the functional significance of an event-related potential known as the Error-Related Negativity (ERN). A number of theories (and models constructed from them) have been proposed in an attempt to explain it, including an error detection theory (the mismatch hypothesis), a conflict-monitoring theory, a reinforcement learning theory and an affective processing theory. These theories have received mixed empirical support and none stands out as more compelling than the others. The reinforcement learning theory of the ERN (RL-ERN) provides the latest endeavor to derive an explicit model of the functional significance of the ERN. This is an innovative and sophisticated model of the ERN that generates a number of new predictions about the effects of experimental manipulations on the ERN. One key prediction of the RL-ERN model is that the amplitude of the ERN will be larger when an event is worse than expected. A series of experiments was performed to test this prediction and assess the ERN over the course of learning. The tasks required participants to learn probabilistic associations between either stimuli and outcomes, or stimuli and responses. Participants' accuracy and their confidence in their performance were measured in order to assess their expectations explicitly. While some results were consistent with the RL-ERN model, others provided little support for it; in particular, the ERN was not found to be larger following unexpected error feedback (i.e., an event that is worse than expected), relative to expected error feedback (i.e., an event that is expected). In fact, the results suggest that the ERN is largest early in learning and when the association has not been learnt, suggesting it is largest before expectations can be developed; this has implications for other theories of the ERN as well as the RL-ERN. On the basis of these results and existing literature, an affective, or motivational, function is ascribed to the ERN as part of a more integrated system, involved in the processing of motivationally significant stimuli, whose functions include allocation of attention, arousal, preparation for action and learning.