Objective detection and subject valuation of reward
When we perform an action and we get a reward, we are likely to repeat that action. If there is a negative outcome, we won't do it again. The question is, what exactly counts as a reward. If you get 10$ present for Christmas, that is cool. But if all other family members get presents that are worth 100$, you might not really enjoy your "reward". In this example, the gift you received is an objective reward, you received something positive you did not have before. At the same time it is a subjective punishment, because you are worse off than everyone around you.
For our brain it is important to process both types of feedback. In survival sitations an object reward promotes survival, even if it is subjectively not ideal. However, a fair society promotes community and thus subjective rewards and punishments needs to be established as well. Previous studies using EEG (read more about EEG in the Neuroscience Methods section) have identified two components related to reward and punishment processing. However, objective and subjective aspects were not investigated.
Methods
Participants had to decide which of two vases was most expensive. After their decision they received feedback on how many points they earned. The correct answer led to the most points. This means that this was subjectively always better than the wrong answer. However, in an objective sense they could still receive minus points.
For example, in the first trial you make the correct choice. You receive -10 points, but for the other option you would have received -50 points. This reflects an object punishment, because you lose points, but a subjective reward because it is better than the other option. In the second trial you make the wrong choice and you receive 30 points, but the other option would have given you 70 points. This is an objective reward, you gained points, but a subjective punishment because the other option was better.
As such our experiment had trials with all options: objective and subjective reward, subjective reward but objective punishment, objective reward but subjective punishment, and objective and subjective punishment.
We looked at the EEG when participants received feedback. After feedback typically two EEG waves, so-called components, are observed. A positive wave after 200 ms (P200), and one after 300 ms (P300). We investigated how they relate to objective and subjective outcomes.
Results
We found that both EEG signals, the P200 and P300, are related to reward and punishment feedback. For both components, the signals were different when a reward or when a punishment was received.
The P200 signal differences, were opposite for subjective and objective outcomes. Whereas a subjective reward resulted in a big P200, so did objective punishments. A small P200 was observed for subjective punishment and objective reward.
For the P300 a different pattern was observed. Here both subjective and objective rewards resulted in big amplitudes, whereas subjective and objective punishments led to a small P300.
Discussion
Although the two EEG components P200 and P300 are both related to processing reward and punishment feedback, they do so in different ways. The P200 processes subjective and objective outcomes in opposing ways. Thus this component most likely relates to brain processes that are involved with giving an outcome personal value. Similar to the Christmas example, described in the introduction. However, the P300 does not make a distinction between objective and subject outcomes. Only between good versus bad outcomes. So this component likely reflects brain processes related to feedback that is most optimal for you. That is, feedback which will prompt you to repeat behavior, in case of a reward, versus feedback that will prompt you to do something different, in case of a punishment. As such, this P300 might be more important for learning from positive and negative outcomes. This is in line with other studies that have related the P300 to learning.
Source
Wischnewski & Schutter (2018). Dissociating absolute and relative reward- and punishment-related electrocortical processing: An event-related potential study. Int J Psychophysiol, 126, 13-19. https://doi.org/10.1016/j.ijpsycho.2018.02.010