²⁸The RPE formalism could also be interpreted as providing another baseline mechanism, by looking at the change of state-values. Going to a state which has a lower value than the current state, without obtaining any reward, does produce suffering according to the definition of RPE above, as explained in footnotes 20 and 21 in this chapter. From this viewpoint, RPE uses the current state-value as the baseline defining what is “low”, looking at the total expected future reward. See also footnote 15 on different possibilities of defining the baseline as “expectation”. Chapters 6 and 9 will further discuss how such expectations can operate on different time scales, and we will see that a long-term lack of rewards can indeed be considered frustration when looking at a longer time scale.