⁵A very similar account has been proposed for the simple emotion of sadness by Oatley and Johnson-Laird (1987). The difference is mainly in the time scales involved, since depression is by definition much more long-term than sadness. Sadness in its turn could be seen as a frustration or disappointment signal which is particularly strong and relatively long-lasting, but the terminology here is not very well-defined. A related computational account of depression focusing on the concept of learned helplessness is given by Huys and Dayan (2009).