Take a look at these schematic faces:
Just a few simple changes to the mouth and eyebrows can create faces depicting a wide array of emotions. Face 1, for example, is clearly quite happy, and face 12 is sad. Face 7 is obviously angry. But what about face 4? Embarrassed? Happy but sleepy?
Perhaps your own emotion at the time you look at the faces might affect your understanding of the emotions the faces convey, especially when the emotional state depicted is unclear. Perhaps people suffering from clinical depression are stuck in a sort of infinite feedback loop: every face they see seems sadder than it really is, causing more negative emotions, worsening the depression.
Working with healthy college students, a team led by Antoinette L. Bouhuys manipulated their emotional states before asking them to rate the emotions depicted in pictures.
Fifteen students listened to happy music (Delibes’ “Coppélia”) for seven minutes, then quickly reported on their emotional state, then rated six of the faces for how much they depicted each of 8 different emotions (rejection, invitation, happiness, sadness, anger fear, disgust, and surprise). Then they reported their own emotional state again. The procedure (including the music) was repeated again for the remaining six faces. The other fifteen students listened to sad music (Sibelius’ “Swan of Tuonela”), following the same procedure.
The researchers were indeed successful at manipulating emotions, especially with the negative music:
So did students rate the pictures differently when they themselves were experiencing these different emotions? It depends on the type of face they were rating. For most of the faces, there was no difference in the ratings, but for a few types, a pattern emerged:
The students who had heard the depressing music rated ambiguous, less intense faces significantly higher for rejection and sadness than those who heard the happy music. They rated clear, less intense faces significantly higher in fear and lower in invitation / elation than those who listened to the happy music.
So overall people who are feeling more depressed are likely to see more negative emotions and less positive emotions, even in schematic faces, especially when the faces are ambiguous or less intense.
Bouhuys et al. suggest that this phenomenon might make clinical depression self-reinforcing. Depressed people see more negativity even in benign facial expressions, which in turn leads to more depressed emotions.
Bouhuys, A.L., Bloem, G.M., & Groothuis, T.G.G. (1995). Induction of depressed and elated mood by music influences the perception of facial emotional expressions in healthy subjects. Journal of Affective Disorders, 33, 215-226.