Although we sometimes refer to sadness as “the blues,” depression can often feel more like a state of unrelieved gray. Some recent research has found that in the retinas of depressed people, the response to black/white contrasts was notably lower than in healthy people. This backs up an earlier study which found that depressed people had a harder time detecting differences between black and white (I’m assuming they were talking about fairly subtle differences). The effect of viewing a more monotone world seems obvious (what a downer), but it’s not clear to me how to interpret it. This seems like evidence of a glitch in the sensory equipment that’s associated with depression. On the other hand, some researchers think that depression might be (or might have been) an adaptive withdrawal from the world; in that case, the change in vision might be part of the mechanism that causes that withdrawal. At any rate, the effect was big enough that they could tell most of the depressed people from the healthy ones.
You can read more about the work in this article from Science Daily. The full citation is:
Seeing Gray When Feeling Blue? Depression Can Be Measured in the Eye of the Diseased, by Emanuel Bubl, Elena Kern, Dieter Ebert, Michael Bach, Ludger Tebartz van Elst. Biological Psychiatry 68(2): 205-208 (15 July 2010).