Depression changes people's feelings. It might also change their thoughts, or more specifically, it may make them pay more attention to these thoughts. Psychologists have noticed that a particular word game, a game that evokes the Stroop Effect, seems to have a peculiar impact on people with depression.
We think that the ability to read is a complicated, artificial process, but when's the last time you've seen a sign, in your native language, that you've chosen not to read? The Stroop Test shows how deep the ability to read runs through us.