It's common knowledge now that depression is linked to the way our brains are wired, but a new study out of Finland has shown that a depressive episode can literally change the way we see the world.
Scientists at the University of Helsinki tested how participants with and without depression viewed an illusion they were presented with: two identical squares imposed on different backgrounds.
In one test, the two squares of the same colour were placed inside two larger squares, with the larger square in shape A significantly darker than that in B.
Most participants were able to pick the difference, despite their mental health status.
In a second test, participants were presented with two more identical squares (C and D) which contained vertical lines. While C was set against a matching background, D was imposed against horizontal lines.
This means the lines in square D are usually perceived as much bolder because of the contrast. But researchers found that depressed patients generally struggled to see this.
"What came as a surprise was that depressed patients perceived the contrast of the images shown differently from non-depressed individuals," says psychologist Viljami Salmela.
The results of the research published in the Journal of Psychiatry and Neuroscience this week suggest there is "altered cortical processing of visual contrast" during a major depressive episode.
"Because contrast suppression is orientation-specific and relies on cortical processing, our results suggest that people experiencing a major depressive episode have normal retinal processing but altered cortical contrast normalization," the journal article reads.
More research will be needed on exactly why this occurs, the scientists added.