from deciding whether our clothes match to

determining whether a shady character

in the street is a threat.

Such decisions aren't based on hard-and-fast rules,

a new study reveals.

Instead, our concept of “threat” -

and even of the color “blue” – is all relative.

To make the find, researchers showed non color-blind

participants a series of 1000 dots ranging

from very blue to very purple, and asked them

to judge whether each dot was blue.

For the first 200 trials,

participants saw an equal number of dots

from the blue and purple parts of the spectrum,

but then the prevalence of blue dots gradually

decreased to just a fraction of what it was before.

By the end of the study,

participants' interpretation of the colors had changed:

dots that they had thought were purple

in the first set of trials they now classified as blue

That is, their concept of the color blue

had expanded to also include shades of purple.

Even when the researchers forewarned participants

that blue dots would become rarer and promised

them money if they kept their judgments consistent,

the same shift occurred.

And the team found similar results in

more complex versions of the task, where participants

had to judge whether a face was threatening

or if a research proposal was ethical.

When threatening faces became less common,

people started to consider previously benign

examples as posing a threat.

These results could explain why so many people

tend to be pessimistic about the state of the world.

As common problems become rare, previously

minor issues start to seem much more problematic.