Meanwhile owls will be more likely to see it as blue.

Their brain will assume it's the kind of incandescent light they see inside at night.

And under that kind of light, the dress is blue.

He tested this theory with a sample of about 1,000 people, many of whom he recruited from an article he published in Slate.

Okay, back to Pascal.

What we found is the more you identify as a night owl, the more black and blue you think that image is--it's a dose-dependent effect.

These are very, very strong effects.

But still--chronotype is just a proxy for the thing Pascal was really trying to measure, which was what assumptions your brain made when viewing the image. He needed to go deeper.

The next step was to replicate the result in a new context to show that it wasn't a one-off fluke and what you saw really did come down to assumptions your brain made about ambiguity.

So here's what I thought, "What's the principle here?" So first of all, we need to introduce uncertainty.

We need to take an image, an image that could be any color, and put it under artificial lighting and take all context cues away.

So you're creating another condition where it's not immediately obvious what the colors should be.

My collaborator, Michael Karlovich, came up with the idea of using Crocs and socks.

Ah, Crocs--those funny plastic shoes that come in a whole range of colors. There's no default color for them.

Crocs can be any color really. I think there's something like 28 different kinds of Crocs, yes?

Okay, so I've got the Crocs and socks image up on my computer screen right now.

The socks are almost like a neon green. And the Crocs are a very bland color--maybe gray? I guess I'd call them beige.

Great. Now here's the thing, here's the crazy thing...so we were able to do the following.

So, first of all, I have the…it's too bad, if I had known that…I would bring the Crocs.

I have the Crocs. The Crocs…the Crocs are pink-undeniably they are just as pink as the blue dress is blue.

Really?

If you put the Crocs under--on a black background, and we did this in my attic--we blacked out my attic, and then you illuminate the Crocs ... and you put them under green light, that will add up to gray.

And at that point, it's unclear if you're looking at gray Crocs on a black background under normal light or pink Crocs under green light.

So it's just like the dress--what you see depends on what you assume about the lighting.

But there's one dead giveaway. It's not just the Crocs.

It's the Crocs and the socks. Here's the kicker: when I was young, socks like that were always white--always, always, always.

So if I shine green light on these pink Crocs, even though they look gray, I will know the socks will look green, subjectively.

But I know that the socks are white, so I can mentally subtract the green from the socks to then color calibrate.

Wait, the socks are white? Oh, wow! This is so bizarre!

As you were talking about the white socks, I had this immediate recognition that, "oh, these are those white tube socks that everyone used to wear when I was a kid."

As that recognition clicked, the Crocs turned pink.

It was almost instantaneous. It's so wild. I've never experienced anything like this.

We asked people, "What do you see the Crocs as? And what do you see the socks as?"

And to make a long story short, and I have to send you the paper on this…the people who saw the socks as white and who are sure about this ... 80 percent or something like that see the Crocs as pink, even though they actually look gray at face value.

So what's happening here is that people who assumed the socks could be green, which is the color they objectively look, just based on wavelength, see the Crocs as gray or beige.

But people who saw Bob--that is, they knew the socks were white because they're always white--they color corrected and saw the Crocs as their true color, which is pink.

Once again, your brain is processing ambiguity by relying on your prior assumptions, and you don't even realize it.

Pascal, do you think there are larger lessons we can take away from this?

Well, I think the biggest lesson is: don't be so sure of yourself.

Just because you're sure does not mean you're right. This uncertainty is hidden from you, yes?

Oh, I was absolutely certain the dress was white. And when I heard other people saying they saw blue, I felt incredulous.

But you're saying that maybe next time, instead of immediately assuming that everyone else is denying reality, I should be more open to the idea that I am the one who is wrong?

Your brain doesn't say, "I have absolutely no idea...." It doesn't say that.

Your brain tells you, "I think it's white and gold." That's it.

It doesn't flag to you, "Oh, and by the way, I made a guess here."

Your brain is just making a judgment call, and you never even realize how uncertain it was in the first place.

Yeah. It's like a game show. It's our best guess; it's our final answer. But it doesn't tell you that-that it made a guess.

So if we're not careful, we can end up with a bunch of ignorant overconfidence.

I think we need a culture of awareness and intellectual modesty that counteracts this evolutionary tendency to jump to conclusions and then commit to them.

We think that what we see represents stone-cold reality.

And that can be a problem because it turns out that we have a natural blind spot for the ways we might misinterpret reality.

Psychologists have a term for this: "naive realism" is the assumption that the way we see the world is the way it really is. We are blind to our blind spots.

Pascal's experiments are on visual perception, but they highlight a concept that's true in many aspects of science: the uncertainty we don't perceive can warp our view.