(bright music) - Okay, there's something I want you to visualize, with your mind's eye.

So if it helps, perhaps close your eyes.

In your mind, I want you to imagine the sky.

It's really blue, and suddenly it becomes brighter.

Then a rainbow appears.

You turn your head and another rainbow appears.

It's a double rainbow.

It's so vivid and intense.

Now, how clear is this mental image?

Can you see each color in the rainbow?

Can you picture a bird flying in front of it?

When some people are asked to picture something, with their mind's eye, they just can't.

Hey Andy, it's Vanessa.

How are you?

- I'm quite well, yourself?

- I'm well, thank you so much.

- Now, Andy believes he has aphantasia, a condition where you have little, or no mental imagery.

It's been referred to as blind imagination, or having a blind mind's eye.

- I asked Andy to visualize his breakfast table, and well, his brain uses different strategies to imagine these visual problems.

- It's more akin to a word cloud, a long list of adjectives that describe the table.

If you were to take me out of my kitchen, and ask me to describe my dining room table, I can tell you things about my dining room table, but if I wasn't told the word was imagine, like image, I wouldn't use visual metaphors.

When I imagine a coffee table, I'm more imagining concepts about coffee tables.

- Now I learned about aphantasia a few weeks ago, when Andy commented on my last video, - "I don't have any visual memory or imagination."

- And people commenting on articles, was exactly how this condition came to be studied in the first place.

- Now we've known that some people have a blind imagination, since the 1880s.

When Sir Francis Galton asked people to visualize things about their breakfast table.

One of the subjects, actually Charles Darwin said it was as distinct as if I had the photos before me.

But a few people couldn't visualize the table at all.

Fast forward to the early 2000s.

When urologists at the University of Exeter encountered patient MX, a Scottish man who lost his ability to visualize things after surgery.

When MX was in an fMRI machine, researchers showed him a picture of then Prime Minister, Tony Blair, and asked questions like, does he have large ears?

Well, yes.

As expected, they saw normal activity in his visual areas.

Next, they asked him to imagine Blair's face.

They expected to see similar brain activity, but instead many areas were active.

Including those used for semantic retrieval.

MX was trying to imagine a face but in a non-visual way, using words, instead of images.

When that research was published in 2010, Carl Zimmer wrote this article for Discover Magazine.

And email started rolling in from people who experienced the same thing.

- Email - Some since both, the blind imagination of this group of emailers was the focus of a new paper published by the same researchers in 2015, who officially named this Aphantasia.

They found the majority of the group couldn't conjure up a mental image at will, but they still had flashes of vision.

Perhaps in dreams.

Most said they had some trouble remembering past events, and most discovered their Aphantasia in their teens or 20s.

- Like I'm a grown-up.

And I didn't realize until recently that visualize like terms like mind's eye.

I thought they were euphemisms like maybe a quirk of the English language.

It felt like not realizing that I was color blind.

- Right, wow.

- From here Carl Zimmer a again, wrote about this new paper.

Sasha posted a video on it, and the researchers received close to a thousand emails from people who just heard of Aphantasia and believed they haven't similar to Andy.

As the lead researcher put it a testing it to the popular interest in relative obscurity of the fascinating variation of human experience.

But why is the human experience so varied?

Well, we don't know, but scientists are digging deeper into Aphantasia using brain imaging.

- The story of Aphantasia shows us that we can all contribute to how understanding of how the brain works and how you work.

And we're coming a little bit closer to finding out why some of us can visualize a double rainbow in the first place.

(soft music) - What does this mean?

Oh.