and we are embedded in a very large cosmos,

and the fact is that we are not very good at understanding reality

at either of those scales,

and that's because our brains

haven't evolved to understand the world at that scale.

Instead, we're trapped on this very thin slice of perception

right in the middle.

But it gets strange, because even at that slice of reality that we call home,

we're not seeing most of the action that's going on.

So take the colors of our world.

This is light waves, electromagnetic radiation that bounces off objects

and it hits specialized receptors in the back of our eyes.

But we're not seeing all the waves out there.

In fact, what we see

is less than a 10 trillionth of what's out there.

So you have radio waves and microwaves

and X-rays and gamma rays passing through your body right now

and you're completely unaware of it,

because you don't come with the proper biological receptors

for picking it up.

There are thousands of cell phone conversations

passing through you right now,

and you're utterly blind to it.

Now, it's not that these things are inherently unseeable.

Snakes include some infrared in their reality,

and honeybees include ultraviolet in their view of the world,

and of course we build machines in the dashboards of our cars

to pick up on signals in the radio frequency range,

and we built machines in hospitals to pick up on the X-ray range.

But you can't sense any of those by yourself,

at least not yet,

because you don't come equipped with the proper sensors.

Now, what this means is that our experience of reality

is constrained by our biology,

and that goes against the common sense notion

that our eyes and our ears and our fingertips

are just picking up the objective reality that's out there.

Instead, our brains are sampling just a little bit of the world.

Now, across the animal kingdom,

different animals pick up on different parts of reality.

So in the blind and deaf world of the tick,

the important signals are temperature and butyric acid;

in the world of the black ghost knifefish,

its sensory world is lavishly colored by electrical fields;

and for the echolocating bat,

its reality is constructed out of air compression waves.

That's the slice of their ecosystem that they can pick up on,

and we have a word for this in science.

It's called the umwelt,

which is the German word for the surrounding world.

Now, presumably, every animal assumes

that its umwelt is the entire objective reality out there,

because why would you ever stop to imagine

that there's something beyond what we can sense.

Instead, what we all do is we accept reality

as it's presented to us.

Let's do a consciousness-raiser on this.

Imagine that you are a bloodhound dog.

Your whole world is about smelling.

You've got a long snout that has 200 million scent receptors in it,

and you have wet nostrils that attract and trap scent molecules,

and your nostrils even have slits so you can take big nosefuls of air.

Everything is about smell for you.

So one day, you stop in your tracks with a revelation.

You look at your human owner and you think,

"What is it like to have the pitiful, impoverished nose of a human?

(Laughter)

What is it like when you take a feeble little noseful of air?

How can you not know that there's a cat 100 yards away,

or that your neighbor was on this very spot six hours ago?"

(Laughter)

So because we're humans,

we've never experienced that world of smell,

so we don't miss it,

because we are firmly settled into our umwelt.

But the question is, do we have to be stuck there?

So as a neuroscientist, I'm interested in the way that technology

might expand our umwelt,

and how that's going to change the experience of being human.

So we already know that we can marry our technology to our biology,

because there are hundreds of thousands of people walking around

with artificial hearing and artificial vision.

So the way this works is, you take a microphone and you digitize the signal,

and you put an electrode strip directly into the inner ear.

Or, with the retinal implant, you take a camera

and you digitize the signal, and then you plug an electrode grid

directly into the optic nerve.

And as recently as 15 years ago,

there were a lot of scientists who thought these technologies wouldn't work.

Why? It's because these technologies speak the language of Silicon Valley,

and it's not exactly the same dialect as our natural biological sense organs.

But the fact is that it works;

the brain figures out how to use the signals just fine.

Now, how do we understand that?

Well, here's the big secret:

Your brain is not hearing or seeing any of this.

Your brain is locked in a vault of silence and darkness inside your skull.

All it ever sees are electrochemical signals

that come in along different data cables,

and this is all it has to work with, and nothing more.

Now, amazingly,

the brain is really good at taking in these signals

and extracting patterns and assigning meaning,

so that it takes this inner cosmos and puts together a story

of this, your subjective world.

But here's the key point:

Your brain doesn't know, and it doesn't care,

where it gets the data from.

Whatever information comes in, it just figures out what to do with it.

And this is a very efficient kind of machine.

It's essentially a general purpose computing device,

and it just takes in everything

and figures out what it's going to do with it,

and that, I think, frees up Mother Nature

to tinker around with different sorts of input channels.

So I call this the P.H. model of evolution,

and I don't want to get too technical here,

but P.H. stands for Potato Head,

and I use this name to emphasize that all these sensors

that we know and love, like our eyes and our ears and our fingertips,

these are merely peripheral plug-and-play devices:

You stick them in, and you're good to go.

The brain figures out what to do with the data that comes in.

And when you look across the animal kingdom,

you find lots of peripheral devices.

So snakes have heat pits with which to detect infrared,

and the ghost knifefish has electroreceptors,

and the star-nosed mole has this appendage

with 22 fingers on it

with which it feels around and constructs a 3D model of the world,

and many birds have magnetite so they can orient

to the magnetic field of the planet.

So what this means is that nature doesn't have to continually

redesign the brain.

Instead, with the principles of brain operation established,

all nature has to worry about is designing new peripherals.

Okay. So what this means is this:

The lesson that surfaces

is that there's nothing really special or fundamental

about the biology that we come to the table with.

It's just what we have inherited

from a complex road of evolution.

But it's not what we have to stick with,

and our best proof of principle of this

comes from what's called sensory substitution.

And that refers to feeding information into the brain

via unusual sensory channels,

and the brain just figures out what to do with it.

Now, that might sound speculative,

but the first paper demonstrating this was published in the journal Nature in 1969.

So a scientist named Paul Bach-y-Rita

put blind people in a modified dental chair,

and he set up a video feed,

and he put something in front of the camera,

and then you would feel that

poked into your back with a grid of solenoids.

So if you wiggle a coffee cup in front of the camera,

you're feeling that in your back,

and amazingly, blind people got pretty good

at being able to determine what was in front of the camera

just by feeling it in the small of their back.

Now, there have been many modern incarnations of this.

The sonic glasses take a video feed right in front of you

and turn that into a sonic landscape,

so as things move around, and get closer and farther,

it sounds like "Bzz, bzz, bzz."

It sounds like a cacophony,

but after several weeks, blind people start getting pretty good

at understanding what's in front of them

just based on what they're hearing.

And it doesn't have to be through the ears:

this system uses an electrotactile grid on the forehead,

so whatever's in front of the video feed, you're feeling it on your forehead.

Why the forehead? Because you're not using it for much else.

The most modern incarnation is called the brainport,

and this is a little electrogrid that sits on your tongue,

and the video feed gets turned into these little electrotactile signals,

and blind people get so good at using this that they can throw a ball into a basket,

or they can navigate complex obstacle courses.

They can come to see through their tongue.

Now, that sounds completely insane, right?

But remember, all vision ever is

is electrochemical signals coursing around in your brain.

Your brain doesn't know where the signals come from.

It just figures out what to do with them.

So my interest in my lab is sensory substitution for the deaf,

and this is a project I've undertaken

with a graduate student in my lab, Scott Novich,

who is spearheading this for his thesis.

And here is what we wanted to do:

we wanted to make it so that sound from the world gets converted

in some way so that a deaf person can understand what is being said.

And we wanted to do this, given the power and ubiquity of portable computing,

we wanted to make sure that this would run on cell phones and tablets,

and also we wanted to make this a wearable,

something that you could wear under your clothing.

So here's the concept.

So as I'm speaking, my sound is getting captured by the tablet,

and then it's getting mapped onto a vest that's covered in vibratory motors,

just like the motors in your cell phone.

So as I'm speaking,

the sound is getting translated to a pattern of vibration on the vest.

Now, this is not just conceptual:

this tablet is transmitting Bluetooth, and I'm wearing the vest right now.

So as I'm speaking -- (Applause) --

the sound is getting translated into dynamic patterns of vibration.

I'm feeling the sonic world around me.

So, we've been testing this with deaf people now,

and it turns out that after just a little bit of time,

people can start feeling, they can start understanding

the language of the vest.

So this is Jonathan. He's 37 years old. He has a master's degree.

He was born profoundly deaf,

which means that there's a part of his umwelt that's unavailable to him.

So we had Jonathan train with the vest for four days, two hours a day,

and here he is on the fifth day.

Scott Novich: You.

David Eagleman: So Scott says a word, Jonathan feels it on the vest,

and he writes it on the board.

SN: Where. Where.

DE: Jonathan is able to translate this complicated pattern of vibrations

into an understanding of what's being said.

SN: Touch. Touch.

DE: Now, he's not doing this --

(Applause) --

Jonathan is not doing this consciously, because the patterns are too complicated,

but his brain is starting to unlock the pattern that allows it to figure out

what the data mean,

and our expectation is that, after wearing this for about three months,

he will have a direct perceptual experience of hearing

in the same way that when a blind person passes a finger over braille,

the meaning comes directly off the page without any conscious intervention at all.

Now, this technology has the potential to be a game-changer,

because the only other solution for deafness is a cochlear implant,

and that requires an invasive surgery.

And this can be built for 40 times cheaper than a cochlear implant,

which opens up this technology globally, even for the poorest countries.

Now, we've been very encouraged by our results with sensory substitution,

but what we've been thinking a lot about is sensory addition.

How could we use a technology like this to add a completely new kind of sense,

to expand the human umvelt?

For example, could we feed real-time data from the Internet

directly into somebody's brain,

and can they develop a direct perceptual experience?

So here's an experiment we're doing in the lab.

A subject is feeling a real-time streaming feed from the Net of data

for five seconds.

Then, two buttons appear, and he has to make a choice.