April 17, 2023 • 53 mins
Do you see blue the same way I do on the inside? Why do some people think the northern lights make noise? Why do you think the low note on the piano is larger, and the high note brighter? Join Eagleman on a wild ride into the world of synesthesia, a topic his neuroscience laboratory has pioneered for years.
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Speaker 1 (00:06):
Why do some people think that the Northern lights make
noise and other people say that that's impossible. And why
did Pythagoras think that numbers had colors and personality? And
what does any of that have to do with creators
like Vladimir Nabokoff and Billie Eilish, And why do you
think that a high note on the piano is brighter
(00:29):
than a low note. Welcome to Inner Cosmos with me,
David Eagleman. I'm a neuroscientist and an author at Stanford University,
and I've spent my whole career studying the intersection between
how the brain works and how we experience life. On
(00:55):
today's episode, we're going to talk about how we can
all experience reality a little bit differently. Okay, so this
story begins in the early nineteen thirties. You've heard about
the Northern lights, or maybe you've even seen them in person.
They're these rippling rivers of green blue light in the sky.
(01:15):
But here's the really strange part. About one hundred years
ago some people started to make the claim that the
northern lights make noise. In nineteen thirty one, in the
journal Nature, a scientist named Harold's Fairdrop wrote a short
paper that he called Audibility of the Aurora polaris, and
(01:35):
he wrote, quote, it cannot be doubted that many persons
have heard a distinct sound when watching a brilliant display
of aurora. Communications regarding the auroral sound appear now and then,
and recently.
Speaker 2 (01:52):
Mister J. H.
Speaker 1 (01:53):
Johnson has collected a great number of reports on the
auroral sound in his pamphlet concern the Aurora borealis. Then,
in nineteen thirty three in the journal Science, someone named
Clark Garber wrote another letter on the audibility of the
Aurora borealis, and Garber wrote quote, some scientists have claimed
(02:15):
with much positiveness that the aurora emits no audible sounds.
In my own mind, there can be no doubt left
as to the audibility of certain types of aurora, for
I have heard them under conditions when no other sound
could have been interpreted as such, for no other sounds
were present. And he goes on to say that he
(02:37):
first heard about the possibility that the aurora makes sounds
from the eskimos, and he says he was skeptical at first,
but then he experienced this sound himself. Now I stumbled
on these papers a few years ago, and I was
surprised because the problem is that it's not scientifically possible
for the Aurora to make sound. The Northern Lights happen
(03:01):
because photons from the Sun are banging into gases in
the Earth's upper atmosphere, and that causes all that amazing light.
But those collisions are happening eighty kilometers up in the sky,
which means that even if there were sound, it would
take about four minutes for that sound to get down here.
And yet people who claim to hear the sound say
(03:24):
they see it happening in lockstep with the lights. And
more importantly, for sound to travel it needs a medium
like air, and that's because sound moves as compression of
the air. In other words, molecules in the air get
pushed closer together and farther apart, and that's what a
sound wave is. But at the altitude where the Northern
(03:45):
Lights come into being, the atmosphere is essentially a vacuum.
Speaker 2 (03:50):
So this means there's probably no.
Speaker 1 (03:52):
Sound happening even up there, and if there were, it
couldn't get all.
Speaker 2 (03:56):
The way to us until four minutes later.
Speaker 1 (03:58):
So this became a top of debate because as time
went on, thousands of Arctic explorers listened carefully for these
sounds but didn't hear anything. So this idea of the
northern lights making noise came to be understood as a superstition.
So what was happening here? Were some people simply lying
(04:20):
in scientific journals It's happened before, But it seems that
some people really believed and still believe, the lights make sound,
even though the physics don't seem to allow that. So
worse Ferdrup and Garber lying, were they looking for attention
that they somehow have better hearing? Even today? This is
(04:41):
contentious in geophysics. Some people argue from their personal experience
that it happens, and others point out that it simply can't.
To unpack this mystery, let's jump back even farther back
another twenty five hundred years to Pythagoras. Pythagoras was one
(05:01):
of Greece's most famous philosophers, and he massively influenced the
trajectory of Western thought through his religious teachings his political teachings.
In part this was due to his influence on Plato
and Aristotle. But you've probably heard of Pythagoras because of
his love of numbers. He loved geometry and theories about
(05:24):
instrument tuning and the theory of proportions, and you'll probably
remember the Pythagorean theorem from school in a right triangle,
A squared plus B squared equals C squared. But there
was something very odd about Pythagoras's relationship with numbers. I'm
going to quote from the Yale historian Robert Brumbaugh, who
(05:47):
notes that for Pythagoras quote, each number had its own personality,
masculine or feminine, perfect or incomplete, beautiful or ugly. For Pythagoras,
ten was the very best number. This feeling modern mathematics
has deliberately eliminated, but we still find overtones of it
(06:11):
in fiction and poetry. Now, how could numbers have gender
and personality? Did Pythagoras have fundamental insight about numbers that
the rest of us couldn't see? Or was he making
up stuff to impress his followers, or was he mentally
(06:32):
ill or taking drugs. The way that he personified numbers
is traditionally discussed as an interesting oddity, or occasionally you'll
find numerologists who cite Pythagoras's view as evidence that he
had a cosmic insight into the true natures of numbers.
I've seen websites that springboard from Pythagoras's number personalities to
(06:56):
sell new age models of the nature of the universe.
But most people don't believe that the number five has
a gender or a personality. So what was going on
here and what does this have to do with the
scientists who claim to hear sounds from the Northern Lights.
The answer to both these mysteries is related to something
(07:16):
I'm going to discuss a lot across many episodes of
this podcast, and that is the difference in people's internal worlds.
We all like to believe that our experience of the
world is the same as everyone else's. But the key
to unlocking the mystery of the Northern Lights or Pythagoras's
view of numbers is to understand that people can have
(07:39):
very different realities on the inside. The interesting part, as
we'll see, is that we accept the reality presented to us.
Your brain constructs a story about what's going on out there,
and you accept that as your reality. So imagine I
showed you a picture of a crowd of people. If
(08:00):
you're color blind, all you see are shades of gray.
If you're not colorblind, you see it in full color.
But either way, that's the reality that you know. And
we now know that a very tiny fraction of the
female population doesn't just have three types of color photoreceptors
in their eyes, but they have four types because of
(08:22):
a mutation, and as a result, they perceive colors that
the rest of us can't even imagine. Their reality is different.
So the key is we accept whatever reality our brains
serve up to us. Okay, So this all leads to
a very old philosophical question which I think everyone has
(08:44):
asked at some point in their lives. How do you
know that what I see as blue is what you
see as blue? My parents taught me to call that
thing blue, and your parents taught you to call it blue.
Speaker 2 (08:59):
Two. But inside your.
Speaker 1 (09:01):
Head and inside my head, it might be a different experience.
Speaker 2 (09:05):
Right.
Speaker 1 (09:06):
I might be seeing it as what you would think
of as green, But it doesn't matter, and we'd never
know as long as we can transact in the outside world.
In other words, if I say, hey, can you pass
me that blue thing, and we both call it blue,
then the word suffices, even if we're having a different
(09:26):
internal experience and it turns out. The situation might be
even worse than that. It may be that what I
call vision and what you call vision are totally different.
I might see the world completely upside down from the
way that you see the world, and it wouldn't matter
as long as we can agree on things out there,
and I can throw a ball and you can catch it.
(09:48):
So what my colleagues and I have worked on for
years is taking this question or we having different lives
on the inside and elevating that from the realm of
phys sophical speculation to actual scientific experiment. And one way
to get at that this was something my lab is
studied for fifteen years called sinnesthesia. Synesthesia is a condition
(10:14):
in which one person might be seeing reality a little
bit differently from another. So you know the word anesthesia,
that means no feeling. Synesthesia means joined feeling. It's a
blending of the senses. Now, there are many forms of synesthesia,
and one of the most common is where a person
(10:36):
looks at numbers or letters and that triggers an internal
experience of color. So for a given synesthete, her eight
might trigger the experience of blue. She still sees the
number eight on the page. There if I were to
write eight with black ink on a white page, she'd
say that she can see the number, but seeing the
(10:57):
number eight triggers a blue experience, an internal experience of blue.
And it's just self evidently true for her that eight
and blue are connected. Now this isn't just a memorized
thing that she says, but it's an actual experience. And
for her, maybe five is yellow, and Saturday is orange,
(11:20):
and November is purple and so on. Now, the first
thing to note is that sequences that we learn, like
letters and numbers and weekdays and months, these are drilled
into the brain really deeply. They're known in the field
as overlearned sequences, and these are the things that trigger synesthesia.
(11:42):
And interestingly, this often goes beyond color in when flavor
of synesthesia, sequences come to have gender and personality and
other qualities. So one cynesthete describes the number three as
a vain, elitist girl, while seven is a shy, wimpy boy.
(12:05):
This same cynisthe described by my colleague Sean Day. She
also noted that she doesn't like certain number combinations, like
ninety four.
Speaker 2 (12:14):
That quote result.
Speaker 1 (12:16):
In putting four, which is a plain but decent, hardworking
older woman and nine together as they greatly dislike each
other and do not get along well. And this is
what was going on with Pythagoras. He had this not
uncommon form of synesthesia, but his followers didn't know this,
(12:36):
so they presumably thought he was tapped into some cosmic
truth about numbers. He obviously liked numbers, but that doesn't
mean he had access to some deeper significance that others didn't.
How do we know that, Because each person with this
particular type of synesthesia has a different association between a
(12:57):
particular number and a gender personality. So you might think
three is male and kind, and someone else might think
three is female and a bit of a comic, and
so on. There is no right answer. So we're gonna
come back to this in a moment, But first I
want to tell you about some other forms of synesthesia.
(13:18):
It's not just colors or genders or personalities triggered by
overlearned sequences. There's also a flavor of synesthesia in which
what you hear causes a visual experience. So you might
listen to music and that causes you to see moving
shapes or colors. In my book, Wednesday's Indigo Blue. I
(13:41):
have a picture of a shape that looks like a
colorful caterpillar, and this is what one synesthete sees. She
actually sees this when her furnace kicks on and goes whoosh.
She has this visual experience that flashes for her. Her
visual system gets tickled by the noise, and senses can
be triggered in the other direction, where something visual leads
(14:05):
to a sound. For some people, when they watch movement
like a swarm of moving birds or an electric sign blinking,
they feel like they hear a sound with it. They
don't see the motion by itself. Their brain imposes sound
on top of that. It's impossible to separate the motion
and the sound. And I've proposed that this is the
(14:27):
solution to the mystery of the Northern lights. It's impossible
from a physics point of view for the lights to
be making synchronized noise. But what is possible is for
a small fraction of the population to be cinnesthetic, such
that when they see the beautiful moving lights, they hear sound.
(14:48):
And because of their assumption that our senses tell us
the truth and that everyone should be having the same experience,
this has led to over a century of debate about
whether the lights make noise or not, because if your
sphare drop or Gerber or any of the others who
hear the sounds, you'll sit down and you'll write a
letter to nature or science and insist that you can
(15:11):
hear it. The important lesson is that we all assume
our senses tell us the truth and that everyone is
tapped into the same reality. But when we realize that's
not necessarily the case, we can take a higher view
on the scientific literature and look at all these papers
(15:31):
going back and forth about whether the northern lights make noise,
and we can understand the game at a different level.
For most people the answer is no, they don't make noise,
and for some it's yes. Beyond the relationship of sound
and vision, there are dozens of forms of synesthesia. My
(15:51):
colleagues and I have found that essentially any sense that
you can imagine can be mixed with another. One form
of synesthesia involves tastes shapes, So when people taste something,
it makes them feel like they're touching something with their fingertips.
So you might take a sip of soup and you
feel something cold and pointy on your fingertips. Or one
(16:13):
guy determines whether his chicken is cooked right this way.
He tastes it and judges by what he's feeling on
his fingertips, is it smooth or glassy or spiky. He
comes to be a good cook that way. And there's
also musical synesthesia. For a lot of people, different notes
of the scale will trigger a color experience. For one
(16:36):
cynisthee that I test in the lab, when she hits
the note A on the piano, that's pink, the note
B is blue. C is goldish white like sunlight. B
is silvery white like moonlight. E is fiery orange, and
(16:58):
so on, So she experiences very specific colors that get
triggered when she hears specific notes. And I know a
professional drum tuner who goes around for all the famous
rock and roll bands and tunes their drums, and he
does it with color, so he can tell if the
drum is a little bit sharp or a little bit
(17:18):
flat by the color that he sees in response to
the sound. Now, not all people with music synesthesia have
their percepts triggered by a pitch a note. For some people,
it's the interval between notes like a chord that matters.
So for one woman, different chords trigger different, very particular
(17:41):
tastes in the mouth. In a paper in the journal Nature,
she reported that she uses these sinnesthetic associations to identify
which chord was just played. And synesthesia can also be
triggered by an instrument's tamber, the way that it sounds.
So when a person hears the music of a violin
versus a tuba, versus a cello versus a flute, the
(18:06):
timbre of the instrument can trigger very different experiences in
terms of colors or visualized shapes or whatever. So two
people might listen to a clarinet playing and that triggers
different internal experiences. One of them sees it as a flat,
horizontal shape with spring like protrusions sticking out, and the
(18:28):
other person sees it as a thick ribbon that's oscillating,
and so on. For different cinisthetes. And beyond shapes or colors,
it can trigger other notions as well, like personalities. One
cinis The reports that the obo is quote profoundly emotional
and thoughtful, with drawn, introspective, and prone to melancholy, while
(18:54):
she describes the flute as quote feminine, sweet, innocent, naive
the personalities of the different instruments. They're not generic, they're
rich and detailed. The triggered perception can also be a
physical sensation, like a physical state of your body. For
one Cyniceitt that I interviewed, different chords make her feel
(19:17):
like her body is in different positions physically, So when
she feels one chord, she feels like she's standing upright
with her feet on the ground, or stepping onto a
stare or soaring in the sky. She happens to be
a professional musician, so when she's memorizing a piece of music,
(19:41):
it's like memorizing a series of dance moves. And there's
one more form, which is likely the most common, around
ten percent of the population experience it. It's when people
perceive sequences like the days of the week or the
months of the year, as though they have a specific
space location in relation to their body, like March is
(20:04):
off here to the left, and April is next to it,
and May is a little bit higher and off next
to that. For every month or a weekday or numbered
things like that, they have a specific spatial location that
the person can identify where it seems to them that
the thing exists. It's just self evidently true to them
(20:25):
that that member of the sequence has that particular spatial location.
This form of synesthesia is not a hallucination. It's not
that you actually see April right there visually.
Speaker 2 (20:37):
It's that it's just obviously true to you.
Speaker 1 (20:40):
That April would occupy that spatial location to you. It
would be like if I asked you to imagine an
apple five feet in front of you. So you're picturing
the apple there and it's got a particular spatial location
with respect to your body, and you can imagine it,
but you're not actually hallucinating it. But if I ask
(21:00):
you where that apple is, that's the spatial location that
it has. A lot of people have this form of
synesthesia for years, like the year nineteen seventy nine has
a specific spot in space and relation to your body,
as does twenty twenty one or twenty fifty seven and
everything in between, and the years sit on this spatial timeline.
(21:22):
The timeline isn't necessarily straight. It can curve or take
sharp turns, and it typically moves with the passing of
each year. Now, what's interesting is that for many cinisthetes,
a year in the past moves behind them, say the
year twenty twenty one. Why because that year has already happened,
so it moves behind you, while a year like twenty
(21:45):
forty two is often the distance ahead of you. But
for other cynisthetes, it's exactly flipped. A year in the
past is in front of them because they already know
what happened in twenty twenty one, but year like twenty
forty two hasn't happened yet, so they don't know anything
about it. It's as invisible to them as an object
(22:07):
that is behind them. I'll just note that another research
group called this form of synesthesia time space synesthesia because
they looked at things like weekdays and months and years
and said, hey, those all have something to do with time.
But I want to emphasize that this is not the
correct way to understand this, because this same spatialization happens
(22:29):
with number lines like one, two, three is over here,
that it takes a right turn here for four through seven,
then eight, nine, ten climb straight up, then eleven through
twenty shoot off in a straight line, and then twenty
one through thirty are stacked above that like that.
Speaker 2 (22:43):
Kind of thing.
Speaker 1 (22:45):
And also we find cinisthetes who have spatialization for the
Indian caste system, or shoe sizes, or temperatures, or historical
eras or primetime television line. So it can be anything
that's a sequence, and it just so happens that time
(23:05):
is sequential, but it's just a subset of the sequences
that you might learn in life. And that's why I
named this spatial sequence synesthesia in the literature, which is
the name now used in the field. It turns out
there are many, many forms of synesthesia, and one group
has estimated that there are one hundred and fifty two
(23:27):
different forms that have been reported. So anything you can imagine,
any kind of cross blending between the senses has been
reported at one point or another.
Speaker 2 (23:37):
Beyond the spatial sequence synesthesia.
Speaker 1 (23:40):
The next most common one seems to be the letters
or numbers mapping on to colors, or weekdays and months
to colors, or musical sounds to colors, or smells to colors,
or taste to colors. Most forms of synesthesia trigger color,
but we also find triggered tastes, smells, sounds, temperatures, emotions,
(24:02):
and so on. We find essentially any kind of cross
sensory blending that you can think of. It appears that
(24:25):
synesthesia is different for every synesthet Her associations are different
from hers, are different from hers. So the color that
gets triggered by the letter J or the number three
is a different color for everyone. Now why is this.
It could be that it's just about random wiring in
(24:46):
the brain, so the particular letter that matches up to
a particular color is arbitrary. But my colleagues and I
started to wonder if instead of randomness, it could be
about something that you imprinted on as a young child. Now,
this would give essentially the same results as randomness, because
(25:06):
you might, as a child see an alphabet quilt that
your mother made, and your mother's choices were just her
random choice, or an alphabet poster that your teacher made
at your preschool with some random choice, or some ad
in a magazine, and the idea is that those particular
letter color associations stuck for you. For most brains, the
(25:30):
statistics wash out, which means that one day you see
an A that's red, and the next day you might
see an A that's blue, and the next day yellow,
and so on, and so your brain learns that A
is not associated with any particular color, but in a
synesthetes brain, for whatever reason, perhaps the first association that
they see sticks and doesn't get washed out. Now, how
(25:55):
could you possibly test for this imprinting given that there's
no easy way to know what people saw in their childhoods?
And this is where science comes in. I collected detailed
colored alphabets from almost seven thousand cynisthetes who had these
colored alphabets, and with two colleagues at Stanford, we analyzed
(26:17):
those colors in detail, like person number one has a
red A and a purple B and a yellow C
and so on, and the next person has a brown
A and a crimson B and a gold C and
so on. So we analyzed this huge pool of cynisthetes
and we found something amazing. At least six percent of
(26:38):
the cynisthes had approximately the same colors. A through F
went red, orange, yellow, green, blue, purple, and then this
same sequence of colors was repeated G through L, and
then M through R and so on till the end
(26:59):
of the alphabet. This was so weird, and even more
of a clue is that we looked at people's birth
year and this sequence of colors never came up for
people who were born before the late nineteen sixties, and
then the proportion of people started to rise. So for
cyniesites born between nineteen seventy and nineteen eighty five, fifteen
(27:21):
percent of them had this same sequence of colors for
their letters, and then for those born after nineteen ninety
the proportion decreased again. So what was going on here?
We figured it out. In nineteen seventy one, a new
toy started finding its way into homes all over the
United States. It was the Fisher Price magnet set. This
(27:45):
was a set of refrigerator magnets that consisted of the
letters of the alphabet, and each one was colored and
it cycled through the letters red, orange, yellow, green.
Speaker 2 (27:56):
Blue, purple.
Speaker 1 (27:57):
So for those born in the decade after the magnets existed,
this color pattern reached fifteen percent. But for those who
grew up before the magnets existed, not a single one
of them had this pattern. So for all of these cyinsetes,
it was about whether they were exposed to these magnets
as children. Now, I want to be really clear that
(28:19):
the synesthesia wasn't caused by the Fisher price alphabet set
because the rest of the population saw it in the
seventies and eighties, but only three percent of people become cynisthetes.
It's simply that the sinisthetes who saw it imprinted on it,
so that.
Speaker 2 (28:36):
To them A always.
Speaker 1 (28:38):
Triggers red, and B orange, and C yellow and so on.
Synesthesia is something we think of as a different way
of perceiving the world. It's not a disorder or a disease,
because there's no disadvantage to it. In fact, in some cases,
cinisthetes tend to have better memories. So if I were
(29:00):
to tell you my phone number and you are a sinisthete,
you might forget some of the digits, but you may think, oh, yeah,
I remember it had a really nice autumn color pattern
to it, and so that would help you to reconstruct.
Speaker 2 (29:13):
It later when you're trying to think of it.
Speaker 1 (29:15):
You may have heard the termmneminists spelled with an m
N like Johnny mnemonic or a mnemonic device. Anyway, aneminist
is a person with an incredible memory. They can memorize
long lists of nonsense words, or really long strings of
numbers or series of locations. It turns out as far
(29:36):
as I can tell, that every single one of these
mneminists have synesthesia. They can take something like the digits
of Pie three point one four one five, nine, two
sixty five three five, and for thenemenist this may have colors,
such as the colors helped them to memorize the sequence.
And more than colors, they may have also textures and
(30:00):
personalities and genders and sizes, So as they're learning three
point one four one five, nine two sixty five, there's
a whole story landscape with a rich texture. So this
is how they memorize Pie to thousands of digits, while
for the rest of us who aren't synesthetic, for whom
(30:21):
all numbers are essentially alike, it's an almost impossible challenge.
I'll just mention that this advantage of synesthesia can also
become a confusion in some circumstances. So one synesthete has
particular colors that he sees for names like Mike and Dan,
but it turns out that he sometimes runs into trouble
(30:42):
at cocktail parties because it just so happens that Dave
and Rob have exactly the same colors for him as
Mike and Dan. So if your name is Dan, He's
pretty likely to mess up and call you Rob later
in the night. It turns out many artists have synesthesia.
Vasili Kandinsky was a music to color cinesthete. So if
(31:04):
you can picture a Kandinsky painting, you know that he
has these bold brushstrokes and vibrant colors. He makes these
abstracts with a sense of movement and energy. Boy, you
might not know is how he made them. He would
crank up his phonograph and he would stand in front
of his canvas and paint the images that came to
(31:26):
his head from the music that he was hearing. So
what you see on the canvas are his renditions of
his synesthetic experience. And many writers are cynisthetes. Vladimir Nabokov,
who wrote Lolita, was very synesthetic with letters and numbers.
These would trigger colors for him, and as a young
(31:49):
man he actually wrote quite a bit of poetry about
how he saw letters. When he was asked what color
his own initials were, the Bokhoff answered quote, the D
is a kind of pale, transparent pink. I think it's
called technically quartz pink. This is one of the closest
colors that I can connect with the V, and the N,
(32:11):
on the other hand, is a grayish yellowish oatmeal color. Interestingly,
different colors were triggered for him by the same letter
in different languages, so he said, quote the long A
of the English alphabet has for me the tint of
weathered wood, but a French A evokes polished ebony. This
(32:35):
black group also includes hard G, vulcanized rubber and R,
a sooty rag being ripped, oatmeal, N noodle, limp L,
and the ivory backed hand mirror of an O. Take
care of the whites. I am puzzled by my French on,
(32:56):
which I see as the brimming tension surface of alcohol
in a small glass. As a side note, Thebokoff loved butterflies,
and one of his favorites had yellow wings in a
black middle. So when yellow black yellow, and that corresponded
for him to the letters ab a so boom. That
became the title for his great novel Aida. It was
(33:19):
his little insider synesthetic joke, and many musicians are synesthetic.
Take Amy Beach, who was the first successful American female composer.
Her biographer noted that for her, C was white and
F sharp was black. And e was yellow and so on.
Until the end of her life she associated those colors
(33:41):
with those notes. Or The composer Olivier Mession, he was synesthetic,
and he described his purpose as quote, painting the visible
world in sound. He would describe things in his diary like, quote,
the gentle cascade of blue orange chords. This is the
way that he would describe particular sequences of music. There
(34:05):
are lots of musicians with synesthesia. Billy Joel, Duke, Ellington, Torry,
Amos Grimes. The singer Billy Eilish recently told Rolling Stone quote,
every person that I know has their own color and
shape and number in my head, but it's normal to me.
She says that her brother Phineas is an orange triangle,
(34:28):
although his name Phineas is dark green. Pharrell Williams also
has synesthesia. For him, each note has a color, and
his musical group Nerd named one of their albums Seeing Sounds.
(34:59):
Now people have speculated, because of this sort of thing,
that maybe there's an overrepresentation of sinnisthetes in the artistic community.
But I just want to point out that we don't
actually know if that's true, because no one's ever gone
in and tested the community of accountants or deep sea divers.
All we know is that we can point to a
(35:20):
lot of artists who are synesthetic, and so we can
hypothesize that maybe synesthesia provides some pull to those professions.
In other words, if you have this slightly richer sort
of perception, then maybe you gravitate towards certain sorts of pursuits.
By the way, I should note that not every artist
(35:40):
who does something synesthetic is actually a synisthet The composer
Scriabin was really interested in the effects of putting sound
and color together, and he thought that would provide a
really strong resonance for the listener. So he invented a
color organ. When you hit the notes, you're not only
(36:00):
playing the musical sound, but there are spotlights of different
colors coming out of the top. But Screopin wasn't actually
a synisthete himself he was just exploring cool things and
was influenced by the fashions of the art world at
that moment. So not everyone who does this sort of
thing is actually a synesthee. And this leads me to
(36:21):
a really important point. How can you tell if someone
really is synesthetic? How can you test for this. So
when someone tells you that they're a synisthete, how could
you ever know if they're just being artistic or metaphorical
or poetic, or lying or just trying to get attention.
(36:42):
So my colleagues and I, over the past fifteen years,
have developed a whole series of tests where we can
show when synesthesia is actually a real perceptual experience. And
I want to tell you how we do that. It
has everything to do with the consistency of people's perceptions.
So if you're a cynisthete who sees eight as lavender,
(37:06):
you're always going to see it as lavender. But if
I were to ask you to make up some colors
right now, and then I ask you again a year
from now, if you're not synesthetic, you're not going to
be able to get these same color associations. But if
you are synesthetic, it'll be the same colors. So many
years ago I launched a website called cinnisthete dot org,
(37:30):
and it's a battery of tests that are freely available.
So if you think you might be a synthete, go
to the site and take the tests. What we can
do this way is rigorously determine who exactly is synesthetic
and who's not. Here's the method. It has anything to
do with internal consistency. So we show you a letter
(37:51):
of the alphabet at random, say a J, and you
see a color palette on the screen, and by moving
a slider around, you can get to any hue, any color,
and by moving a second slider around, you can specify
whatever saturation, in other words, how dark or bright it is.
(38:11):
So you pull the sliders around and you pick the
color that best matches your synesthetic perception for that letter.
And this is out of sixteen million different colors that
can be displayed on a computer screen. And when you
found the best one, you click submit, and then you
get the next random letter or number, say the letter
(38:32):
W or the number three or whatever, and you find
exactly that color that best matches for that one. And
the trick is we present you with each letter and
each number three times, each in random order. So the
idea is that if you are really a synesthee, you're
(38:53):
going to land on the same shade of color for
let's say the letter J every time. And if you're
a sinisthete, it turns out it's very hard to fake that.
So when you look at the results for cynisthetes and
for control subjects who are asked to fake synesthesia, we
can measure the amount of difference in the colors that
(39:14):
they chose. And what we see is that for a
real cinisthete, it's easy. Every time she's presented with the
letter T, she picks the same color or E, it's
the same color every time, and so on. Whereas for
somebody who's asked to use free association or memory or
whatever but they're not actually synesthetic, it's really difficult to
(39:34):
get the same colors. It's a very hard test to
pass to remember what you said fifty seven trials ago
and find that color again out of sixteen million possible colors.
So this turns out to be a powerful way that
we can distinguish who is a cynisthete and who is not.
And we actually have several levels of testing to make
(39:56):
it absolutely impossible to cheat. So, for example, after we've
collected your colors, we then flash it to you on
the screen. So let's say it's the letter H. We
flash an H that's either the color that you've had
chosen or a different color from somewhere else in your palette,
and you have to say as quickly as you can
whether it matches or didn't match your perception. And for
(40:20):
a real cynisthete, if I'm flashing the orange h they'll say, yeah,
that match, and if I flash a green age, they'll
say that doesn't match. But for someone who's just faked
their way through, it's something they're terrible at, both in
terms of accuracy and reaction time. So this is how
we can make sure that we find real cynisthetes. And
(40:43):
we've translated this battery into many different languages, including Chinese
and Hebrew as well as a whole bunch of European languages,
and this way we can find out what's going on
not only in French and Spanish and German, but also
in different alphabetic systems like Cyrillic or Hebrew or Chinese.
Also we can test all sorts of different forms of synesthesia.
(41:05):
And what we have now are about eighteen different forms
of tests, like musical notes to color, or instrument tambers
to color and so on. And it turns out with
this sort of testing we can finally get the sample
sizes that we need, because it turns out that all
the previous literature had a sample size of one. Up
(41:26):
until the early two thousands, it was all single case
studies where people said, hey, I met a cinisthet and
I asked her these questions and here are her answers.
And then people started publishing papers with a participant group
size of two or four, and a few papers had
eight people in them. What we've done now is changed
the game on that because we have rigorously verified over
(41:48):
sixty four thousand cinisthetes and we have their data in
exquisite detail, and this allows us to alter the scientific
playing field. Now, there were a few papers on synesthesia
in the eighteen hundreds, but then synesthesia essentially slipped out
of the scientific spotlight for most of the twentieth century,
(42:09):
and that was because psychology was dominated by the behaviorist
school of thought, where the idea was that we're just
input output reflex machines and it wasn't really appropriate or
scientific to talk about private subjective experience. So as a result,
synesthesia fell to the wayside. But fundamentally, if there's one
(42:32):
thing we know, it's that it feels like something to
have a brain. We have private subjective experience consciousness, and
so as this question has become a serious one in
our field. Synesthesia has risen from the ashes as a
powerful inroad to understanding consciousness. So what causes synesthesia? My
(42:55):
colleagues and I have performed brain imaging and what we
found is that in a cynisthete, neighboring areas of the
brain have a little bit more cross.
Speaker 2 (43:06):
Talk than normal.
Speaker 1 (43:07):
So regions of the brain that care about letters and
numbers happen to be close to other regions that care
about colors, and in a sinisthete, there's a bit more
cross talk between these areas than in a typical brain.
So think of it like two neighboring countries with porous borders.
And some years ago my lab started a long term
(43:29):
project to find the gene or genes that underlie synesthesia.
And to my mind, this is the first step in
a new subfield, which I'm calling perceptual genomics, which just
means understanding the subtle genetic differences that make you see
the world differently than I do. As a scientific community,
(43:51):
we're always looking for the genes for predisposition to diabetes
or aortic stenosis or Parkinson's, or that make some people
taller or broader or red haired or whatever. The same
techniques can be used to find the genes that make
our realities a little different from one another. Something that
(44:12):
struck me, as I mentioned earlier, is that there are
many different subtypes of synesthesia. Now are these all the
same thing or different? In other words, are all synesthesias
due to a single genetic change or are there totally
separate mechanisms involved? So how could I answer this? We
tested all these thousands of people on synesthesia, and we
(44:35):
asked from the data how the different types cluster with
one another. In other words, if you have colored letters,
what is the likelihood that you also have instrument tamber
synesthesia or colored months or colored musical notes or something
like that. How do these different things clump with each other.
(44:56):
What we found is that if you have colored letters
in number, you're really likely to have colored weekdays or months,
but you're not terribly likely to have other forms of
synesthesia like vision to sound or taste to touch. And
what we found is that the different types fall into
five different clusters.
Speaker 2 (45:17):
If you have touch to color.
Speaker 1 (45:20):
You're not really likely to have sound to touch or
other types. They fall into these different groups. And if
you want to know more about this, go to Eagleman
dot com slash podcast to see our different papers on this. Now,
this is an important finding that I'm mentioning because it
suggests that synesthesia is not a single thing genetically, but
(45:41):
there may be at least five different things that we're
all putting under the same umbrella. And the reason we
put them under the same umbrella is simply because they
have something in common. There's a mixture of the senses,
but they might actually be underpinned by different genetic bases.
And this is something I'll talk about in future episodes,
(46:02):
because we're generally seeing the same thing when we look
at other things like schizophrenia. People can present clinically very differently,
but we lump it all under schizophrenia. But I think
it's likely that in ten years from now, we'll talk
about multiple types of schizophrenia, and eventually we'll have totally
new names that identify the different genetic causes that happen
(46:27):
to give rise to these similar conditions that we stick
under the same umbrella. So the one that I've been
concentrating on is the one I call colored sequence synesthesia,
because as I mentioned, the thing to note is that
letters and numbers and weekdays and months are all overlearned sequences.
(46:48):
They're all arbitrary sequences that you memorize when you're about
four or five years old. And the way I started
this genetic study was by crashing a wedding and asking
everyone to spit into spitkits. Now why a wedding, It's
because the whole family tree of this family with synesthesia
was there, so I could march through the tree to
(47:10):
see who has synesthesia and who doesn't, and then do
what's called a family linkage analysis, which looks at how
the small genetic changes march through the family tree and
you find out which tiny changes are tracking with who
has synesthesia. Now, we're still working on this with lots
of different families in their trees, and it may well
(47:32):
be that there are different genetic changes in different families,
but we're getting closer to identifying at least some of
the genes involved. Now, this might involve an increased wiring
in a cineste's brain, or it might involve a slight
imbalance of the inhibition and excitation in the brain such
(47:52):
that you have activity in one area that kindles activity
in the neighboring area. I actually favor the second hypoth
this because non synesthetes can experience synesthesia with drugs, and
people can also experience synesthesia sometimes if they're super tired
and someone slams the door, they'll see colors. Even for synesthetes,
(48:15):
there synesthesia waxes and wanes a bit. Whether they're stressed
or fatigued, or on cigarettes or alcohol, or antidepressants or
anti epileptics. All these things change the quality of their synesthesia.
And that has the feeling of something to do with
the chemical balance, not simply the hardwiring. So I think
(48:36):
that when we find the gene or genes, will be
able to show that it's something associated with the balance
between inhibition and excitation in the brain. So what's amazing
about synesthesia is that what might be a single nucleotide
change in your genome changes the way that you see
the world. It changes the way that you experience and
(49:00):
it's your reality. So this will be the first time
that we're able to say, if you change this little
A or C or T or G over here, now
you are seeing the world differently. Now I want to
ask you a question. I'm going to play two notes
on my piano, which one is brighter, which one is bigger.
(49:26):
I've asked this informally to thousands of nonsynesthes and essentially
everybody answers that the high note is brighter and the
low note is larger. And that's strange, right, because all
I'm doing is playing some notes, and you're mapping that
sound onto brightness and onto size. So what this suggests
(49:48):
is that everyone has some cross connectivity in the brain.
And when you look at the micro anatomy, what you
find is that there are fibers in the brain carrying
visual information that go into the auditory part of your brain,
and there's fibers carrying auditory information that plug straight into
the visual parts of your brain. So this isn't everybody's brain.
(50:11):
It turns out there's naturally a lot of mixing of
the senses, and that's presumably why we all understand expressions
in the language that cross the senses, like oh, that's
a loud tie, or that's cool jazz, or she has
a sweet personality, or that's sharp cheese. Cross sensory expressions
(50:37):
are all over the language, and they kind of work
with everybody.
Speaker 2 (50:41):
We all know what it means when.
Speaker 1 (50:43):
You talk about these So this is the sense in
which we all share something like synesthesia, but we only
call it synesthesia when it's a cross sensory connection. That's rare,
And in this way synesthesia can serve as a terrific
inroad into understanding consciousness, both what people have in common
(51:04):
and what they experience differently. It illustrates a theme that
I'm going to come back to a lot in this podcast,
which is that people can be quite different on the inside. So,
to wrap up today's episode, reality is not one size
fits all. Two people can stand right next to each
other watching the Northern lights, and for one a sound
(51:26):
is internally triggered by the visuals, and not for the other.
Two humans watching the same event and having divergent experiences.
And the important lesson here is that if we're just
trying to understand our own reality, we're like fish in
water trying to describe water. It's impossible to describe what
(51:47):
water is because we've never seen anything other than that.
But when you see a different way that things can be,
that gives you a broader platform from which to build theories,
and that allows us to make progress on one of
our deepest goals in neuroscience to understand how the microscopic
(52:08):
activity in these three pounds of wet, gushy alien computational
material maps onto the world that you see and enjoy
every day, How it maps onto the view that you're
looking at right now, or the feel of your clothes
on your skin, or the sound of my voice in
your ear. That's all for this week. To find out
(52:34):
more and to share your thoughts, head over to eagleman
dot com slash podcasts. If you think you might have
synesthesia and you want to take the tests, go to
sinnisthet dot org. Until next time, I'm David Eagleman, and
this is Inner Cosmos.
Why do some people think that the Northern lights make
noise and other people say that that's impossible. And why
did Pythagoras think that numbers had colors and personality? And
what does any of that have to do with creators
like Vladimir Nabokoff and Billie Eilish, And why do you
think that a high note on the piano is brighter
(00:29):
than a low note. Welcome to Inner Cosmos with me,
David Eagleman. I'm a neuroscientist and an author at Stanford University,
and I've spent my whole career studying the intersection between
how the brain works and how we experience life. On
(00:55):
today's episode, we're going to talk about how we can
all experience reality a little bit differently. Okay, so this
story begins in the early nineteen thirties. You've heard about
the Northern lights, or maybe you've even seen them in person.
They're these rippling rivers of green blue light in the sky.
(01:15):
But here's the really strange part. About one hundred years
ago some people started to make the claim that the
northern lights make noise. In nineteen thirty one, in the
journal Nature, a scientist named Harold's Fairdrop wrote a short
paper that he called Audibility of the Aurora polaris, and
(01:35):
he wrote, quote, it cannot be doubted that many persons
have heard a distinct sound when watching a brilliant display
of aurora. Communications regarding the auroral sound appear now and then,
and recently.
Speaker 2 (01:52):
Mister J. H.
Speaker 1 (01:53):
Johnson has collected a great number of reports on the
auroral sound in his pamphlet concern the Aurora borealis. Then,
in nineteen thirty three in the journal Science, someone named
Clark Garber wrote another letter on the audibility of the
Aurora borealis, and Garber wrote quote, some scientists have claimed
(02:15):
with much positiveness that the aurora emits no audible sounds.
In my own mind, there can be no doubt left
as to the audibility of certain types of aurora, for
I have heard them under conditions when no other sound
could have been interpreted as such, for no other sounds
were present. And he goes on to say that he
(02:37):
first heard about the possibility that the aurora makes sounds
from the eskimos, and he says he was skeptical at first,
but then he experienced this sound himself. Now I stumbled
on these papers a few years ago, and I was
surprised because the problem is that it's not scientifically possible
for the Aurora to make sound. The Northern Lights happen
(03:01):
because photons from the Sun are banging into gases in
the Earth's upper atmosphere, and that causes all that amazing light.
But those collisions are happening eighty kilometers up in the sky,
which means that even if there were sound, it would
take about four minutes for that sound to get down here.
And yet people who claim to hear the sound say
(03:24):
they see it happening in lockstep with the lights. And
more importantly, for sound to travel it needs a medium
like air, and that's because sound moves as compression of
the air. In other words, molecules in the air get
pushed closer together and farther apart, and that's what a
sound wave is. But at the altitude where the Northern
(03:45):
Lights come into being, the atmosphere is essentially a vacuum.
Speaker 2 (03:50):
So this means there's probably no.
Speaker 1 (03:52):
Sound happening even up there, and if there were, it
couldn't get all.
Speaker 2 (03:56):
The way to us until four minutes later.
Speaker 1 (03:58):
So this became a top of debate because as time
went on, thousands of Arctic explorers listened carefully for these
sounds but didn't hear anything. So this idea of the
northern lights making noise came to be understood as a superstition.
So what was happening here? Were some people simply lying
(04:20):
in scientific journals It's happened before, But it seems that
some people really believed and still believe, the lights make sound,
even though the physics don't seem to allow that. So
worse Ferdrup and Garber lying, were they looking for attention
that they somehow have better hearing? Even today? This is
(04:41):
contentious in geophysics. Some people argue from their personal experience
that it happens, and others point out that it simply can't.
To unpack this mystery, let's jump back even farther back
another twenty five hundred years to Pythagoras. Pythagoras was one
(05:01):
of Greece's most famous philosophers, and he massively influenced the
trajectory of Western thought through his religious teachings his political teachings.
In part this was due to his influence on Plato
and Aristotle. But you've probably heard of Pythagoras because of
his love of numbers. He loved geometry and theories about
(05:24):
instrument tuning and the theory of proportions, and you'll probably
remember the Pythagorean theorem from school in a right triangle,
A squared plus B squared equals C squared. But there
was something very odd about Pythagoras's relationship with numbers. I'm
going to quote from the Yale historian Robert Brumbaugh, who
(05:47):
notes that for Pythagoras quote, each number had its own personality,
masculine or feminine, perfect or incomplete, beautiful or ugly. For Pythagoras,
ten was the very best number. This feeling modern mathematics
has deliberately eliminated, but we still find overtones of it
(06:11):
in fiction and poetry. Now, how could numbers have gender
and personality? Did Pythagoras have fundamental insight about numbers that
the rest of us couldn't see? Or was he making
up stuff to impress his followers, or was he mentally
(06:32):
ill or taking drugs. The way that he personified numbers
is traditionally discussed as an interesting oddity, or occasionally you'll
find numerologists who cite Pythagoras's view as evidence that he
had a cosmic insight into the true natures of numbers.
I've seen websites that springboard from Pythagoras's number personalities to
(06:56):
sell new age models of the nature of the universe.
But most people don't believe that the number five has
a gender or a personality. So what was going on
here and what does this have to do with the
scientists who claim to hear sounds from the Northern Lights.
The answer to both these mysteries is related to something
(07:16):
I'm going to discuss a lot across many episodes of
this podcast, and that is the difference in people's internal worlds.
We all like to believe that our experience of the
world is the same as everyone else's. But the key
to unlocking the mystery of the Northern Lights or Pythagoras's
view of numbers is to understand that people can have
(07:39):
very different realities on the inside. The interesting part, as
we'll see, is that we accept the reality presented to us.
Your brain constructs a story about what's going on out there,
and you accept that as your reality. So imagine I
showed you a picture of a crowd of people. If
(08:00):
you're color blind, all you see are shades of gray.
If you're not colorblind, you see it in full color.
But either way, that's the reality that you know. And
we now know that a very tiny fraction of the
female population doesn't just have three types of color photoreceptors
in their eyes, but they have four types because of
(08:22):
a mutation, and as a result, they perceive colors that
the rest of us can't even imagine. Their reality is different.
So the key is we accept whatever reality our brains
serve up to us. Okay, So this all leads to
a very old philosophical question which I think everyone has
(08:44):
asked at some point in their lives. How do you
know that what I see as blue is what you
see as blue? My parents taught me to call that
thing blue, and your parents taught you to call it blue.
Speaker 2 (08:59):
Two. But inside your.
Speaker 1 (09:01):
Head and inside my head, it might be a different experience.
Speaker 2 (09:05):
Right.
Speaker 1 (09:06):
I might be seeing it as what you would think
of as green, But it doesn't matter, and we'd never
know as long as we can transact in the outside world.
In other words, if I say, hey, can you pass
me that blue thing, and we both call it blue,
then the word suffices, even if we're having a different
(09:26):
internal experience and it turns out. The situation might be
even worse than that. It may be that what I
call vision and what you call vision are totally different.
I might see the world completely upside down from the
way that you see the world, and it wouldn't matter
as long as we can agree on things out there,
and I can throw a ball and you can catch it.
(09:48):
So what my colleagues and I have worked on for
years is taking this question or we having different lives
on the inside and elevating that from the realm of
phys sophical speculation to actual scientific experiment. And one way
to get at that this was something my lab is
studied for fifteen years called sinnesthesia. Synesthesia is a condition
(10:14):
in which one person might be seeing reality a little
bit differently from another. So you know the word anesthesia,
that means no feeling. Synesthesia means joined feeling. It's a
blending of the senses. Now, there are many forms of synesthesia,
and one of the most common is where a person
(10:36):
looks at numbers or letters and that triggers an internal
experience of color. So for a given synesthete, her eight
might trigger the experience of blue. She still sees the
number eight on the page. There if I were to
write eight with black ink on a white page, she'd
say that she can see the number, but seeing the
(10:57):
number eight triggers a blue experience, an internal experience of blue.
And it's just self evidently true for her that eight
and blue are connected. Now this isn't just a memorized
thing that she says, but it's an actual experience. And
for her, maybe five is yellow, and Saturday is orange,
(11:20):
and November is purple and so on. Now, the first
thing to note is that sequences that we learn, like
letters and numbers and weekdays and months, these are drilled
into the brain really deeply. They're known in the field
as overlearned sequences, and these are the things that trigger synesthesia.
(11:42):
And interestingly, this often goes beyond color in when flavor
of synesthesia, sequences come to have gender and personality and
other qualities. So one cynesthete describes the number three as
a vain, elitist girl, while seven is a shy, wimpy boy.
(12:05):
This same cynisthe described by my colleague Sean Day. She
also noted that she doesn't like certain number combinations, like
ninety four.
Speaker 2 (12:14):
That quote result.
Speaker 1 (12:16):
In putting four, which is a plain but decent, hardworking
older woman and nine together as they greatly dislike each
other and do not get along well. And this is
what was going on with Pythagoras. He had this not
uncommon form of synesthesia, but his followers didn't know this,
(12:36):
so they presumably thought he was tapped into some cosmic
truth about numbers. He obviously liked numbers, but that doesn't
mean he had access to some deeper significance that others didn't.
How do we know that, Because each person with this
particular type of synesthesia has a different association between a
(12:57):
particular number and a gender personality. So you might think
three is male and kind, and someone else might think
three is female and a bit of a comic, and
so on. There is no right answer. So we're gonna
come back to this in a moment, But first I
want to tell you about some other forms of synesthesia.
(13:18):
It's not just colors or genders or personalities triggered by
overlearned sequences. There's also a flavor of synesthesia in which
what you hear causes a visual experience. So you might
listen to music and that causes you to see moving
shapes or colors. In my book, Wednesday's Indigo Blue. I
(13:41):
have a picture of a shape that looks like a
colorful caterpillar, and this is what one synesthete sees. She
actually sees this when her furnace kicks on and goes whoosh.
She has this visual experience that flashes for her. Her
visual system gets tickled by the noise, and senses can
be triggered in the other direction, where something visual leads
(14:05):
to a sound. For some people, when they watch movement
like a swarm of moving birds or an electric sign blinking,
they feel like they hear a sound with it. They
don't see the motion by itself. Their brain imposes sound
on top of that. It's impossible to separate the motion
and the sound. And I've proposed that this is the
(14:27):
solution to the mystery of the Northern lights. It's impossible
from a physics point of view for the lights to
be making synchronized noise. But what is possible is for
a small fraction of the population to be cinnesthetic, such
that when they see the beautiful moving lights, they hear sound.
(14:48):
And because of their assumption that our senses tell us
the truth and that everyone should be having the same experience,
this has led to over a century of debate about
whether the lights make noise or not, because if your
sphare drop or Gerber or any of the others who
hear the sounds, you'll sit down and you'll write a
letter to nature or science and insist that you can
(15:11):
hear it. The important lesson is that we all assume
our senses tell us the truth and that everyone is
tapped into the same reality. But when we realize that's
not necessarily the case, we can take a higher view
on the scientific literature and look at all these papers
(15:31):
going back and forth about whether the northern lights make noise,
and we can understand the game at a different level.
For most people the answer is no, they don't make noise,
and for some it's yes. Beyond the relationship of sound
and vision, there are dozens of forms of synesthesia. My
(15:51):
colleagues and I have found that essentially any sense that
you can imagine can be mixed with another. One form
of synesthesia involves tastes shapes, So when people taste something,
it makes them feel like they're touching something with their fingertips.
So you might take a sip of soup and you
feel something cold and pointy on your fingertips. Or one
(16:13):
guy determines whether his chicken is cooked right this way.
He tastes it and judges by what he's feeling on
his fingertips, is it smooth or glassy or spiky. He
comes to be a good cook that way. And there's
also musical synesthesia. For a lot of people, different notes
of the scale will trigger a color experience. For one
(16:36):
cynisthee that I test in the lab, when she hits
the note A on the piano, that's pink, the note
B is blue. C is goldish white like sunlight. B
is silvery white like moonlight. E is fiery orange, and
(16:58):
so on, So she experiences very specific colors that get
triggered when she hears specific notes. And I know a
professional drum tuner who goes around for all the famous
rock and roll bands and tunes their drums, and he
does it with color, so he can tell if the
drum is a little bit sharp or a little bit
(17:18):
flat by the color that he sees in response to
the sound. Now, not all people with music synesthesia have
their percepts triggered by a pitch a note. For some people,
it's the interval between notes like a chord that matters.
So for one woman, different chords trigger different, very particular
(17:41):
tastes in the mouth. In a paper in the journal Nature,
she reported that she uses these sinnesthetic associations to identify
which chord was just played. And synesthesia can also be
triggered by an instrument's tamber, the way that it sounds.
So when a person hears the music of a violin
versus a tuba, versus a cello versus a flute, the
(18:06):
timbre of the instrument can trigger very different experiences in
terms of colors or visualized shapes or whatever. So two
people might listen to a clarinet playing and that triggers
different internal experiences. One of them sees it as a flat,
horizontal shape with spring like protrusions sticking out, and the
(18:28):
other person sees it as a thick ribbon that's oscillating,
and so on. For different cinisthetes. And beyond shapes or colors,
it can trigger other notions as well, like personalities. One
cinis The reports that the obo is quote profoundly emotional
and thoughtful, with drawn, introspective, and prone to melancholy, while
(18:54):
she describes the flute as quote feminine, sweet, innocent, naive
the personalities of the different instruments. They're not generic, they're
rich and detailed. The triggered perception can also be a
physical sensation, like a physical state of your body. For
one Cyniceitt that I interviewed, different chords make her feel
(19:17):
like her body is in different positions physically, So when
she feels one chord, she feels like she's standing upright
with her feet on the ground, or stepping onto a
stare or soaring in the sky. She happens to be
a professional musician, so when she's memorizing a piece of music,
(19:41):
it's like memorizing a series of dance moves. And there's
one more form, which is likely the most common, around
ten percent of the population experience it. It's when people
perceive sequences like the days of the week or the
months of the year, as though they have a specific
space location in relation to their body, like March is
(20:04):
off here to the left, and April is next to it,
and May is a little bit higher and off next
to that. For every month or a weekday or numbered
things like that, they have a specific spatial location that
the person can identify where it seems to them that
the thing exists. It's just self evidently true to them
(20:25):
that that member of the sequence has that particular spatial location.
This form of synesthesia is not a hallucination. It's not
that you actually see April right there visually.
Speaker 2 (20:37):
It's that it's just obviously true to you.
Speaker 1 (20:40):
That April would occupy that spatial location to you. It
would be like if I asked you to imagine an
apple five feet in front of you. So you're picturing
the apple there and it's got a particular spatial location
with respect to your body, and you can imagine it,
but you're not actually hallucinating it. But if I ask
(21:00):
you where that apple is, that's the spatial location that
it has. A lot of people have this form of
synesthesia for years, like the year nineteen seventy nine has
a specific spot in space and relation to your body,
as does twenty twenty one or twenty fifty seven and
everything in between, and the years sit on this spatial timeline.
(21:22):
The timeline isn't necessarily straight. It can curve or take
sharp turns, and it typically moves with the passing of
each year. Now, what's interesting is that for many cinisthetes,
a year in the past moves behind them, say the
year twenty twenty one. Why because that year has already happened,
so it moves behind you, while a year like twenty
(21:45):
forty two is often the distance ahead of you. But
for other cynisthetes, it's exactly flipped. A year in the
past is in front of them because they already know
what happened in twenty twenty one, but year like twenty
forty two hasn't happened yet, so they don't know anything
about it. It's as invisible to them as an object
(22:07):
that is behind them. I'll just note that another research
group called this form of synesthesia time space synesthesia because
they looked at things like weekdays and months and years
and said, hey, those all have something to do with time.
But I want to emphasize that this is not the
correct way to understand this, because this same spatialization happens
(22:29):
with number lines like one, two, three is over here,
that it takes a right turn here for four through seven,
then eight, nine, ten climb straight up, then eleven through
twenty shoot off in a straight line, and then twenty
one through thirty are stacked above that like that.
Speaker 2 (22:43):
Kind of thing.
Speaker 1 (22:45):
And also we find cinisthetes who have spatialization for the
Indian caste system, or shoe sizes, or temperatures, or historical
eras or primetime television line. So it can be anything
that's a sequence, and it just so happens that time
(23:05):
is sequential, but it's just a subset of the sequences
that you might learn in life. And that's why I
named this spatial sequence synesthesia in the literature, which is
the name now used in the field. It turns out
there are many, many forms of synesthesia, and one group
has estimated that there are one hundred and fifty two
(23:27):
different forms that have been reported. So anything you can imagine,
any kind of cross blending between the senses has been
reported at one point or another.
Speaker 2 (23:37):
Beyond the spatial sequence synesthesia.
Speaker 1 (23:40):
The next most common one seems to be the letters
or numbers mapping on to colors, or weekdays and months
to colors, or musical sounds to colors, or smells to colors,
or taste to colors. Most forms of synesthesia trigger color,
but we also find triggered tastes, smells, sounds, temperatures, emotions,
(24:02):
and so on. We find essentially any kind of cross
sensory blending that you can think of. It appears that
(24:25):
synesthesia is different for every synesthet Her associations are different
from hers, are different from hers. So the color that
gets triggered by the letter J or the number three
is a different color for everyone. Now why is this.
It could be that it's just about random wiring in
(24:46):
the brain, so the particular letter that matches up to
a particular color is arbitrary. But my colleagues and I
started to wonder if instead of randomness, it could be
about something that you imprinted on as a young child. Now,
this would give essentially the same results as randomness, because
(25:06):
you might, as a child see an alphabet quilt that
your mother made, and your mother's choices were just her
random choice, or an alphabet poster that your teacher made
at your preschool with some random choice, or some ad
in a magazine, and the idea is that those particular
letter color associations stuck for you. For most brains, the
(25:30):
statistics wash out, which means that one day you see
an A that's red, and the next day you might
see an A that's blue, and the next day yellow,
and so on, and so your brain learns that A
is not associated with any particular color, but in a
synesthetes brain, for whatever reason, perhaps the first association that
they see sticks and doesn't get washed out. Now, how
(25:55):
could you possibly test for this imprinting given that there's
no easy way to know what people saw in their childhoods?
And this is where science comes in. I collected detailed
colored alphabets from almost seven thousand cynisthetes who had these
colored alphabets, and with two colleagues at Stanford, we analyzed
(26:17):
those colors in detail, like person number one has a
red A and a purple B and a yellow C
and so on, and the next person has a brown
A and a crimson B and a gold C and
so on. So we analyzed this huge pool of cynisthetes
and we found something amazing. At least six percent of
(26:38):
the cynisthes had approximately the same colors. A through F
went red, orange, yellow, green, blue, purple, and then this
same sequence of colors was repeated G through L, and
then M through R and so on till the end
(26:59):
of the alphabet. This was so weird, and even more
of a clue is that we looked at people's birth
year and this sequence of colors never came up for
people who were born before the late nineteen sixties, and
then the proportion of people started to rise. So for
cyniesites born between nineteen seventy and nineteen eighty five, fifteen
(27:21):
percent of them had this same sequence of colors for
their letters, and then for those born after nineteen ninety
the proportion decreased again. So what was going on here?
We figured it out. In nineteen seventy one, a new
toy started finding its way into homes all over the
United States. It was the Fisher Price magnet set. This
(27:45):
was a set of refrigerator magnets that consisted of the
letters of the alphabet, and each one was colored and
it cycled through the letters red, orange, yellow, green.
Speaker 2 (27:56):
Blue, purple.
Speaker 1 (27:57):
So for those born in the decade after the magnets existed,
this color pattern reached fifteen percent. But for those who
grew up before the magnets existed, not a single one
of them had this pattern. So for all of these cyinsetes,
it was about whether they were exposed to these magnets
as children. Now, I want to be really clear that
(28:19):
the synesthesia wasn't caused by the Fisher price alphabet set
because the rest of the population saw it in the
seventies and eighties, but only three percent of people become cynisthetes.
It's simply that the sinisthetes who saw it imprinted on it,
so that.
Speaker 2 (28:36):
To them A always.
Speaker 1 (28:38):
Triggers red, and B orange, and C yellow and so on.
Synesthesia is something we think of as a different way
of perceiving the world. It's not a disorder or a disease,
because there's no disadvantage to it. In fact, in some cases,
cinisthetes tend to have better memories. So if I were
(29:00):
to tell you my phone number and you are a sinisthete,
you might forget some of the digits, but you may think, oh, yeah,
I remember it had a really nice autumn color pattern
to it, and so that would help you to reconstruct.
Speaker 2 (29:13):
It later when you're trying to think of it.
Speaker 1 (29:15):
You may have heard the termmneminists spelled with an m
N like Johnny mnemonic or a mnemonic device. Anyway, aneminist
is a person with an incredible memory. They can memorize
long lists of nonsense words, or really long strings of
numbers or series of locations. It turns out as far
(29:36):
as I can tell, that every single one of these
mneminists have synesthesia. They can take something like the digits
of Pie three point one four one five, nine, two
sixty five three five, and for thenemenist this may have colors,
such as the colors helped them to memorize the sequence.
And more than colors, they may have also textures and
(30:00):
personalities and genders and sizes, So as they're learning three
point one four one five, nine two sixty five, there's
a whole story landscape with a rich texture. So this
is how they memorize Pie to thousands of digits, while
for the rest of us who aren't synesthetic, for whom
(30:21):
all numbers are essentially alike, it's an almost impossible challenge.
I'll just mention that this advantage of synesthesia can also
become a confusion in some circumstances. So one synesthete has
particular colors that he sees for names like Mike and Dan,
but it turns out that he sometimes runs into trouble
(30:42):
at cocktail parties because it just so happens that Dave
and Rob have exactly the same colors for him as
Mike and Dan. So if your name is Dan, He's
pretty likely to mess up and call you Rob later
in the night. It turns out many artists have synesthesia.
Vasili Kandinsky was a music to color cinesthete. So if
(31:04):
you can picture a Kandinsky painting, you know that he
has these bold brushstrokes and vibrant colors. He makes these
abstracts with a sense of movement and energy. Boy, you
might not know is how he made them. He would
crank up his phonograph and he would stand in front
of his canvas and paint the images that came to
(31:26):
his head from the music that he was hearing. So
what you see on the canvas are his renditions of
his synesthetic experience. And many writers are cynisthetes. Vladimir Nabokov,
who wrote Lolita, was very synesthetic with letters and numbers.
These would trigger colors for him, and as a young
(31:49):
man he actually wrote quite a bit of poetry about
how he saw letters. When he was asked what color
his own initials were, the Bokhoff answered quote, the D
is a kind of pale, transparent pink. I think it's
called technically quartz pink. This is one of the closest
colors that I can connect with the V, and the N,
(32:11):
on the other hand, is a grayish yellowish oatmeal color. Interestingly,
different colors were triggered for him by the same letter
in different languages, so he said, quote the long A
of the English alphabet has for me the tint of
weathered wood, but a French A evokes polished ebony. This
(32:35):
black group also includes hard G, vulcanized rubber and R,
a sooty rag being ripped, oatmeal, N noodle, limp L,
and the ivory backed hand mirror of an O. Take
care of the whites. I am puzzled by my French on,
(32:56):
which I see as the brimming tension surface of alcohol
in a small glass. As a side note, Thebokoff loved butterflies,
and one of his favorites had yellow wings in a
black middle. So when yellow black yellow, and that corresponded
for him to the letters ab a so boom. That
became the title for his great novel Aida. It was
(33:19):
his little insider synesthetic joke, and many musicians are synesthetic.
Take Amy Beach, who was the first successful American female composer.
Her biographer noted that for her, C was white and
F sharp was black. And e was yellow and so on.
Until the end of her life she associated those colors
(33:41):
with those notes. Or The composer Olivier Mession, he was synesthetic,
and he described his purpose as quote, painting the visible
world in sound. He would describe things in his diary like, quote,
the gentle cascade of blue orange chords. This is the
way that he would describe particular sequences of music. There
(34:05):
are lots of musicians with synesthesia. Billy Joel, Duke, Ellington, Torry,
Amos Grimes. The singer Billy Eilish recently told Rolling Stone quote,
every person that I know has their own color and
shape and number in my head, but it's normal to me.
She says that her brother Phineas is an orange triangle,
(34:28):
although his name Phineas is dark green. Pharrell Williams also
has synesthesia. For him, each note has a color, and
his musical group Nerd named one of their albums Seeing Sounds.
(34:59):
Now people have speculated, because of this sort of thing,
that maybe there's an overrepresentation of sinnisthetes in the artistic community.
But I just want to point out that we don't
actually know if that's true, because no one's ever gone
in and tested the community of accountants or deep sea divers.
All we know is that we can point to a
(35:20):
lot of artists who are synesthetic, and so we can
hypothesize that maybe synesthesia provides some pull to those professions.
In other words, if you have this slightly richer sort
of perception, then maybe you gravitate towards certain sorts of pursuits.
By the way, I should note that not every artist
(35:40):
who does something synesthetic is actually a synisthet The composer
Scriabin was really interested in the effects of putting sound
and color together, and he thought that would provide a
really strong resonance for the listener. So he invented a
color organ. When you hit the notes, you're not only
(36:00):
playing the musical sound, but there are spotlights of different
colors coming out of the top. But Screopin wasn't actually
a synisthete himself he was just exploring cool things and
was influenced by the fashions of the art world at
that moment. So not everyone who does this sort of
thing is actually a synesthee. And this leads me to
(36:21):
a really important point. How can you tell if someone
really is synesthetic? How can you test for this. So
when someone tells you that they're a synisthete, how could
you ever know if they're just being artistic or metaphorical
or poetic, or lying or just trying to get attention.
(36:42):
So my colleagues and I, over the past fifteen years,
have developed a whole series of tests where we can
show when synesthesia is actually a real perceptual experience. And
I want to tell you how we do that. It
has everything to do with the consistency of people's perceptions.
So if you're a cynisthete who sees eight as lavender,
(37:06):
you're always going to see it as lavender. But if
I were to ask you to make up some colors
right now, and then I ask you again a year
from now, if you're not synesthetic, you're not going to
be able to get these same color associations. But if
you are synesthetic, it'll be the same colors. So many
years ago I launched a website called cinnisthete dot org,
(37:30):
and it's a battery of tests that are freely available.
So if you think you might be a synthete, go
to the site and take the tests. What we can
do this way is rigorously determine who exactly is synesthetic
and who's not. Here's the method. It has anything to
do with internal consistency. So we show you a letter
(37:51):
of the alphabet at random, say a J, and you
see a color palette on the screen, and by moving
a slider around, you can get to any hue, any color,
and by moving a second slider around, you can specify
whatever saturation, in other words, how dark or bright it is.
(38:11):
So you pull the sliders around and you pick the
color that best matches your synesthetic perception for that letter.
And this is out of sixteen million different colors that
can be displayed on a computer screen. And when you
found the best one, you click submit, and then you
get the next random letter or number, say the letter
(38:32):
W or the number three or whatever, and you find
exactly that color that best matches for that one. And
the trick is we present you with each letter and
each number three times, each in random order. So the
idea is that if you are really a synesthee, you're
(38:53):
going to land on the same shade of color for
let's say the letter J every time. And if you're
a sinisthete, it turns out it's very hard to fake that.
So when you look at the results for cynisthetes and
for control subjects who are asked to fake synesthesia, we
can measure the amount of difference in the colors that
(39:14):
they chose. And what we see is that for a
real cinisthete, it's easy. Every time she's presented with the
letter T, she picks the same color or E, it's
the same color every time, and so on. Whereas for
somebody who's asked to use free association or memory or
whatever but they're not actually synesthetic, it's really difficult to
(39:34):
get the same colors. It's a very hard test to
pass to remember what you said fifty seven trials ago
and find that color again out of sixteen million possible colors.
So this turns out to be a powerful way that
we can distinguish who is a cynisthete and who is not.
And we actually have several levels of testing to make
(39:56):
it absolutely impossible to cheat. So, for example, after we've
collected your colors, we then flash it to you on
the screen. So let's say it's the letter H. We
flash an H that's either the color that you've had
chosen or a different color from somewhere else in your palette,
and you have to say as quickly as you can
whether it matches or didn't match your perception. And for
(40:20):
a real cynisthete, if I'm flashing the orange h they'll say, yeah,
that match, and if I flash a green age, they'll
say that doesn't match. But for someone who's just faked
their way through, it's something they're terrible at, both in
terms of accuracy and reaction time. So this is how
we can make sure that we find real cynisthetes. And
(40:43):
we've translated this battery into many different languages, including Chinese
and Hebrew as well as a whole bunch of European languages,
and this way we can find out what's going on
not only in French and Spanish and German, but also
in different alphabetic systems like Cyrillic or Hebrew or Chinese.
Also we can test all sorts of different forms of synesthesia.
(41:05):
And what we have now are about eighteen different forms
of tests, like musical notes to color, or instrument tambers
to color and so on. And it turns out with
this sort of testing we can finally get the sample
sizes that we need, because it turns out that all
the previous literature had a sample size of one. Up
(41:26):
until the early two thousands, it was all single case
studies where people said, hey, I met a cinisthet and
I asked her these questions and here are her answers.
And then people started publishing papers with a participant group
size of two or four, and a few papers had
eight people in them. What we've done now is changed
the game on that because we have rigorously verified over
(41:48):
sixty four thousand cinisthetes and we have their data in
exquisite detail, and this allows us to alter the scientific
playing field. Now, there were a few papers on synesthesia
in the eighteen hundreds, but then synesthesia essentially slipped out
of the scientific spotlight for most of the twentieth century,
(42:09):
and that was because psychology was dominated by the behaviorist
school of thought, where the idea was that we're just
input output reflex machines and it wasn't really appropriate or
scientific to talk about private subjective experience. So as a result,
synesthesia fell to the wayside. But fundamentally, if there's one
(42:32):
thing we know, it's that it feels like something to
have a brain. We have private subjective experience consciousness, and
so as this question has become a serious one in
our field. Synesthesia has risen from the ashes as a
powerful inroad to understanding consciousness. So what causes synesthesia? My
(42:55):
colleagues and I have performed brain imaging and what we
found is that in a cynisthete, neighboring areas of the
brain have a little bit more cross.
Speaker 2 (43:06):
Talk than normal.
Speaker 1 (43:07):
So regions of the brain that care about letters and
numbers happen to be close to other regions that care
about colors, and in a sinisthete, there's a bit more
cross talk between these areas than in a typical brain.
So think of it like two neighboring countries with porous borders.
And some years ago my lab started a long term
(43:29):
project to find the gene or genes that underlie synesthesia.
And to my mind, this is the first step in
a new subfield, which I'm calling perceptual genomics, which just
means understanding the subtle genetic differences that make you see
the world differently than I do. As a scientific community,
(43:51):
we're always looking for the genes for predisposition to diabetes
or aortic stenosis or Parkinson's, or that make some people
taller or broader or red haired or whatever. The same
techniques can be used to find the genes that make
our realities a little different from one another. Something that
(44:12):
struck me, as I mentioned earlier, is that there are
many different subtypes of synesthesia. Now are these all the
same thing or different? In other words, are all synesthesias
due to a single genetic change or are there totally
separate mechanisms involved? So how could I answer this? We
tested all these thousands of people on synesthesia, and we
(44:35):
asked from the data how the different types cluster with
one another. In other words, if you have colored letters,
what is the likelihood that you also have instrument tamber
synesthesia or colored months or colored musical notes or something
like that. How do these different things clump with each other.
(44:56):
What we found is that if you have colored letters
in number, you're really likely to have colored weekdays or months,
but you're not terribly likely to have other forms of
synesthesia like vision to sound or taste to touch. And
what we found is that the different types fall into
five different clusters.
Speaker 2 (45:17):
If you have touch to color.
Speaker 1 (45:20):
You're not really likely to have sound to touch or
other types. They fall into these different groups. And if
you want to know more about this, go to Eagleman
dot com slash podcast to see our different papers on this. Now,
this is an important finding that I'm mentioning because it
suggests that synesthesia is not a single thing genetically, but
(45:41):
there may be at least five different things that we're
all putting under the same umbrella. And the reason we
put them under the same umbrella is simply because they
have something in common. There's a mixture of the senses,
but they might actually be underpinned by different genetic bases.
And this is something I'll talk about in future episodes,
(46:02):
because we're generally seeing the same thing when we look
at other things like schizophrenia. People can present clinically very differently,
but we lump it all under schizophrenia. But I think
it's likely that in ten years from now, we'll talk
about multiple types of schizophrenia, and eventually we'll have totally
new names that identify the different genetic causes that happen
(46:27):
to give rise to these similar conditions that we stick
under the same umbrella. So the one that I've been
concentrating on is the one I call colored sequence synesthesia,
because as I mentioned, the thing to note is that
letters and numbers and weekdays and months are all overlearned sequences.
(46:48):
They're all arbitrary sequences that you memorize when you're about
four or five years old. And the way I started
this genetic study was by crashing a wedding and asking
everyone to spit into spitkits. Now why a wedding, It's
because the whole family tree of this family with synesthesia
was there, so I could march through the tree to
(47:10):
see who has synesthesia and who doesn't, and then do
what's called a family linkage analysis, which looks at how
the small genetic changes march through the family tree and
you find out which tiny changes are tracking with who
has synesthesia. Now, we're still working on this with lots
of different families in their trees, and it may well
(47:32):
be that there are different genetic changes in different families,
but we're getting closer to identifying at least some of
the genes involved. Now, this might involve an increased wiring
in a cineste's brain, or it might involve a slight
imbalance of the inhibition and excitation in the brain such
(47:52):
that you have activity in one area that kindles activity
in the neighboring area. I actually favor the second hypoth
this because non synesthetes can experience synesthesia with drugs, and
people can also experience synesthesia sometimes if they're super tired
and someone slams the door, they'll see colors. Even for synesthetes,
(48:15):
there synesthesia waxes and wanes a bit. Whether they're stressed
or fatigued, or on cigarettes or alcohol, or antidepressants or
anti epileptics. All these things change the quality of their synesthesia.
And that has the feeling of something to do with
the chemical balance, not simply the hardwiring. So I think
(48:36):
that when we find the gene or genes, will be
able to show that it's something associated with the balance
between inhibition and excitation in the brain. So what's amazing
about synesthesia is that what might be a single nucleotide
change in your genome changes the way that you see
the world. It changes the way that you experience and
(49:00):
it's your reality. So this will be the first time
that we're able to say, if you change this little
A or C or T or G over here, now
you are seeing the world differently. Now I want to
ask you a question. I'm going to play two notes
on my piano, which one is brighter, which one is bigger.
(49:26):
I've asked this informally to thousands of nonsynesthes and essentially
everybody answers that the high note is brighter and the
low note is larger. And that's strange, right, because all
I'm doing is playing some notes, and you're mapping that
sound onto brightness and onto size. So what this suggests
(49:48):
is that everyone has some cross connectivity in the brain.
And when you look at the micro anatomy, what you
find is that there are fibers in the brain carrying
visual information that go into the auditory part of your brain,
and there's fibers carrying auditory information that plug straight into
the visual parts of your brain. So this isn't everybody's brain.
(50:11):
It turns out there's naturally a lot of mixing of
the senses, and that's presumably why we all understand expressions
in the language that cross the senses, like oh, that's
a loud tie, or that's cool jazz, or she has
a sweet personality, or that's sharp cheese. Cross sensory expressions
(50:37):
are all over the language, and they kind of work
with everybody.
Speaker 2 (50:41):
We all know what it means when.
Speaker 1 (50:43):
You talk about these So this is the sense in
which we all share something like synesthesia, but we only
call it synesthesia when it's a cross sensory connection. That's rare,
And in this way synesthesia can serve as a terrific
inroad into understanding consciousness, both what people have in common
(51:04):
and what they experience differently. It illustrates a theme that
I'm going to come back to a lot in this podcast,
which is that people can be quite different on the inside. So,
to wrap up today's episode, reality is not one size
fits all. Two people can stand right next to each
other watching the Northern lights, and for one a sound
(51:26):
is internally triggered by the visuals, and not for the other.
Two humans watching the same event and having divergent experiences.
And the important lesson here is that if we're just
trying to understand our own reality, we're like fish in
water trying to describe water. It's impossible to describe what
(51:47):
water is because we've never seen anything other than that.
But when you see a different way that things can be,
that gives you a broader platform from which to build theories,
and that allows us to make progress on one of
our deepest goals in neuroscience to understand how the microscopic
(52:08):
activity in these three pounds of wet, gushy alien computational
material maps onto the world that you see and enjoy
every day, How it maps onto the view that you're
looking at right now, or the feel of your clothes
on your skin, or the sound of my voice in
your ear. That's all for this week. To find out
(52:34):
more and to share your thoughts, head over to eagleman
dot com slash podcasts. If you think you might have
synesthesia and you want to take the tests, go to
sinnisthet dot org. Until next time, I'm David Eagleman, and
this is Inner Cosmos.
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