in which you see numbers and letters as colored

even though they're printed in black,

in which music or voices trigger a swirl

of moving, colored shapes,

in which words and names fill your mouth

with unusual flavors.

Jail tastes like cold, hard bacon

while Derek tastes like earwax.

Welcome to synesthesia,

the neurological phenomenon

that couples two or more senses in 4% of the population.

A synesthete might not only hear my voice,

but also see it,

taste it,

or feel it as a physical touch.

Sharing the same root with anesthesia,

meaning no sensation,

synesthesia means joined sensation.

Having one type, such as colored hearing,

gives you a 50% chance of having a second,

third,

or fourth type.

One in 90 among us experience graphemes,

the written elements of language,

like letters,

numerals,

and punctuation marks,

as saturated with color.

Some even have gender or personality.

For Gail, 3 is athletic and sporty,

9 is a vain, elitist girl.

By contrast, the sound units of language,

or phonemes,

trigger synthetic tastes.

For James, college tastes like sausage,

as does message and similar words

with the -age ending.

Synesthesia is a trait, like having blue eyes,

rather than a disorder

because there's nothing wrong.

In fact, all the extra hooks

endow synesthetes with superior memories.

For example, a girl runs into someone she met long ago.

"Let's see, she had a green name.

D's are green:

Debra,

Darby,

Dorothy,

Denise.

Yes! Her name is Denise!"

Once established in childhood,

pairings remain fixed for life.

Synesthetes inherit a biological propensity

for hyperconnecting brain neurons,

but then must be exposed to cultural artifacts,

such as calendars,

food names,

and alphabets.

The amazing thing is that a single nucleotide change

in the sequence of one's DNA alters perception.

In this way, synesthesia provides a path

to understanding subjective differences,

how two people can see the same thing differently.

Take Sean, who prefers blue tasting food,

such as milk, oranges, and spinach.

The gene heightens normally occurring connections

between the taste area in his frontal lobe

and the color area further back.

But suppose in someone else

that the gene acted in non-sensory areas.

You would then have the ability to link

seemingly unrelated things,

which is the definition of metaphor,

seeing the similar in the dissimilar.

Not surprisingly, synesthesia is more common

in artists who excel at making metaphors,

like novelist Vladimir Nabokov,

painter David Hockney,

and composers Billy Joel

and Lady Gaga.

But why do the rest of us non-synesthetes

understand metaphors like "sharp cheese"

or "sweet person"?

It so happens that sight,

sound,

and movement

already map to one another so closely,

that even bad ventriloquists convince us

that the dummy is talking.

Movies, likewise, can convince us

that the sound is coming from the actors' mouths

rather than surrounding speakers.

So, inwardly, we're all synesthetes,

outwardly unaware of the perceptual couplings

happening all the time.

Cross-talk in the brain is the rule,

not the exception.

And that sounds like a sweet deal to me!