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Imagine a world

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in which you see numbers and letters as colored

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even though they're printed in black,

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in which music or voices trigger a swirl

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of moving, colored shapes,

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in which words and names fill your mouth

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with unusual flavors.

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Jail tastes like cold, hard bacon

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while Derek tastes like earwax.

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Welcome to synesthesia,

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the neurological phenomenon

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

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A synesthete might not only hear my voice,

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but also see it,

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taste it,

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or feel it as a physical touch.

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Sharing the same root with anesthesia,

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meaning no sensation,

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synesthesia means joined sensation.

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Having one type, such as colored hearing,

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gives you a 50% chance of having a second,

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third,

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or fourth type.

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One in 90 among us experience graphemes,

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the written elements of language,

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like letters,

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numerals,

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and punctuation marks,

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as saturated with color.

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Some even have gender or personality.

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For Gail, 3 is athletic and sporty,

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9 is a vain, elitist girl.

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By contrast, the sound units of language,

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or phonemes,

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trigger synestetic tastes.

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For James, college tastes like sausage,

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as does message and similar words

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with the -age ending.

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Synesthesia is a trait, like having blue eyes,

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rather than a disorder

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because there's nothing wrong.

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In fact, all the extra hooks

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endow synesthetes with superior memories.

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

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

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D's are green:

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Debra,

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Darby,

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Dorothy,

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Denise.

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Yes! Her name is Denise!"

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Once established in childhood,

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pairings remain fixed for life.

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Synesthetes inherit a biological propensity

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for hyperconnecting brain neurons,

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but then must be exposed to cultural artifacts,

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such as calendars,

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food names,

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and alphabets.

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The amazing thing is that a single nucleotide change

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in the sequence of one's DNA alters perception.

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In this way, synesthesia provides a path

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to understanding subjective differences,

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how two people can see the same thing differently.

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Take Sean, who prefers blue tasting food,

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such as milk, oranges, and spinach.

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The gene heightens normally occurring connections

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between the taste area in his frontal lobe

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and the color area further back.

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But suppose in someone else

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that the gene acted in non-sensory areas.

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You would then have the ability to link

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seemingly unrelated things,

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which is the definition of metaphor,

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seeing the similar in the dissimilar.

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Not surprisingly, synesthesia is more common

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in artists who excel at making metaphors,

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like novelist Vladimir Nabokov,

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painter David Hockney,

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and composers Billy Joel

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and Lady Gaga.

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But why do the rest of us non-synesthetes

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understand metaphors like "sharp cheese"

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or "sweet person"?

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It so happens that sight,

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sound,

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and movement

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already map to one another so closely,

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that even bad ventriloquists convince us

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that the dummy is talking.

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Movies, likewise, can convince us

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that the sound is coming from the actors' mouths

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rather than surrounding speakers.

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So, inwardly, we're all synesthetes,

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outwardly unaware of the perceptual couplings

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happening all the time.

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Cross-talk in the brain is the rule,

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not the exception.

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And that sounds like a sweet deal to me!