and long after that,

scientists and philosophers alike

have puzzled over what they call the mind-body problem.

Is the mind some separate, non-material entity piloting a machine of flesh?

Or if it's just a particularly elusive part of our physical body,

how can it translate the input of our animal senses

into the seemingly non-physical experiences that we call thoughts?

But though the answers have been debated endlessly,

new research suggests that part of the problem lies

in how we pose the question in the first place,

assuming a distinction between our sensory perception and our ideas

that may not really be there.

The traditional model of our mental function

has been that the senses provide separate data to our brain

which are then translated into the appropriate mental phenomena:

visual images into trees, auditory experiences into bird songs, and so on.

But occasionally, we have come across people

whose senses seem to mingle together, allowing them to hear colors,

or taste sounds.

Until recently, the common understanding was that this phenomenon,

called synesthesia,

was a direct connection between the parts of the brain

responsible for sensory stimuli such as

seeing the color yellow immediately upon hearing the tone of b flat.

But newer studies have shown that synesthesia

is actually mediated through our understanding

of the shapes, colors and sounds that our senses apprehend.

In order for the cross-sensory experiences to occur,

the higher level ideas and concepts that our minds associate

with the sensory input must be activated.

For example, this shape can be seen as either the letter "s" or the number "5"

and synesthetes associate each with different colors or sounds

based on how they interpret it

despite the purely visual stimulus remaining identical.

In another study, synesthetes created novel color associations

for unfamiliar letters after learning what the letters were.

So because it relies on a connection between ideas and senses,

this mental phenomenon underlying synesthesia

is known as ideasthesia.

Synesthesia only occurs in some people,

although it may be more common than previously thought.

But ideasthesia itself is a fundamental part of our lives.

Virtually all of us recognize the color red as warm and blue as cold.

Many would agree that bright colors, italic letters and thin lines

are high-pitched,

while earth tones are low-pitched.

And while many of these associations are acquired through cultural exposure,

others have been demonstrated even in infants and apes,

suggesting that at least some associations are inborn.

When asked to choose between two possible names for these shapes,

people from entirely different cultural and language backgrounds

overwhelmingly agree that "kiki" is the spiky star,

while "bouba" is the rounded blob,

both because of the sounds themselves and the shapes our mouths make

to produce them.

And this leads to even more associations

within a rich semantic network.

Kiki is described as nervous and clever,

while bouba is perceived as lazy and slow.

What all of this suggests is that our everyday experiences

of colors, sounds and other stimuli do not live on separate sensory islands

but are organized in a network of associations

similar to our language network.

This is what enables us to understand metaphors

even though they make no logical sense,

such as the comparison of snow to a white blanket,

based on the shared sensations of softness and lightness.

Ideasthesia may even be crucial to art,

which relies on a synthesis of the conceptual and the emotional.

In great art, idea and aesthesia enhance each other,

whether it's song lyrics combining perfectly with a melody,

the thematic content of a painting

heightened by its use of colors and brushstrokes,

or the well constructed plot of a novel

conveyed through perfectly crafted sentences.

Most importantly, the network of associations formed by ideasethesia

may not only be similar to our linguistic network

but may, in fact, be an integral part of it.

Rather than the traditional view,

where our senses first capture a collection of colors and shapes,

or some vibrations in the air,

and our mind then classifies them as a tree or a siren,

ideasthesia suggests that the two processes occur simultaneously.

Our sensory perceptions are shaped by our conceptual understanding of the world.

and the two are so connected that one cannot exist without the other.

If this model suggested by ideasthesia is accurate,

it may have major implications for some of the biggest

scientific and philosophical issues surrounding the study of mind.

Without a preexisting concept of self,

Descartes would not have had an "I" to attribute the thinking to.

And without a preexisting network of interrelated and distinct concepts,

our sensory experience of the world would be an undifferentiated mass

rather than the discrete objects we actually apprehend.

For science, the task is to find where this network lies,

how it is formed, and how it interacts with external stimuli.

For philosophy, the challenge is to rethink

what this new model of consciousness means for our understanding of our selves

and our relation to the world around us.