Why some see colours in numbers

US scientists say they can explain why some people 'see' colours when they look at numbers and letters. As many as one in 2,000 people has an extraordinary condition in which the five senses intermingle, called synaesthesia.

The study in Neuron tracked the brain activity of people with the most common form and found peaks in areas involved with perceiving shapes and colours.

The University of California San Diego team said their findings lend support to the idea that the condition is due to cross-activation between adjacent areas of the brain involved with processing different sensory information.

This cross-wiring might develop, they believe, by a failure of the "pruning" of nerve connections between the areas as the brain develops while still in the womb.

For example, a person with synaesthesia might see red when they look at an ordinary figure '5' drawn in black ink on a white background because the red colour perception area of their brain is stimulated at the same time as the number recognition area.

The researchers conducted a series of experiments on volunteers with and without synaesthesia.

When the people without synaesthesia looked at letters and numbers only the brain areas involved with processing this information light up on brain activity scans.

In comparison, the people with synaesthesia had activity in colour perception regions as well.

Furthermore, some of the people with synaesthesia appeared to be better at 'seeing' colours than the others.

Those who had stronger colour perception had more activity in their colour perception brain areas.

Researcher Vilayanur Ramachandran said processes similar to synaesthesia might also underlie our general capacity for metaphor and be critical to creativity.

"It is not an accident that the condition is eight times more common among artists than the general population."

Dr Julia Simner, who has been studying synaesthesia at the University of Edinburgh along with colleagues at University College London, said the findings were supported by similar work looking at people who see colours when they hear sounds.

"Interestingly, we've recently analysed the letter-colour combinations of a very large number of people with synaesthesia and found that there are significant trends in their preferences.

"For example, people with synaesthesia tend to want A to be red, S to be yellow and Z to be black."

She said her research also revealed that people without synaesthesia have significant preferences for the colours of letters.

"Some of these choices were fairly obvious, such as 'O' being orange, but some were quite intriguing, and showed a similarity to those of people with synaesthesia."

Her findings are currently in press to appear in the journal Cognitive Neuropsychology.

Jennifer Green from the University of Cambridge, who has also been carrying out research in this area, said: "Some describe seeing the colours induced by letters and numbers as projected externally into space, while others report experiencing them internally, or in their 'mind's eye'.

"This research lends further support to empirical evidence suggesting that these varying descriptions represent actual differences in the way synaesthesia occurs in individuals."

The Romantic poets valued synaesthesia. Consider the mixture of the five senses in Keats's "Ode to a Nightingale," and notice the confusion of the various senses in Stanza 5, especially, as the sound of the nightingale evokes sight and scent, taste and touch:

40. Ode to a Nightingale

1.

MY heart aches, and a drowsy numbness pains
My sense, as though of hemlock I had drunk,
Or emptied some dull opiate to the drains
One minute past, and Lethe-wards had sunk:
’Tis not through envy of thy happy lot, 5
But being too happy in thine happiness,—
That thou, light-winged Dryad of the trees,
In some melodious plot
Of beechen green, and shadows numberless,
Singest of summer in full-throated ease. 10

2.

O, for a draught of vintage! that hath been
Cool’d a long age in the deep-delved earth,
Tasting of Flora and the country green,
Dance, and Provencal song, and sunburnt mirth!
O for a beaker full of the warm South, 15
Full of the true, the blushful Hippocrene,
With beaded bubbles winking at the brim,
And purple-stained mouth;
That I might drink, and leave the world unseen,
And with thee fade away into the forest dim: 20

3.

Fade far away, dissolve, and quite forget
What thou among the leaves hast never known,
The weariness, the fever, and the fret
Here, where men sit and hear each other groan;
Where palsy shakes a few, sad, last gray hairs, 25
Where youth grows pale, and spectre-thin, and dies;
Where but to think is to be full of sorrow
And leaden-eyed despairs,
Where Beauty cannot keep her lustrous eyes,
Or new Love pine at them beyond to-morrow. 30

4.

Away! away! for I will fly to thee,
Not charioted by Bacchus and his pards,
But on the viewless wings of Poesy,
Though the dull brain perplexes and retards:
Already with thee! tender is the night, 35
And haply the Queen-Moon is on her throne,
Cluster’d around by all her starry Fays;
But here there is no light,
Save what from heaven is with the breezes blown
Through verdurous glooms and winding mossy ways. 40

5.

I cannot see what flowers are at my feet,
Nor what soft incense hangs upon the boughs,
But, in embalmed darkness, guess each sweet
Wherewith the seasonable month endows
The grass, the thicket, and the fruit-tree wild; 45
White hawthorn, and the pastoral eglantine;
Fast fading violets cover’d up in leaves;
And mid-May’s eldest child,
The coming musk-rose, full of dewy wine,
The murmurous haunt of flies on summer eves. 50

6.

Darkling I listen; and, for many a time
I have been half in love with easeful Death,
Call’d him soft names in many a mused rhyme,
To take into the air my quiet breath;
Now more than ever seems it rich to die, 55
To cease upon the midnight with no pain,
While thou art pouring forth thy soul abroad
In such an ecstasy!
Still wouldst thou sing, and I have ears in vain—
To thy high requiem become a sod. 60

7.

Thou wast not born for death, immortal Bird!
No hungry generations tread thee down;
The voice I hear this passing night was heard
In ancient days by emperor and clown:
Perhaps the self-same song that found a path 65
Through the sad heart of Ruth, when, sick for home,
She stood in tears amid the alien corn;
The same that oft-times hath
Charm’d magic casements, opening on the foam
Of perilous seas, in faery lands forlorn. 70

8.

Forlorn! the very word is like a bell
To toil me back from thee to my sole self!
Adieu! the fancy cannot cheat so well
As she is fam’d to do, deceiving elf.
Adieu! adieu! thy plaintive anthem fades 75
Past the near meadows, over the still stream,
Up the hill-side; and now ’tis buried deep
In the next valley-glades:
Was it a vision, or a waking dream?
Fled is that music:—Do I wake or sleep? 80

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