Michelangelo Buonarroti was once asked to explain how he had crafted one of his most famous sculptures. His well-documented reply was honest, simple and accurate: "I saw the angel in the marble and carved until I set him free."
The Renaissance Italian genius was first and foremost an artisan who had learnt the craft of sculpture from his elders. But that fails to explain how he "saw" a non-existent celestial figure in a lump of marble with such clarity that he could create its image in three dimensions.
The concept of imagination remains one of the greatest uncharted territories of psychology. Granted, we can't all paint the ceiling of the Sistine Chapel, but almost all of us have an ability to come up with ideas or images. So it's time scientists paid more attention to the power of imagination, said Open University senior psychology lecturer Dr Ilona Roth.
"The problem is that psychologists have either studied individual aspects of imagination piecemeal or have avoided the topic altogether," she said. "It features in several branches of psychology but no research seems to tie it all together."
Certainly some early psychologists thought the imagination wasn't susceptible to scientific study. Behaviour theorists such as John B Watson, who saw human behaviour as learnt responses to an environment, refused to research the concept because they could not observe it.
"Some contemporary psychologists see imagination as imagery: visual-type experiences in your head without any sensory input," said Dr Roth. "Others focus on pretence, fantasy, or creativity. Others look at 'social' imagination and empathy. Still others link it to counter-factual reasoning - 'what if?'. Imagination means different things to different people, so maybe psychologists are right not to put it all together. But while psychologists are skirting the territory, researchers in other disciplines are seizing many of the initiatives. We need dialogue - not only among psychologists but with researchers in other fields."
Dr Roth recently demonstrated the scope for such a fusion of approaches when she hosted Imaginative Minds, a symposium on the subject at the British Academy in London. It proved, she claims, that imagination can be valuably researched in a variety of disciplines, not least evolutionary studies and archaeology.
"Our distant ancestors undoubtedly had forms of imagination," she said. "Tool making, the capacity to hunt and to live in social groups all required it."
But researchers into imagination disagree about the nature of its history. It's a common, though not uncontested, belief that between 20,000 and 50,000 years ago mankind experienced a "symbolic explosion", resulting in the first decorative art. "People were creating things for more than functional purposes," said Dr Roth. "They made them attractive or even created artifacts with a primarily decorative purpose."
This explosion heralded such imaginative creations as the famous French cave paintings in Lascaux and Vallon Pont D'Arc and bequeathed an artistic, inventive legacy that has influenced every aspect of our lives. But it doesn't follow that with 50 millennia of imagination behind us, this 21st century will herald a golden age of creativity.
"We have greater stimulus than ever," said Dr Roth. "But some would say certain aspects of our culture suppress the imagination. There's a risk that modern technology - TV, computer games - stifles imagination by supplying the images a child would otherwise work to create in its mind. That said, IT can be a wonderful inspiration. Computers are bringing more imagination than ever into, say, maths teaching. The key is to get children actively engaged."
Not everyone can be a Picasso but it seems we do all have a talent for mental pictures. One of Dr Roth's research interests is autistic children, who are usually thought to lack creativity. "It's true such children will play unimaginatively - while others use building blocks to make things, the autistic children will lay them in a row," she said. "They are capable of less pretence than others. But some forms of visual imagery function rather well in autism."
Then there is the one in 200 autistic children with so-called savant skills. At the age of 12, Stephen Wiltshire astonished a nationwide television audience by drawing a detailed architectural sketch of St Pancras station entirely from memory. The BBC show, entitled The Foolish Wise Ones, prompted a wealth of commissions and enabled Wiltshire, now 29, to make a living from his talent. There are others, too. An English girl known only as Nadia could draw exceptional sketches of horses at the age of three. Richard Wawro, who exhibited his autism in childhood by walking in circles and striking a piano key for hours at a time, did not talk until the age of 11 - now 52, he has sold 1,000 paintings, almost all recreations of images he has seen only once.
"There is discussion as to whether such people are truly creative," said Dr Roth. "Stephen Wiltshire is a fantastic artist but some would argue that what he does is more reproductive than imaginative. Then again, Richard Wawro's pictures are so vivid and idiosyncratic, how can you square that with the idea they are not imaginative?"
Atypical brain function can certainly affect imagination. Some psychologists claim to have found a disproportionate link between creativity and mental illness. Dr Roth is quick to stress a propensity for one does not automatically lead to the other but accepts there may be a connection. "The genealogies of Byron and Tennyson show mental disorder, and they suffered from depression," she said. "Virginia Woolf was a manic depressive. So was Spike Milligan. Even people with early stage Alzheimer's can show increased creativity. This suggests an enhancement of some neural mechanisms at the expense of others."
But however imagination manifests itself, inventors need discipline to hone their creations into objects of usefulness. Shakespeare broke many boundaries but was a master of the tightly structured plot.
"Mental fluidity needs constraint," said Dr Roth "Without it, you have free association, which leads to chaos. Your imagination literally runs away with you.
"Because of the traditional link between imagination and 'flights of fancy', there's been a lingering belief that imagination doesn't have much to do with science. But imagination is just as important in science as in the arts."
Even the world's greatest scientists might agree with that. After all, "knowledge is limited" once wrote no less a figure than Albert Einstein. "But imagination encircles the world."
To test your creativity and imagination, visit the Imaginative Minds website at www.britac.ac.uk/events/imagination/ and click on "additional resources". For details of OU psychology courses, visit www.open.ac.uk/coursesReuse content