Science: More real than the real thing: Snow on television makes them shiver; taking a shower can plunge them into an imaginary tropical glade. John McCrone on new research into why some women fantasise more vividly than others

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PERHAPS as many as one in 25 people harbour a secret. They have a fantasy life that is far more vivid than that experienced by the rest of us. For the majority of people, mental images are pale and fleeting things. But for some reason it appears a few people are able to conjure up experiences, complete with smells, sounds and body sensations, which are almost hallucinatory in their detail.

An American researcher, Dr Sheryl Wilson, examined a group of 27 women who all happened to be excellent hypnotic subjects. She wondered what the women might have in common and found that the reason they were able to lose themselves so readily in a hypnotic trance state was that they already spent most of their days immersed in imaginary realities of their own making.

To the outside world the women appeared to be living normal lives. But in interviews they claimed to have parallel lives where the sight of a passing bird would set them soaring through the air as if they had been transformed into a bird themselves; or stepping into a humble bathroom shower would become transformed into plunging into a waterfall in a tropical glade.

The women said more than half their days were spent in such elaborate fantasy settings - indeed, most found it easier to estimate how many hours a day were not spent in a fantasy world. Naturally enough, sex featured strongly in their day-dreams. Most described the sex as being 'as real as real', complete with orgasm - the difference being that their lovers were rather more interesting than usual.

Self-reports of mental phenomena are notoriously poor evidence in psychological research. But what convinced Wilson that the women shared a genuine ability was the similarity of the comments they made in separately conducted interviews. Many said they had to make it a conscious rule not to fantasise while doing something that demanded their full attention, such as driving - although several said they actually used special images to help them stay focused on the road ahead, such as projecting four small protective angels at each corner of the car or imagining it bathed in a bright light.

The women also had similar childhood stories. Most had a lonely or unhappy upbringing and learnt to use their imaginations as an escape. All had fantasy companions, one having 24 imaginary friends. They also learnt to conceal their fantasy lives at an early age. One girl had convinced herself she was a princess living in a castle, and was rather hurt when she brought a friend home and found the friend could not see its grand castle walls.

As adults, 60 per cent of the women had had phantom pregnancies - two going as far as booking themselves in for abortions. Watching violent scenes on television made all the women physically ill. They would become so caught up in what they were watching that they would have to bundle up in blankets to view snowy scenes in films such as Dr Zhivago.

Wilson says it is difficult to know how many other people may share such an intense form of imagination. However, she argues that with about 4 per cent of the population falling into the category of excellent hypnotic subjects, the figure may be as high as one in 25.

The problem with research such as Wilson's is that it depends on anecdotal evidence and until quite recently, few psychologists would have treated it as serious proof that people can have exceptional imaginations. For most of this century, a surprising number of mainstream psychologists have questioned whether mental images exist at all.

The controversy dates back to a simple thought experiment carried out by Sir Francis Galton in the 1880s. Galton asked people to imagine what they had had for breakfast and found that although 'common working folk', as he put it, believed they inspected a mental image, many of his eminent scientist friends insisted that they experienced no pictures in their minds whatsoever. They said their thinking was purely verbal and abstract. This inspired the view that people claiming to have imagery must either be deluding themselves, or else they were exhibiting a more primitive, child-like thought style that rational Victorian males had long left behind.

Between the 1920s and the 1960s, with the Behaviourist movement ruling that mental events could not be the subject of proper scientific enquiry, little further research was done on imagery. Cognitive psychology, which replaced Behaviourism as psychology's dominant school in the 1970s, managed to put mental events back on to the agenda. But because the cognitive approach assumed that the human mind was pretty much like a computer - a symbol-processing machine running abstract programs - psychologists felt that the idea of having little pictures in the head was logically impossible.

Some, such as Zenon Pylyshyn from the University of Western Ontario, went as far as arguing that our feeling of having images was probably just a complicated illusion. After all, Pylyshyn argued, it could be simply part of some people's mental programming that makes them claim that they have images. Since there seems no way of objectively proving whether a person is genuinely experiencing an image, or merely making a deluded claim, then the simplest - and therefore the most scientifically correct - approach is to assume that images do not exist.

Of course, to most people such a denial of imagery seems ridiculous. Not everyone may have especially bright imagery and often the experience of imagining is, as the philosopher Gilbert Ryle put it, not that of being the 'spectator of a resemblance', but rather of 'resembling being a spectator'. That is, it takes a certain effort to conjure up an impression and usually the image shifts unsteadily, lasting only an instant and evaporating as soon as we try to fix our attention on it. It is only in rare cases, such as Wilson's study group, that people claim their imagery is persistent and powerful enough to block out the outside world. Yet even if most of us experience imagery that is fleeting and unstable, we are still pretty sure something is there.

Fortunately, in the past few years there has been a great turnaround in psychological research prompted by the arrival of brain-scanning technology that can 'film' the human brain as it thinks. These multi-million pound scanners, originally built as tools for diagnosing cancers and other medical conditions, can pick up the minute electrical fields and blood flows generated when the brain sets to work. Brain scanners allow psychologists to ask a person an imagination-stimulating question such as: 'Is the green of a pine tree darker or lighter than the green of grass?' and then see how the brain responds, for the first time giving direct evidence of what happens in our heads as we form an image.

One of the most comprehensive of the studies carried out so far was published earlier this year by a team headed by a Harvard University

professor, Stephen Kosslyn. Among other things, the study may provide a clue as to why some people might have more powerful imagery than others. Kosslyn asked his subjects to project a mental image of a letter on to a grid marked out on a computer display in front of them. Then, in a second set of trials, the subjects simply watched a computer-generated letter and grid. By subtracting the 'imagery' condition from the baseline 'perception' condition, Kosslyn could see which regions of the brain lit up in doing the task.

Kosslyn's most significant finding was that imagining a letter generated a pattern of activity in the visual areas of the brain that was a close match for the activity which occurred when subjects were actually shown a letter on the grid. This demonstrated clearly what many psychologists have long suspected, but could not prove - that the act of imagining is much like an inwardly-stimulated act

of vision. We make use of the same perceptual pathways for both seeing and imagining.

Furthermore, Kosslyn says the brain scans showed that our mental images are topographically represented in the brain - they are spatially arranged maps and not abstract, computer-like programs as argued by many cognitive psychologists. The most convincing proof of this came from asking subjects to imagine letters of different sizes. When subjects were asked to imagine a small letter, only the centre of their coin-sized visual cortexes were activated. But when they were asked to imagine that the letter nearly filled their fields of vision, neural activity stretched almost to the edge of the visual zone.

'The people working in cognitive science and artificial intelligence have been completely opposed to the notion that we can have any real picture-like structures in our heads, and so have found this evidence totally surprising. I have shown slides from these experiments at a few conferences recently, and there has been just stunned silence from the audience. That's been kind of fun,' says Kosslyn, laughing.

As to why some people might have exceptionally vivid imagery, Kosslyn says an interesting finding was that one particular patch of brain surface right on the edge of the primary visual cortex appears to be particularly active when we imagine. It appears that this region may be an override mechanism that allows us to suppress the visual zone's normal traffic of perceptual images and instead 'display' mental images taken from memory.

Despite the attractiveness of the hypothesis, Kosslyn is cautious, saying more subtle explanations are possible. However, the difference now is that psychologists can test such an idea. Kosslyn says a new brain scanner system being built by a team at Helsinki University of Technology has a far greater resolution than systems presently in use and will be able to measure the difference between people with average-strength and super-strength imagery.

'The Helsinki group has already done some preliminary work which shows that, when you find imagery activity in the visual cortex of a person, you really find it - there are definite individual differences. Obviously, the next step is to start looking at what makes the difference. In the past, there has been a lot of speculation about how imagery and perception are related. Now we have the techniques to begin to characterise the relationship,' says Kosslyn.

John McCrone writes about imagination, dreams and thought in 'The Myth of Irrationality: The Science of the Mind From Plato to Star Trek' (Macmillan pounds 16.99).

(Photograph omitted)