Were your grandparents mentally retarded? What is it that people enjoy about an expensive meal? In what way are dogs and rabbits alike? And what happens when you inject Pepsi into someone's mouth while they are hooked up to a functional magnetic resonance imaging machine?

Sit back and I'll answer all these questions. And explain how they give you a crucial insight into Gordon Brown's difficulties.

I suspect our Prime Minister is rather puzzled. For years, all he heard were complaints about Tony Blair's spinning. So he set out to present himself as more straightforward and it has been a spectacular failure. We seemed so scathing about Blair's PR machine, but now we are even more critical of Mr Brown's poor presentational skills. Perhaps Gordon is wondering what exactly it is we are all after.

Yet he would be wrong to be bewildered. It is true that people became bored with Mr Blair, and felt frustrated that the press releases and claims of success seemed to run so far ahead of the reality. But the idea that people no longer wanted big themes and a clear and coherent narrative was a misunderstanding.

Presenting people with a series of unconnected policy initiatives is never going to work, even if each is a populist masterpiece designed by a genius. When, a genius being unavailable, they are instead designed by Ed Balls, Labour's bill for election night champagne is likely to remain small.

The Prime Minister cannot just put his head down and power on, hoping that voters will be impressed by the reality of Brown's Britain. And he wouldn't be able to even if the reality of Brown's Britain was better than it is. Because the head-down, concentrate-on-the-detail approach ignores the way that people think.

In his compelling new book Predictably Irrational the behavioural economist Dan Ariely reports on a series of experiments designed to test the impact that perception has upon reality. Professor Ariely, for instance, laced beer with balsamic vinegar and discovered that respondents believed that it made the brew taste better, unless, that is, they were told about the added ingredient. Those informed in advance about the vinegar really disliked the beer.

A test using coffee demonstrated that consumers were prepared to pay more and enjoyed their drink more when fancy coffee was placed in a fancy container rather than a Styrofoam cup. Expensive meals and expensive wine works in the same way. Instead of being cross at receiving a meal that could have been cheaper, we change our view of the reality to match the price. We really do enjoy it more.

An extraordinarily elaborate piece of lab work involving a resonance imaging machine and injecting Coke and Pepsi into the mouths of subjects demonstrates clearly that the line between perception and reality is blurred. When people received a squirt of the two drinks, the machine registered very similar brain activity. But when told that they were tasting Coke, there was enhanced activity in the brain's pleasure centre.

The image of a product like Coke is not separate from the way it is experienced. Similarly, the way policies are explained and linked together, the story that is told about them and the brand image of the party advancing them affects the way those policies are experienced. Perception and reality, spin and delivery, style and substance are woven together.

Is this depressing? A symbol that we are becoming shallower and more easily fooled? Final proof that we are dumbing down? Quite the opposite. It is the result of an undeniable fact about human beings - we aren't dumbing down, we are dumbing up. We are becoming smarter.

In another recently published book, What is Intelligence?, James Flynn analyses what has become known as the Flynn Effect. This is the name that has been given to the professor's observation that intelligence testing reveals that during the 20th century there have been massive gains in IQ, gains not explained by changes in the method of testing.

Professor Flynn had been concerned about a troubling implication of his theory: if, given trends in IQ, you look backwards, the figures seem to suggest that our grandparents and great grandparents were, to use the unlovely designation common in that era, mentally retarded. This seemed to him unlikely, so he referred to it as the mental retardation paradox.

In his new book, Professor Flynn thinks he has discovered the answer. Our performance, on average, in IQ tests hasn't improved across the board. In some tasks we are no better than in days gone by, in others we have hugely improved. Our store of information, our arithmetic and our vocabulary are hardly changed. What has become much better is our ability to match symbols with numbers, to rearrange scrambled picture cards to tell a story and to classify things (for instance, a rabbit and a dog are both mammals).

Our ancestors, living in an era before mass communication and in a pre-scientific age, did not have the same requirement that we now have to understand things that we haven't directly experienced. They managed just fine with their concrete forms of thinking (a dog hunts a rabbit) about the world they lived in. They were not mentally retarded in the slightest. It is simply that the average person had less need and thus less aptitude for abstract thought, classification, assembling narratives and solving problems they had never encountered before.

These are habits of mind of the modern age. We have, Professor Flynn suggests, changed our way of thinking and in doing so become more intelligent. I would also suggest that it imposes a requirement on politicians to able to explain themselves, to have a strong narrative, to advance big themes.

Tony Blair was supremely capable of such exposition. Gordon Brown is lamentably bad at it. I suspect he believes that salvation lies in eschewing altogether something he is not very good at. If this is his hope, I think he is likely to be sorely disappointed.

daniel.finkelstein@thetimes.co.uk

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