The Globe

This is why we can get the words of songs completely wrong and not realise it. The Guardian newspaper ran an amusing section on this habit, with examples such as 'kit-kat angel' for 'kickass angel' - bit of a generation gap there, which underlines how our perceptions are biased by our expectations. Ian recalls an A

Holding a whole sentence, or a musical phrase, in our minds is what we do with time when we watch a TV or a cinema-screen. We run the frames together into a series of scenes, as well as making up all the spatial stuff that we're not actually looking at. The brain has so many tricks that its owner is not conscious of: as you sit there in the cinema your eyes are flicking from place to place on the screen, as they are doing while you read these words. But you turn off your perception as your eyes move, and re-jig your invented image so that your next retinal image is consistent with the previous version. That's why you get seasick or car-sick: if the outside image jumps about and isn't where you expect it to be, then that upsets your sense of balance.

Now think about a piece of music. Isn't the construction of an extended present precisely the exercise that your brain 'wants' to do with a series of sounds, but without the complication of the meanings! As soon as you get used to the style of a particular kind of music, you can listen to it and grasp whole themes, tunes, developments, even though you're hearing only one note at a time. And the instrumentalist who is making the noise is doing the same kind of thing. His brain has expectations of what the music should sound like, and he fulfils those. To some extent.

So it seems that our sense of music may be tied to a sense of an extended present. Some possible scientific evidence for this proposition has recently been found by Isabelle Peretz. In 1977 she identified a condition called 'congenital amusia'. This is not tone-deafness, but tune-deafness, and it should give us some insight into how normal people recognise tunes, by showing how that goes wrong. People with this condition ca

The same kind of interpretational step takes place in the visual arts, too. When you look at a painting -a Turner, say -it evokes in you a variety of emotions, perhaps nostalgia for a nearly forgotten holiday on a farm. That may give you a little burst of endorphins, chemicals in the brain that create a sense of well-being, but presumably you'd get much the same from a photograph or even a verbal description or a bit of pastoral poetry. The Turner painting does more than that, perhaps because it can be more sentimental, more idealised than a photo, however idyllic. It evokes the memory on a more personal level.

What about other kinds of painting: the paper textures, the charcoal smear? Jack went to an art gallery, as an i

Art goes back a long, long way, the further back we look, the more controversial the evidence is.

The 'Dame a la Capuche', a 1.5-inch (3.5-cm) high statuette of a woman, exquisitely carved from mammoth-tusk ivory, is 25,000 years old. Some of the most elegant cave paintings, with simple, sweeping lines that depict horses, bison and the like, are found in the Grotte Chauvet in France, and in 1995 they were dated at 32,000 years old. The oldest art that undoubtedly is art is about

38,000 years old: beads and pendants, found in Russia. And some beads made from ostrich egg shells in Kenya, which may be 40,000 years old.

Further back, it all gets less certain. Ochre is a common pigment in rock drawings, and ochre

'crayons' found in Australia are 60,000 years old. There is a lump of rock from the Golan Heights, whose natural crevices have been worn deeper, presumably by a human hand wielding another lump of rock. It bears a vague resemblance to a woman, and it is about 250,000 years old. But maybe it's just a lump of rock that a child idly scratched, and the shape is accidental.

Imagine yourself in the cave as the artist paints bison on the wall. He (or she?) is creating a picture for your brain that differs progressively from the one that your brain expects: 'Now let's put a female woolly rhinoceros under him ...' There have been several 'artists' on television, doing precisely that trick. Rolf Harris was surprisingly good at drawing animal sketches before your very eyes. And they were iconic animals, too: sly fox and wise owl.

There it all is, tied up in a bundle. Our perceptions are tied to our expectations, and we do not segregate sensations from each other, or from memories. They are all played off against each other in the seclusion of our minds. We absolutely do not program our brains with direct representations of the real world. From the begi

That's what our brains do, and what edge people's brains don't.

We suspect that Neanderthals didn't do that kind of thing much, either, because there's an alternative, and it's consistent with their cultural torpor. The alternative is to live in a world that you've set up to ensure that nothing is unexpected. All the events follow your expectations from previous events, so habit engenders security. Such a world is very stable, and that means it doesn't go anywhere much. Why try to leave the Garden of Eden? Gorillas don't.

Tribal life could be like that for Homo sapiens, except that reality always intrudes, for instance those barbarians up on the hill. But Neanderthals, maybe, weren't afflicted by barbarians.

Certainly, nothing seems to have provoked big changes in their lifestyles, even over tens of thousands of years. Art does provoke changes. It makes us look at the world in new ways. The elves like that, it gives new ways for them to terrify people. But Rincewind has seen further than the elves are capable of seeing, and he's worked out where art takes us. Where? You'll soon find out.