The Science of Discworld II

ourselves the illusion that we’re seeing about ninety degrees of arc. We perceive an extended version of the tiny region that our senses are detecting. Similarly, when we hear a noise, especially a verbal noise, we set it in a context. We rehearse what we’ve heard, we anticipate what’s coming, and we ‘make up’ an extended present, as if we’d heard the whole sentence in one go. We can hold the entire sentence in our heads, as if we heard it as a sentence, and not one phoneme at a time.
    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 ‘kick-ass angel’ – bit of a generation gap there, which underlines how our perceptions are biased by our expectations. Ian recalls an Annie Lennox song that really went ‘a garden overgrown with trees’, but always sounded like ‘I’m getting overgrown with fleas’.
    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 thespatial 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 perceptions as your eyes move, and re-jig your invented image so that your new 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 cannot recognise tunes, not even ‘Happy Birthday To You’, and they have little or no sense of the difference between harmony and dissonance. There is nothing physically wrong with their hearing, however, and they were exposed to music as children. They are intelligent and have no history of mental illness. What seems to be wrong is that when it comes to music, they have no sense of an extended present. They cannot tap their feet in rhythm. They have no idea what a rhythm is. Their sense of timing is impaired. Mind you, so is their sense of pitch; they cannot distinguish sounds separated by an interval of two semitones – adjacent white keys on a piano. So the lack of an extended present is not the only problem. Congenital amusia is rare, and it affects males and females equally. Its sufferers have no difficulty with language, however, suggesting that the brain’s musicmodules, or at least those affected by amusia, differ from its language modules.
    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