The Science of Discworld II

must be bouncing off. We naturally assume that the bat responds to echoes in the same kind of way that we would: it hears them. We naturally expect the qualia of bat echo-location to be similar to the human qualia evoked by sound-patterns, of which the richest example is music. So we imagine the bat flying along to the accompaniment of incredibly rapid rhythms played on bongo drums.
    However, this could be a false analogy. Echo-location is the main sense of a bat, so the ‘correct’ corresponding sense of a human is its main sense, which is sight, not hearing. The August 1993 edition of Nature has a picture of a bat on the cover, with the words ‘How bats’ ears see’. This refers to a technical article, by Steven Dear, James Simmons and Jonathan Fritz, who discovered that the neurons in the part of the bat’s brain that processes returning echoes are connected together in a very similar way to those in the human visual cortex. In terms of neural architecture, it looks very much as if the bat’s brain uses the echoes to build up an image of its surroundings. Analogously, today’s submarines use computers to turn a series of echoes into a three-dimensional map of the surrounding water. Figments of Reality developed this point to give a partial answer to Nagel’s question:
    [In effect] bats see with their ears, and their sonar qualia might well be like our visual ones. Intensity of sound might come over to the bat as a kind of ‘brightness’, and so on. Possibly the bat’s sonar qualia ‘see’ the world in black and white and shades of grey, but they could also pick up and render vivid various more subtle features of sound reflections. The closest analogy in humans is texture, which we sense by touch, but the bat could sense by sound. Soft objects reflect sound less well than hard ones, for instance. So bats may well ‘see’ textured sound. If so – and here our analogy is intended only as a very rough way to convey the idea – the sonar quale for a soft surface might ‘look’ green to the bat’s mind, that for hard ones might look red, that for liquid ones like a colour only bees can see, and so on …
    On Roundworld, such statements are no more than guesswork, supported by analogies of neural architecture. On Discworld, witches know what it feels like to be a bat, or a dog, or a beetle. And Angua the werewolf smells in colours, which is very close to our suggestion that bats hear in images and ‘see’ textures. But even on Discworld, the witches do not actually feel what it is like to be a bat. They feel what it is like to be a human who has ‘borrowed’ the sensory organs and neural processing equipment of a bat. It may feel quite different to be a bat when a witch is not hitching a free ride on its mind.
    Even though we can’t be certain what it feels like to be an animal, or another person, the attempt has several uses. As we said, the ability involved here is empathy: being able to understand what another person feels like. We’ve already seen that this is an important social skill, and that the same ability, deployed in a different way for a different purpose, gives us a chance to detect that someone else is lying to us. If we put ourselves inside their heads and realise that what they are saying is different from what we believe they are thinking, then we suspect them of lying.
    The word ‘lie’ has negative overtones, deservedly so, but what we’re talking about here can be constructive as well as destructive, and often is. For the purposes of the present discussion, a lie is anything contrary to the truth, but it’s not at all clear what ‘the truth’ is, or even whether there is only one of it, as the word ‘the’ would seem to indicate. When two people have a row, it is generally impossible for either of them, or anyone else, to figure out exactly what really happened. Our thoughts are tainted by perceptions. This is unavoidable, because what we think of as being ‘real’ is what our minds make of what comes from the sense organs: fudged, tuned, and mangled by a succession of interpretations by different bits of brain, plus some wallpaper additions. We never know what is really out there around us. All we know is what our minds construct from what our eyes, ears and fingers report.
    Not to put too fine a point on it, those perceptions are lies. The vivid