Math, Physics, and Babies
Math, Physics, and Babies
Anyone who has read even a little bit of psychology knows that the human mind is a strange thing. For example, we show marked and consistent psychological tendencies to think that, say, people with dilated pupils are more attractive, that people who smile a lot are untrustworthy, and that anything that has touched animal waste is disgusting. Where do we get these psychological dispositions? For hundreds of years, the prevailing view in psychology was that these beliefs resulted either from cultural influences that shaped our reasoning and information processing or simply from outright instruction (“Don't touch the dog poop, Johnny! You'll get sick!”).
But the prevailing view was wrong. We now have conclusive evidence that human minds come into the world with all sorts of “software” both preinstalled and booted up. Some of this software manifests itself right from birth, while other bits of it become operative at specifiable times in human development. For example, it has been shown that, from birth, human beings have certain beliefs about both mathematics and physics. Babies know, for example, that one plus one is not three, and they know that solid objects fall to the floor unless something or someone holds them up.
How do we know this? Like us, babies have certain ways of signaling their state of mind through their behavior. When you give babies the same sensory stimulus over and over, they (like us) tend to get bored with it and subsequently start to ignore it. When, on the other hand, you give them a series of novel, different, and unexpected sensory stimuli, they show their surprise by keeping their attention fixed on the unexpected event. Show them a picture of a red ball, and they will look. Flash it again, and they look again. Flash it a third, fourth, and fifth time, and in most cases their attention will start to drift, and they will start to attend to other things. This fact gives us a signal about babies' states of mind. When their attention remains fixed, it is obvious that what they are looking at is surprising or new to them. When their attention wanes, we can guess that what they are experiencing is old hat. Psychologists can thus infer some aspects of baby belief by measuring how long they fix their attention on certain things (that is, by measuring their “gaze time”).
How does this help us figure out babies' beliefs about math and physics? In one experiment researchers put babies on a table that had a screen that could be raised and lowered. When the screen is first put in place, the babies could see that there was nothing behind it. Experimenters would bring one object behind the screen from the left, and another from the right. Anyone who can think mathematically should then expect to find two objects behind the screen. And in fact, when the screen is dropped and there are two objects there, babies tend to look away quickly since that is just what they expected. That's boring! But when the screen drops and there is one object, or three objects, babies tend to gaze for a much longer time. In cases where one plus one does not seem to equal two, they are surprised. This shows us that babies know that one plus one equals two, not one or three.1
Another way we can look for beliefs that arise from built-in “software” is to look for beliefs that are pervasive across times and cultures. Widespread beliefs like that might sometimes be explainable simply in terms of experience. If we found that people across the globe uniformly believe that, say, all human beings have two feet, we could chalk that up as something learned through common human experience. But other pervasive beliefs seem to arise despite an absence of sufficient sensory evidence. Such beliefs are said to arise despite a “poverty of the stimulus,” and when such beliefs occur, we have reason to look for built-in, onboard processing mechanisms that provide what our experiences do not. A good example of this is the belief that rotting food, corpses, and animal waste are dangerous. This set of beliefs and the accompanying desires, known in psychology as “contagion avoidance,” is found across cultures, even in cases where people have little or no direct evidence for its truth. We are, it seems, just “wired” to believe it.2