Intuitive Physics, or, Everyone Loves a Balloon

christopherballoon1My son’s first birthday was yesterday. We bought a disposable helium tank and filled up a bunch of Curious George balloons. The picture included with this post is Christopher having the time of his life with those balloons.

I thought this would be a good jump off point for a discussion. I watch people and get curious and go look things up. A long time ago I noticed that my daughter would drop things from her high chair and then peer over the edge to the vast chasm of my kitchen floor, as if she expected them to fly back up to her. This, my friends, all relates to intuitive physics.

If you drop a bowling ball from an airplane, where will it hit the ground? If you said it would fall straight down, you, like me, fell for the intuitive, rudimentary notions your brain has about physics. In fact, the bowling ball will constantly be under the airplane because it was traveling at the same speed as the airplane and has not been acted on by any force to stop it. In essence, we all commit systematic errors when predicting the behavior of simple physical events.

How do we know that our brains have an innate, intuitive (yet often wrong) physics engine? Simple; we test babies.

To put it simply, we can test boredom in children. If a screen covers part of an image the child will pay attention for a period of time, and then look away. If the child only glances briefly at the image when the screen is removed, we can infer that there is not sufficient change in the image to interest the child and that the child must have known what was behind the screen. If the child stares at the image longer, we can infer that this is a new stimulus sufficient enough to engage the child.

Researchers bored children by showing them sticks poking out from behind the top and bottom of a screen. When two sticks moved in tandem, the infants saw them as a single object. When they did not move, the infants saw the two sticks as different objects.

Infants also seem to know that items cannot pass through one another, that items continue in fixed trajectories, that objects are cohesive (you cannot pick up part of the block), and that there is no action at a distance, that force moves objects. However, infants do not have such a firm grasp of gravity. They are surprised when something pushed off of a table hovers in midair, but they are not surprised when a dropped object stops falling before it hits the ground.

What does all of this tell us? It tells us that we have innate notions about the way the world works, and that those notions are hard to override in some situations. They’re not all correct, but they form a framework that we can use to understand the world from an early age.

Further Reading:

Kellman, P. J., & Spelke, E. S. (1983). Perception of partly occluded objects in infancy. Cognitive Psychology, 15, 483–524.

Pinker,S. (1997). How the Mind Works.New York: W.W. Norton & Company.

Spelke, E.S. (1990). Principles of object perception.

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