Perception

Vicky Greig

Have you ever thought about how you see things?

How do you know how big something is?

Why do you notice some objects and not others?

These are questions which psychologists have been studying for many years. They try to understand the way that people interpret what they see. For example, if you look out of your window perhaps you can see a tree on the horizon. Your eyes tell you that the tree is about one centimetre tall. But you know that is not true. Your knowledge about the world tells you that the tree is much bigger. Perhaps this seems simple but it is something we have to learn when we are children. If we didn't learn this we would find life very difficult.

Now let's look at an interesting example with colours. If you own a blue car, you know it is blue, even if it is in bright sunlight, in darkness or under a yellow street light. Your eyes tell you that it changes colour in these different situations, but your brain knows better. You have learnt that cars don't change colour all the time, and so your brain interprets the information your eyes give you.

Psychologists have found that people learn to understand and interpret what they see easily. One psychologist tried an experiment on himself. He put on a special pair of glasses. When he looked through them everything he looked at seemed to be upside-down. Try and imagine how that feels. At first, if he saw something on a high shelf, he bent down to pick it up because his eyes told him that the object was near the floor. But in a few weeks, he learnt to understand the strange, new world he saw. He lived normally without walking into things.

Sometimes, however, we make mistakes. Look at the Necker Cube below. Is the shaded part of the cube at the back or at the front?

Now look at it for a few minutes. Does the shaded part seem to move? This is an example of a visual illusion. The Necker Cube shows us that when we see an object, we make the best interpretation of it that we can. But sometimes we are wrong.

The way we see things is therefore more complicated than we imagine. Our eyes give us information all the time. But our brains decide what is important to us. For example, if you walk down a crowded street, you will see many faces. But you will probably not really notice them. But if you see someone you know, you will notice him immediately. From this example we can see that your brain chooses the visual information which is useful to you, and rejects the information which it does not need. The way your brain interprets that information depends on the knowledge you have about the world. And all this happens in less than a second.