To further your child's understanding, you might compare the picture his brain gets from his senses to the way a television works. A television gets information from the air or from a cable, and the information is the same for every television set. But some sets have huge screens and some have small ones, some have color and some are black and white, some have high definition and some don't, some have stereo sound and some don't.

The picture on a television set may be too bright or too dark, have strange lines through it, or be beset by static. The sound may need to be adjusted. Maybe the remote doesn't work so well, and you really have to try hard to change the channels. Although the information coming from the outside is the same for each set, the picture that is delivered varies quite a bit, and that affects the viewing experience and impression of what's being watched.

That viewing experience can change, though. There are things the viewer can do to improve the situation. You learn where to aim the antenna. You fiddle with the settings long enough to find the optimum balance of brightness and color. You watch certain shows long enough that you can enjoy them and predict what's going on even if the picture's not perfect. You watch an episode so many times you can say the dialog along with the characters whether you can hear it well or not.

You know which shows make you feel happy, and you know which shows scare you so much you avoid that channel altogether. The picture itself is important, but it's never the whole story. What we add to it and how we adjust are important, too.

Keep in mind that children often learn better when they have a concrete example of what you're talking about. Try taking your child on a little field trip to an electronics store or department store, and go to the television department. Have him look at the huge variety of screens, all showing the same program, but with variations in size, color, clarity, reception, and special features. Although they should all be identical, it's hard to find any two that are really giving exactly the same picture.