Jacques Cousteau in Seashells
There's more to seeing than meets the eye.
Seeing is a cooperative effort involving your eyes and your brain. Your eyes may perceive a group of dots, but it is your brain that has to decide whether the dots form a pattern that means something. In the exhibit "Jacques Cousteau in Seashells," created for the Exploratorium by artist Ken Knowlton, a framed collection of seashells seems to be a random pattern when viewed up close. At a distance, however, the pattern is seen to be a likeness of well-known oceanographer Jacques Cousteau.

• Graph paper with 1/4 inch (6mm) squares.
• A black-and-white picture.
• A pencil.
• Paper clips.

(30 minutes or less)

You can use the pattern of dots supplied here for the To Do and Notice section, or you can make your own dot pattern. If you choose to make your own, you will need a black-and-white photograph of a simple, easily recognizable scene or person. (You could even use a picture of Jacques Cousteau!) You can translate this photo into a pattern of dots by following these steps:

1. Place graph paper on top of the photo. Paper clip the picture to the graph paper so it will stay in the same place while you are drawing.
2. Notice that dark portions of the photo show through the graph paper. Pick a square to start your drawing from. Estimate what portion of the square is black. Draw a dot whose size corresponds to the percentage of black you estimate is in the square - the more black in the square, the bigger your dot; see the diagram on the linked screen. If the square is not black but rather some shade of gray, the size of the dot will depend on how dark the gray is. In a square filled with pale gray, put a small dot; in a square filled with dark gray, put a bigger dot.
3. Repeat the process with each square in the picture until you are finished.

(5 minutes or more)

For simplicity, a picture of an eye is used in this Snack activity in place of the image of Jacques Cousteau.

Hold the dot picture at arm's length. If the dot picture is of a familiar object, it should be easily recognizable at this distance. See if other people can identify the object in the picture.

Unfamiliar or complicated objects may be more difficult to recognize at close range. Place the picture across the room, and you'll notice that it becomes much easier to recognize. The dots in the picture seem to disappear, and only the pattern remains. The picture may appear slightly fuzzy, but it certainly doesn't appear to be made of dots!

Pictures made of dots are easily recognized by the brain because the brain is always attempting to interpret what it sees. Even though the picture of the eye in this Snack is made up of different-sized dots, the brain recognizes the overall shape as that of an eye, since it is very familiar with that shape. This is the same reason a person may see shapes in clouds or inkblots. The brain does not merely register these shapes as abstract patterns, but attempts to interpret them based on previous experience.

The dots disappear when you view the picture from a distance because of the limited resolving power of your eyes. You see the dot picture because light reflecting from the page makes an image on the retina of your eye. This image stimulates the light-sensitive cells in the retina and your brain interprets the result. When you move the dot picture farther away from your eye, the image the picture makes on your retina becomes smaller. The images of the dots overlap on the light-sensitive cells. Unable to distinguish between adjacent dots, your eye perceives shades of gray, rather than black dots and white spaces.

To print shades of gray using black ink on white paper, printers use "halftone" reproduction. The phenomenon of the "disappearing" dots is the basis of these halftones. A magnifying glass will show you that printed photos in newspapers, books, and magazines are actually composed of thousands of tiny dots, often too small for the eye to separate.

Artists in the late nineteenth century, taking advantage of this phenomenon, created a style called Pointillism. Paintings in this style - most notably those by Georges Seurat (1859-91) - are made up of thousands of tiny dots of brilliant color that, at a distance, merge in the beholder's eye.

The picture on a color TV set is also made up of dots. Your eye blends these dots to make a picture.