Technoteacher - Day 3

I Can’t See Straight!

Some robotic systems in space use visionics technology, which recognizes shapes in 3-D space. Here’s an exercise that shows why we need both our eyes to accurately determine where objects are.

• Place a pen in one hand and the cap in the other.
• Close one eye.
• Bend your arms slightly and try to put the cap on the pen.
• Can you tell if the cap is behind or in front of the pen?

Repeat with both eyes open. What happens? Each eye sends a different image to the brain. The brain then compares the images to judge the position of the objects for which it is receiving images. When you close one eye, the brain has trouble determining how far apart the objects are.

Topsy-turvy

To help students understand human vision and how it compares with an artificial vision system, make a classroom camera.

You will need:

	yogurt container
	black poster paint
	dishwashing liquid
	thumbtack
	an elastic
	tracing paper
	ruler
	a candle

Procedure

1. Paint the inside of the yogurt container with the poster paint. Add a drop of dishwashing liquid to help the paint stick to the container.
2. Once the paint has dried, carefully make a hole in the base of the container with the thumbtack (the hole will be the equivalent of the pupil of the eye).
3. Cover the other end of the container with tracing paper, which will serve as a screen (the paper will be the equivalent of the retina), holding it in place with the elastic. Your camera is ready.

Point the container at the lit candle, which should be placed about 50 cm away. The image on the screen will be upside down.

Explanation: the light from the candle passes through the hole and reaches the screen at the end of the container. Light beams travel in a straight line. When they go through the hole, the beams from the top of the flame are projected onto the bottom of the screen, while those coming from the base of the flame hit the top of the screen. The image is therefore inverted. The eye uses the brain to turn the image "right side up", while a camera does it via a reproduction process on paper or on a screen.

Observation: Bring a real camera into class and compare its functions with an illustrated cross-section of the human eye (opening and closing of the shutter/ iris, film/retina, etc.).

The Complexity of Vision

Vision is the most complex of the five senses. It uses more of the brain than all the other senses. Identify the parts of the human eye on an anatomical chart. Next, conduct experiments to show the various characteristics of vision.

Exercise A:

1. Use a light source to observe the iris opening and closing the pupil in a student’s eye to protect the sensitive cells of the inner eye.
2. On a card, draw a red square with side length 1 cm and a green circle of the same size, 5 cm apart.

Students should then take turns holding the card at arm’s length. Close the left eye and focus on the red square with the right eye. Slowly bring the card closer to the eyes. Does the green dot disappear? Close the right eye and repeat, focusing on the green dot. Point out that there is a spot in the back of the eye that doesn’t respond to light—it’s called the optic papilla, or blind spot. This is where the optic nerve, which sends images to the brain, meets the back of the retina (the eye’s screen). The circle or square disappears when it falls into the blind spot, because the optic papilla has no receptors (called cones or rods).

Exercise B:

1. On a card, draw two circles side by side, each 3 cm in diameter.
2. Colour the left circle dark blue and the right one light blue.
3. Have students take turns looking at the two circles.

Observation: the light-blue circle appears bigger. Light and bright colours seem to take up more space than dark colours. Have students do research on artificial vision, and compare the results of your observations with the characteristics of the human eye.