ingridscience

Print out the spot and cross image, or use the photo above.
Cover your right eye and hold the spot and cross image at arm’s length (or put your head at arms length from the computer screen), with your nose centred between the spot and the cross.
Stare at the cross, then slowly move the paper towards you/move your head towards the computer screen. Keep staring at the cross all the time; keep your nose centred; keep your eye covered.
When the paper /screen is 20-30cm away from your face, the spot disappears, as the spot is over the blind spot of your left eye.
This can be a tricky activity for some students - make sure you are staring at the cross the whole time.

The opposite can be done: cover your left eye, and stare at the circle while moving towards the image. The cross will disappear as it moves over the blind spot of your right eye.

We have a blind spot in each of our eyes where the optic nerve passes through the retina in the back of the eye. There are no light-sensitive cells in this area so it can not make images.

Hold the laser pointer up to the lens, and show how the light bends as it emerges from the lens.
The lens in our eye does the same thing, to project light from what we are looking at onto the back of our eye.

Use the lens to magnify newsprint or other small things.
(The lens in our eye can do the same thing).

Hold the lens in front of a white piece of paper to project an inverted view of a window or a bright light.
(The lens in our eye does the same thing).

Students look at their eye in the mirror.
Ask them to find their pupil. That is where the light comes in. It looks black because no light comes out again.
Find the iris, the coloured part. This is a muscle that opens and closes the pupil. What colour is your iris? What colour is your neighbour’s iris? Different people have different coloured iris muscles.
Students can find other parts of their eye e.g. eyelashes, sclera (white of the eye), eyelids.

Students can draw their eye.

We regulate how much light is coming into our eye by changing the size of the hole, the pupil.
Look at your eye in the mirror. Move the flashlight onto your pupil, then away, watching it.
Look for the pupil changing size. It should get smaller when the light shines on it, and larger when the light moves away.

Please note that in a class of students it is likely that one of them is at least partially colourblind (1 in 12 males are colourblind). As this is an activity distinguishing colours, these students will not be able to tell some colours apart and perceive some colours differently. The common red/green colour blindness means reds and greens (or colours containing reds and greens such as browns) look similar. More information at colourblindawareness.org and colorblindguide.com/post/the-advantage-of-being-colorblind.

Activity 1: Stare at the red and green cross for 20 seconds, then look at some blank white paper. Try not to blink after you move your gaze.

Activity 2: Stare at the black spot in the centre of the red circle for 20 seconds. Then slowly move the image away from your eyes, still staring at the black spot. You will see the inverse colour (light blue, or cyan) appearing as a halo around red circle.

The cells sensitive to a particular colour get tired when you stare at one colour for along time and stop sending signals to the brain. When you put white into the same field of view (either by moving your gaze, or by moving the image away from you), all the colour cells are now stimulated. The tired cells send a weak signal and the other cells send a strong signal, so you see the inverse colour from the original colour stared at.
(Staring at green makes green cells tires. Red and blue cells give a strong signal, perceived as magenta; inverse of red is blue and green giving cyan. Inverse of blue is red and green giving yellow).

Activity 3: Try making your own shapes from one or two bold colours. Use the method in activity 1 or 2 to play with colour perception.

About colourblindness:
About 1 in 12 men (8%) and 1 in 200 women in the world are colourblind, though not all the cases are extreme, and someone might not even realise they have partial colourblindness. Colour blindness is usually from a genetic cause (in your DNA and inherited from parents). The most common kind is red/green colourblindness, and is partial or complete loss of sensitivity to red and green colours. In the more extreme cases (protanopia - loss of red, and deuteranopia - loss of green) colours containing red or green appear yellow or brown, and blues and purples are confused. Less extreme cases (deuteranomaly - partial loss of green) are most common, where reds appear browner and purples appear bluer. https://en.wikipedia.org/wiki/Color_blindness#/media/File:Color_blindne…
Find out what it is like to be colour blind: http://www.colourblindawareness.org

Look at the foods that a black bear eats (see materials), and unnatural foods that they should not eat (human fast food).

Add bear food to a scale until there is enough for one black bear 'meal' (5kg). Compare with a person’s lunch (e.g. bagel and cheese)

Look at a bear skull to see the kinds of teeth they have to eat. Black bears are omnivores, eating plants and berries, as well as salmon and carrion meat. Their teeth are also used for defence.