How do we see

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Additional information

Useful websites

  1. Web interactives and additional information on Human Vision; Source: Olympus Microscopy Research
    This website has a lot of information on the structure of the eye, the mechanism of vision and eye problems.
  2. TED Video on "How do we see colour"

Reference Books

  1. NCERT Textbook Chapter Light
  2. NCERT Textbook Chapter Reflection and Refraction
  3. NCERT Textbook Chapter Human Eye and the Colourful World

Teaching Outlines

Concept #1 - The process of vision

Learning objectives

  1. We see because of the eye and the brain
  2. The eye has a lens, it processes images and the brain interprets
  3. There are colour and depth sensors in the brain

Notes for teachers

What is vision

  1. The human vision is a very complex process. Vision is a result of the two eyes working almost simultaneously with large portions of the brain to produce the sensation of vision.
  2. The first step in the process is the stimulation of the light sensitive receptors in the eye. This information of the image is then converted into electrical signals which are transmitted by the optic nerve to the brain where it undergoes a lot of pre-processing before reaching the visual cortices in the cerebrum. It is at the end of this process that we have a sense of vision.
  3. We must remember that the eye is actually an extension of the brain and is only one tool in the entire process of vision.
  4. Our eyes have one kind of light sensor that can make out the extent of brightness and 3 different kinds of colour sensors. These colour sensors are most sensitive to what we call the colours red, green and blue. For the other colours the three sensors will react differently. These colours are called primary additive colours because these colours are the ones to which our eye reacts most.
  5. We can receive a sensation of a particular colour either because light of that wavelength is shining into our eyes or because a mix of suitable primary colours is shining into our eyes. In either case we will see that colour. Different colours are produced by different mix of the three primary colours.

For more information click here.

Activity No #1 Our eyes can confuse us

  • Estimated Time - 20 minutes
  • Materials/ Resources needed - None.
  • Prerequisites/Instructions, if any - None. This is a set of two activities - not a full fledged experiment but a way of introducing the way our eyes can confuse us.
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)
  1. Ask the children to bring their index fingers together in front of their eyes at a distance of about 5-6 cm from the eyes. They should focus on a distant point in front of them and then move their fingers towards and away each other.
  2. They should be able to see a finger in the middle that seems to wiggle as they move the finger front and back or up and down!
  3. Get the children to look at an object first with one eye and then the other. They will see the image shift slightly – this is because the angle at which we see with each eye is slightly different.
  • Developmental Questions (What discussion questions)
  1. How is it that illusions are able to fool us? Why do we see an extra finger when we know there is no extra finger?
  2. We do not see only with our eyes –the eyes are only a part of the things that we need to see. We see because of our eyes, because of the nerves that connect our eyes to our brain and the brain itself.
  3. The brain makes sense of all the information that the eyes have given to it. Of course as we see in the case of the optical illusions the brain can be fooled sometimes. But most of the time it makes complete sense of what we see.
  4. Why do we have two eyes? They provide the brain with two different images which are separated by a small distance
  5. The two images go to the brain and the brain is able to get a 3D image of the object because of this.
  6. Remind them how we can fool the brain – we did that on the first day when we grew an extra floating finger!
  • Evaluation (Questions for assessment of the child)
  • Question Corner


Activity No #2 How do we see colours

  • Estimated Time - 50 minutes
  • Materials/ Resources needed - Computer, projector
  • Prerequisites/Instructions, if any - An introduction to nature of light, colour and wavelength
  • Multimedia resources
  • Website interactives/ links/ simulations

Colour-vision.png

  • Process (How to do the activity)
  1. Run the simulation - using one bulb at a time
  2. Have the students record what the man sees
  3. Discuss the following.
  • Developmental Questions (What discussion questions)
  1. When only one bulb is used, what colour does the man see? Why?
  2. When more than one colour is used, what colour does the man see? Why? Does this change if I move the sliders on each of the bulbs the man sees? If it changes, why does it change?
  3. When all the three bulbs are used, what is the colour that the man sees? Where else do we see white light? If R,G,B when mixed give the white light, what can you say about the nature of the red, green and blue.
  4. When does the man see any colour and when does he see black?
  5. What is the filter doing? Explain the difference in colour between the source being monochromatic (single colour) and white.
  • Evaluation (Questions for assessment of the child)
  • Question Corner

Concept #2 - The physiology of eye and vision

Learning objectives

  1. Eye is shaped like a ball – hence eyeball. Most of the ball is hidden inside but we can get a general feel when we put our eyes under our eye socket and gently feel it.
  2. The image is formed on the retina; the image is formed by the focussing action of the cornea and the lens.
  3. Introduction to vocabulary - Retina, Iris, Pupil, Cornea and Lens; the function of each in seeing.
  4. The lens shape is adjustable and this adjustable shape is what causes a sharp image to be formed on the retina – the lens adjusts its shape until a sharp image is formed in the lens.
  5. The retina is connected to the brain through the optic nerve. We can talk about the blind spot and the fovea.

Notes for teachers

The focus here is for the students to get a sense of the physiology of the eye - how big is it, how does the lens change shape and where the image is formed.


Activity No # 1 - The changing lens!

At the end of this experiment children should be able to recognize that changing the shape of a lens allows different kinds of images to form.Though no formal observations are needed, they must write what they did and what they saw in plain English.

  • Estimated Time- 50 minutes
  • Materials/ Resources needed
  1. Plastic bag
  2. Water
  3. Brightly coloured objects to view through the lens.
  • Prerequisites/Instructions, if any
  1. Introduction to lenses
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)
  1. Fill the plastic bag with water to about 2/3rds its capacity. It should be possible to squeeze it and change its shape without the water spilling out.
  2. Secure the Ziploc properly.
  3. Try looking through the Ziploc bag at various objects – including each other!
  4. Try moving the bag forward and backwards to see what the image looks like.
  5. Try squeezing the bag and see what happens to the image.
  6. Observations written in an organized format - aim of the experiment, method and questions below are to be answered in the observation
  • Developmental Questions (What discussion questions)
  1. What happened when we moved the bag backwards and forwards?
  2. What happened when we squeeze the bag and change its shape?
  • Evaluation (Questions for assessment of the child)
  1. Can you try and draw the ray diagram for this activity?
  • Question Corner


Activity No #2 - Accommodation in the eye

  • Estimated Time
  • Materials/ Resources needed
  • Prerequisites/Instructions, if any
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)
  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)
  • Question Corner

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