1. Seeing Things
Somewhere between a quarter and a third of humans’ neocortex is devoted to vision. We are very good at recognizing and distinguishing fairly subtle patterns, quickly decoding printed pages, for example, or distinguishing between trees based on the pattern of their leaves or bark. We accomplish this by having a very flexible and powerful visual system.

2. Understanding Sight Requires
Understanding Light
Understanding the Eye-Brain
Music to the deaf is like colour to the blind. How we see things depends on how our senses perceive things in the physical world and how our brain interprets what our senses perceive. In order to understand sight, we first have to understand what we call light in the physical world. We also have to understand how our eyes and brain work. This course will concentrate mostly on how light behaves in the physical world. The study of this is called Optics.

3. You may wish to delete these slides if you do not have this Hologram.
It’s wonderful how a hologram can be turned into an interest-generating button by gluing it onto any existing button. It is available at
Viewed from different angles, it demonstrates that understanding sight requires:
● understanding light (the Hologram itself)
● understanding the eye / brain (the different views of the Hologram)

4. Click to add notes.

5. (- are part of how we see.)
The Eye & Brain
(- are part of how we see.)
Open the applet MAESpiral.swf (included with permission in this folder) in a browser, if your internet connection is slow.
Or go to Instructions on how to adjust is in the Materials / Teacher Guide document.
Stand beside the projected image and have the class stare at the centre of the rotating spiral for about 20 seconds. Then have them look at your face. They will notice your head either growing larger or shrinking, depending on the direction of rotation. Don't worry, it won't last. The sensation will go away after a few seconds. It demonstrates that understanding sight requires understanding the brain. Then reverse the direction and repeat. Further explanations are on the bottom of the page.

6. Meet our “Eye-Brain”. We will use these often as observers on diagrams in this unit.
Eye-Brain graphics are by Patrick McWade > Used with permission

7. The tip of the candle flame emits light in all directions
The tip of the candle flame emits light in all directions. But we only see the light that enters our Eye-Brain.
Demonstrate that we can’t see the light that does not enter our eyes by using a laser pointer. Direct the laser beam across the classroom. Make the beam visible by misting water over the beam with a hand-held atomizer. As the tiny drops of water fall through the beam, they scatter light into the students’ eyes. This is called the Tyndall Effect. The Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds.

8. We don’t see light that does not enter our eyes.
Demonstrate that we can’t see the light that does not enter our eyes by using a laser pointer. Direct the laser beam across the classroom. Make the beam visible by misting water over the beam with a hand-held atomizer. As the tiny drops of water fall through the beam, they scatter light into the students’ eyes. This is called the Tyndall Effect. The Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds.

9. We don’t see light directed away from our eyes unless it is reflected into our Eye-Brain by something.
Demonstrate that we can’t see the light that does not enter our eyes by using a laser pointer. Direct the laser beam across the classroom. Make the beam visible by misting water over the beam with a hand-held atomizer. As the tiny drops of water fall through the beam, they scatter light into the students’ eyes. This is called the Tyndall Effect. The Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds.

10. On diagrams in this unit, we will tend to ignore all light that does not enter our Eye-Brains.
Demonstrate that we can’t see the light that does not enter our eyes by using a laser pointer. Direct the laser beam across the classroom. Make the beam visible by misting water over the beam with a hand-held atomizer. As the tiny drops of water fall through the beam, they scatter light into the students’ eyes. This is called the Tyndall Effect. The Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds.

11. The path light takes is called a Ray
The path light takes is called a Ray. Diagrams that show how light moves from the object to the eye are called Ray Diagrams.

12. Light is a type of energy our eyes are sensitive to
Light is a type of energy our eyes are sensitive to. This is called an Operational definition because it only tells us how we detect light but it does not tell us what light is.
Rectilinear Propagation

13. Can you see the Eye-Brain’s feet?
Rectilinear Propagation

14. Light travels in straight lines. This is called Rectilinear Propagation. Since no ray of light can go straight from the Eye-Brain’s feet into your eyes, you can’t see them.
Rectilinear Propagation
Experience has trained our Eye-Brain to expect that things are located in the direction that the light comes from.

15. Rectilinear Propagation

16. Newton was the first to note that white light breaks into the colours of a rainbow when it passes through a prism. These colours are called a Spectrum.
Sir Isaac Newton’s full name with title is easy to remember because of his initials (i.e. SIN).

17. When light from the Sun (White Light) is broken down, it’s Spectrum looks like this.
Very good full spectrum from overhead projector – Fisher Science Education - Diffraction Grating 6x5 Roll for overhead projector S Science First No.:PS-08-B
Encourage students to make up their own mnemonic for remembering the order of rainbow colours.
Let them know “A mnemonic is just a way to remember simple lists” .
To show students a very good full spectrum see
Note the Capital letters denote the Additive Primary colours. More on this later in “Seeing Colour.ppt”
Isaac Newton named the colours of the spectrum that we use today. At first, he only identified 5 colours (red, yellow, green, blue, violet). He changed this to seven colours out of a mistaken belief, derived from the ancient Greeks. They believed there was a connection between the colours, the musical notes, the known objects in the solar system, and the days of the week. Newton, therefore, added Orange and Indigo to make up 7 names for the main colours of the spectrum, i.e., ROYGBIV, Red, Orange, Yellow, Green, Blue, Indigo, Violet.
White Light is made up of shades of Red, Orange, Yellow, Green, Blue, and Violet. A mnemonic for remembering the order of rainbow colours is the name Roy G Biv.

18. When light from some sources is broken down, it’s Spectrum looks like a series of lines. All spectrum can be further separated until they appear as a series of lines.
Students will benefit by viewing various light sources, including Spectrum Tubes through Spectroscopes. This will clearly demonstrate most light is really made up of a series of pure colours.
The above Line Spectrum is from light coming from an iron heated until it gives off light. Most light sources are made up of many different colours.

19. Newton noted that the individual coloured lines could not be separated further. These lines are pure colours and are identified by a frequency and wavelength number.

20. A Conceptual definition gives a better understanding of what light is
A Conceptual definition gives a better understanding of what light is. The atoms in sources that produce light are surrounded by electrons that can be excited to higher energy levels.
As these electrons fall back to their original energy level, they give off the energy in the form of light.

21. There are many different ways for electrons to fall back
There are many different ways for electrons to fall back. Each jump backdown produces a different coloured line of light.
The Conceptual definition of light is; Light is produced when electrons change energy levels.

22. There are many ways for atoms to gain energy.
E3.1 describe and explain various types of light emissions (e.g., chemiluminescence, bioluminescence, incandescence, fluorescence, phosphorescence, triboluminescence; from an electric discharge or light-emitting diode [LED])
For instance, Incandescence is the emission of light from a body due to its temperature. The atoms gain energy by being heated.

23. Our ears cannot hear some high sound frequencies that dogs can
Our ears cannot hear some high sound frequencies that dogs can. Similarly, our eyes cannot “see” some of the colours of light.
Radiometer and hot iron
E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum

24. Some snakes can see Infra Red Radiation.
For instance, you cannot see if an iron is hot or not. Our eyes are not sensitive to the “colour” the iron emits but our hands can feel it. The “colour” hot irons emit is called Infra Red Radiation.
Some snakes can see Infra Red Radiation.
Radiometer and hot iron
E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum
The fact that some snakes can see Infra Red Radiation gives them the advantage of being able to better perceive warm blooded prey in the dark.

25. Similarly, you cannot see water heating in a microwave oven
Similarly, you cannot see water heating in a microwave oven. Our eyes are not sensitive to the “colour” the water can absorb. The “colour” that water is heated by is called Microwave Radiation.
Radiometer and hot iron
E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum

26. The Visible Light Spectrum is a very small part of a much larger spectrum called the Electromagnetic Spectrum.
E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum

27. Mnemonics for Remembering the Electromagnetic Spectrum
from Long to Short Wavelength
Radio Waves
Microwaves
Infra Red
Visible Spectrum
Ultra Violet
X-Rays
Gamma Rays
Raul's
Mother Is
Visiting
Uncle
Xavier's
Garden
Rabbits
Mate In
Very
Unusual
eXpensive
Gardens
Raging
Martians
Invade
Roy G. Biv.
Using
X-rays
& Gamma Rays
E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum
My Favourite from Short to Long Wavelength
Gamma Rays
X-Rays
Ultra Violet
Visible Spectrum
Infra Red
Microwaves
Radio Waves
Girls/Guys
eXperience
Unusual
Vibrations In My
Room

28. Visible Light can be produced from many energy sources
Visible Light can be produced from many energy sources. Astronomical objects, Bioluminescences, Triboluminescence, Chemoluminescence, Fluorescence, Phosphorescence, Incandescent, Combustion, and Light-emitting diode are types of Luminous sources .
E3.1 describe and explain various types of light emissions (e.g., chemiluminescence, bioluminescence, incandescence, fluorescence, phosphorescence, triboluminescence; from an electric discharge or light-emitting diode [LED])
A handout is supplied

29. Atoms in Luminous Objects emit light rays in all directions produced from other energy sources.

30. Atoms in Non-Luminous Objects scatter the light rays from Luminous Objects in all directions.

31. Atoms in all objects produce or scatter light rays
Atoms in all objects produce or scatter light rays. This diagram only shows light rays from atoms at the top and bottom of the objects.

32. To make diagrams simpler we only show one ray of light from the top and bottom of objects. Rays illuminating Non-Luminous objects are not shown.

33. To make things even simpler, we sometimes only show the rays coming from the top of the object. We always only show the light rays that enter the observer’s eye.

34. Rays of light travel from the object to the observer’s eye through a Medium. A Transparent Medium allows nearly all the rays to pass straight through unaltered. Air is a transparent medium.

35. An Opaque Medium absorbs or scatters all the rays
An Opaque Medium absorbs or scatters all the rays. A text book is an opaque medium.

36. A Translucent Medium transmits and scatters the rays
A Translucent Medium transmits and scatters the rays. The medium indicates whether it is being illuminated but the object cannot be clearly seen. Wax paper is a translucent medium.

37. On a ray diagram, the Object’s Location or Distance from the Eye-Brain is where all light rays appear to originate or come from.

38. To make the ray diagram simpler, we often only use one ray entering the eye. In this case, the Object’s Location or Distance from the Eye-Brain is where all rays originate if the eye changes position.

39. Try the Pencil Touch Activity
Two eyes in front of a head can determine the object’s location better because the rays entering each eye can be used by the Eye-Brain to triangulate where the object is. This is called Depth Perception.
Animals with eyes on the side of their heads can only see the object with one eye at a time. They cannot use the triangulation method to determine the object’s location. These animals must use the object’s apparent relative size to determine its location relative to other objects.
Pencil Touch Activity - Student activity to demonstrate Improved Depth Perception with two eyes.
Hold a pencil in both hands about arm’s length away but with BENT ELBOWS.
Close one eye and try to touch the points of the pencils together.
Repeat with both eyes open.
Discuss which is easier and why.
Try the Pencil Touch Activity

40. Floating Finger Procedure
The effect of two eyes on depth perception of the Eye-Brain is at the root of many visual curiosities. One of the oldest is called the Floating Finger.
Floating Finger Procedure
Hold your left and right forefingers about 30 cm in front of your eyes. Hold them horizontally about 2-3 cm apart.
Focus your eyes at a far point. Do not focus on your fingers.
Wiggle the fingers slightly up and down.
Try closing one eye at a time.
Explanation:
The eyes are focused on a far point; we still see objects that are closer to the eyes. The image from the left eye and the image projected in the right eye are both combined in our brain. This is the reason why we see only a piece of the overlap finger. Whatever image overlaps is seen more clearly. You would never be able to see the same floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, it is like looking at a picture where image depth can only be determined by the relative size.

41. Floating Finger
Did you see a piece of finger floating in the air?
Explanation:
The eyes are focused on a point located far away. The Eye-Brain uses two slightly different sets of rays to triangulate the distance.
But we still see objects that are closer to the eyes.

42. The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, image depth can only be determined by their relative size.
Left Eye Image
Explanation:
The eyes are focused on a far point, but we still see objects that are closer to the eyes. The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is more clear because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, it is like looking at a picture where image depth can only be determined by the relative size.

43. The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, image depth can only be determined by their relative size.
Right Eye Image
Explanation:
The eyes are focused on a far point, but we still see objects that are closer to the eyes. The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is more clear because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, it is like looking at a picture where image depth can only be determined by the relative size.

44. Images from Both Eyes combined in the brain
The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye image depth can only be determined by their relative size.
Images from Both Eyes combined in the brain
Explanation:
The eyes are focussed on a far point, but we still see objects that are closer to the eyes. The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlaps is more clear Because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye. It is like looking at a picture where image depth can only be determined by their relative size.

45. The effect of two eyes on depth perception of the Eye-Brain is also used in Magic Eye or Random Dot pictures.
See L1 Random Dot Demo (MS Word Document) plus Explanatory Demo in this folder.
You can demonstrate this with an overhead projector and two identical transparences of the Random dot diagram below. Hold the transparencies in clear “Presentation Sheet Protectors” in order to keep them properly aligned. You may have to trim them slightly to fit in the protectors. They should be able to slide smoothly.
Start by separating the transparences so that four fusion dots are projected.
Then slide them together. As the middle dots start to overlap you will see the “Hidden” circles moving toward the centre. Unfortunately, the overhead projector can only overlap and project one level at a time. It suggests the complexity of the brain which is able to overlap and view all the levels at once.
An estimated 5% of the population cannot see 3-D. This may be due to the following:
- poor coordination between the left and right eyes.
- eyeglasses with a HUGE difference in prescription for the left and the right eyes.
- Amblyopia (lazy eye) disorder characterized by poor or indistinct vision in an eye that is otherwise physically normal.
- Squint or Strabismus (eyes are not properly aligned) ~ 4% of the population.
People with one eye cannot see 3-D.

46. The apparent Size of the object depends on the angle between rays coming from the top and bottom of the object. Large objects have a large angle between the rays.

47. Objects that are farther away have a small angle between rays coming from the top and bottom. This makes them appear small to the Eye-Brain Objects that are close have a large angle between the rays, and the object appears larger.

48. If the Eye-Brain is confused about the location of the objects, then the object’s apparent size (dotted shapes) can be confused. The Eye-Brain may assume both objects are at the same distance. Then the distant object looks small compared to the close object.

49. Animals with eyes on the side of their heads can only see the object with one eye at a time. They cannot use the triangulation method to determine the object’s location. These animals must use the object’s apparent size to determine its location. Their depth perception will be poor.
Horse brain's have two halves that are not even connected. Trainers say, "be sure to do both sides of the horse” The left brain side does not communicate with his right side brain since they are not connected.

50. The Moon Illusion is an optical illusion in which the Moon appears larger when it is near the horizon than it does when it is higher up in the sky.
Text
Podcast

51. One of the possible explanations of the Moon Illusion is that the eye is confused about the location of the moon and surrounding objects. Therefore, the apparent size is confused.
Do Not measure this . It’s a bit of a lie