NAME:

Psych 12

1.Complete the following experiment:

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2.Read the following information and answer the questions in your package:

We live in a3Dworld, and we perceive a 3D world. However, how we actually achieve3D visionis an intriguingpsychological question. After all, we only have a2D retina, so where does the extra dimension come from?

The most common answer to this question is to do with the fact thatwe have two eyes. Having twoeyes means we get two slightly different views of theworld. This can be seen by simply closing one eye after the other and switching views between them. You can see that objects in the world appear in different positions relative to each other. This is called “binocular disparity” and is the basis ofdepth perception.

If you notice, objects that are nearer to you seem to shift position in your visual more than those in thebackgrounddo. Thebraintakes the information from both eyes and combines it to interpret these disparities and give us a sense ofdepth. This method of perceiving 3-dimensions is known as “stereopsis” or “stereoscopic vision”.

Charles Wheatstonedemonstrated stereoscopic vision experimentally in the1800s, with his invention of thestereoscope, now often used atfun fairsand similar laces.Wheatstonetook twophotographs of the same scene usingcameras whoselenses were a fewcentimetres apart. This produced two pictures corresponding to theimages formed on theretinas of each eye.Wheatstone’s stereoscopeconsists of a peephole for each eye through which the pictures can be seen – the “left picture” through the left peephole, and the “right picture” through the right peephole. An observer will see a 3D image when looking through the stereoscope. This demonstrates that disparity produces a sense of depth.

However, people with only one functioning eye are still able to perceive a 3D world. Such people are obviously not using stereopsis. Also, not everyone develops stereoscopic vision. Children with asquint- orstrabismus– (a slight misalignment of the eyes) do not develop stereopsis unless their condition is corrected very early inlife, yet they can perceive depth too. There must be other ways to perceive in 3D than just stereopsis.

Hermann von Helmholtzproposed that we use a series of “cues and clues” to perceive the 3D world. The cues and clues he identified were:

  1. Occlusion:If anobjectis occluded, or covered, by another object in ourvisual field, then we infer that that object is behind the other.
  1. Shading/shadow:Theshadows objects cast on each other gives us an idea of their relative positions, given that we know where thelightsource is. This light source is theSun, so there are effects where we find that the brain automatically makes the assumption that the light source is coming from above.

For instance, if we look at pictures ofcraters on themoon, we see them as either craters or mounds depending on which way up we hold the picture. The confusion arises due to the fact that the pattern of shadow on a crater being lit from above is the same as mounds being lit from below. Since the brain assumes light is coming from above, we see mounds lit from below as craters lit from above, and craters lit from below as mounds lit from above.

  1. Geometric perspective:This relies on the simple principle thatparallel linesappear to converge as they go into the distance. This is a good method of perceiving depth so long as we live in a “carpentered” world, with its straight lines andright angles. There are someAfrican tribes, such as theZulutribe, that live in a world based aroundcirclesrather than right angles, and they do not have the ability to useperspectiveas a method of seeing depth.

1. Go to and follow the steps in the experiment.

2.Go to and watch the video until it is done.

3. Stare at the image below for 30 seconds. Then look at a blank piece of white paper. What do you see?

3. Read over the information about afterimages on the next pageand answer the questions in your package.

1.Complete the following experiment:

Eye Chart Vision Test

A Snellen eye chart is used to determine how "normal" your vision is. It sets a standard for what most people should be able to see when they stand 20 feet away from the chart. 20/20vision just means that when you stand 20 feet away from a Snellen eye chart, you see what a normal human being can see. If you see 20/40, that means that when you stand 20 feet away from the chart, you see what a person with "normal" visionsees when standing 40 feet away from it. The higher the second number, the worse your vision is. 20/200 (you see at 20 feet what a person with "normal" vision sees at 200) is the number for legal blindness in the United States.
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20/20 vision isn't perfect, it's just "normal." You can have better vision than 20/20. If you have 20/10 you see at 20 feet what most people see at 10. Some animals, like hawks, might have 20/2 vision!

You can use ourSnellen eye chart*to compare vision within your family or with your friends. (This will only give you an approximate idea of your vision. Your optometrist has much more precise tools to find out exactly how well you can see.) Each line of the chart is labeled on the left side. The second to last line is 20/20.

Stand twenty feet away from the chart and begin reading each line. Have a family member or friend watch to see that you are reading each letter correctly. The last line that you are able to read will give you an approximate idea of your vision. If you can read the very bottom line, your vision is 20/10! Now try covering one eye and just testing the other one. Is one eye better than the other?

2.Read the following and answer the questions in your package.

  1. Go to mrsvangelista.com and click on the link titled “Context is Everything”
  2. Complete the experiment that goes from p.1-3 that you find at the link
  3. Answer the question at the end of the package.

USE EXPLORER!

  1. Go to

and complete the experiment.

  1. Go to the website
  2. Answer the questions at the back of the package based on the website at #2.

Questions to Answer/30 marks

A)A 3D Leap of Faith. (12 marks)

  1. Which of your eyes is dominant?
  2. After reading the article, explain, in a short paragraph of about 150 words, the different ways we are able to see in 3D.

B) Oh My Tired Eyes(6 marks)

  1. How do our cone cells see colour?
  2. Explain how a cone can become “tired”. What happens when it does?
  3. How does the afterimage change in size? Why does it do this?
  4. Explain what happens to your eyes when you go into a dark area.

C)Going to the Eye Doctor(3 marks)

  1. Record your vision using the eye chart – what is the vision of each of your eyes.
  2. Explain how your brain’s mindset can trump your actual vision.

D)Context is Everything(2 marks)

  1. What do you learn about colour and vision from this experiment/reading?

E)Tricking Your Brain(5 marks)

  1. Which illusion did you like best and why?
  2. Explain how 4 of the different illusions work (not #4)

F)Learning to See(2 marks)

  1. Explain what you learn about learning!