CHAPTER 4.2 READING GUIDE:
Name: ____________________________
The Visual System: Essentials of Sight
1. What is light? How does it travel? How do these vary (name AND describe)?
2. How does what most people call ‘light’ relate to the total range of wavelength? What must happen to this
light for us to be able to ‘see’?
Figure 4. 5
1. Wavelength relates to:____________
2. Amplitude relates to:_____________
3. Purity relates to: ______________
What types of rays on the range of
wavelengths are just shorter than the
visible spectrum? ________________
just longer? _____________________
3. What are the two main purposes of the eye?
4. What happens to light after it passes through the cornea and lens? Describe how the process of
accommodation relates to this.
5. For each of the following, describe the symptom, the reason for
the symptom, and how this occurs.
Nearsightedness:
Figure 4.7: List the correct order of the
following in which light passes
through/to: pupil, retina, lens, cornea
1.
2.
3.
4.
Farsightedness:
6. What controls the amount of light entering the eye by
controlling the size of the pupil? What’s the benefit when
the pupil is dilated? What’s the trade-off? When does this
occur and why?
Figure 4.9: View the image and read the text to
answer the questions below.
What begins once the rods and cones receive the
light and send out signals? ___________________
_________________________________________
What do the axons of ganglion cells form? ______
_________________________________________
7. What is surprising about the retina? How can the retina
be compared with the spinal cord?
What do you have where the optic nerve leaves the
eye (at the optic disk)? ______________________
8. For each of the following types of receptor cells in the retina, discuss A) the type of vision each specializes
in, B) how they respond to bright vs. dim light, C) their sensitivity to detail, and D) their location in relation to
the fovea.
Cones:
Rods:
9. What do both dark and light adaptation have in common in terms of visual acuity?
10. What do light striking rods and cones trigger? What does this do in turn? What does this carry? To where?
Figure 4.12
Where does input from the left half of the
visual field go? _______________________
Which hemisphere is it sent to? _________
11. Why do the optic nerves from the inside half of each
eye cross over at the optic chiasm?
What do the majority of nerve fibers pass
through after the optic chiasm (one word)?
______________________ From there they
go to the ____________________________
12. What are cells in the primary visual cortex actually sensitive to? Who found this out? What is the key point
of all this?
Figure 4.13
What does viewing a vertical line do to
the firing of a specific neuron cell in the
CAT’s visual cortex? ________________
A horizontal line? __________________
13. What happens to visual input after it’s processed in the visual
cortex? As the input moves further along the system, what can you say about neurons?
14. What is and what isn’t the probable explanation for cases of visual agnosia?
15. What do the findings of the study related to Greebies say about the functional organization of the brain?
16. How do the lights with the longest and shortest wavelengths appear in the visible spectrum? Why should
we take note of the word ‘appear’? If that is true, then what does our perception of color depend on?
17. How much light is left in relation to what was originally there for subtractive mixing? Additive mixing?
Figure 4.17
18. How does the trichromatic theory of color vision explain people’s
ability to see all the colors of the rainbow? Explain a practical
application of this theory.
What color do you get when you add
red, green and blue lights all together?
___________ What do you get when you
do the same for paint? _____________
19. Explain how the trichromatic theory also meshes with what is currently known about color blindness.
Elaborate on your first response by using the Reality Check box to explain why the misconception that
colorblind people see the world in black and white is wrong.
20. What is one argument against the trichromatic
theory? How does the color yellow fit in to another
argument against it?
Figure 4.18: If you stare at the color red
and then look at a blank piece of white
paper, what color will you see?
________________ If you look at green?
________________ What do you get if you
mix either of the above pairs? __________
21. What is main point of opponent process theory of color vision,
including two reason that lend validity to the theory?
Figure 4.19: Which theory of color
processing does the figure verify?
_________________________________
What is another way to describe the
wavelengths blue, green, and red cones
are receptive to? __________________
________________________________
22. Summarize how the two theories of color vision have been
reconciled.
23. Give two reasons why the color red is associated has a negative effect on performance in achievement
settings.