Chapter 5 (Module 5.1): Visual Coding

Question 1

What was Ibn al-Haytham’s evidence that we see only because light enters the eyes, not by sending out sight rays?

Answer 1

First, you can see distant objects such as stars far faster than we could imagine any sight rays reaching them.

Second, when light strikes an object, we
see only the light rays that reflect off the
object and into the eyes

Question 2

what does the law of specific nerve energies mean?

Answer 2

it states that the type of sensation experienced depends on the specific nerve fibers activated, not the nature of the stimulus

Question 2

If someone electrically stimulated the auditory receptors in your ear, what would you perceive?

Answer 2

Because of the law of specific nerve energies, you would perceive it as sound, not as shock. (Of course, a strong enough shock might spread far enough to excite pain receptors also.)

Question 2

If it were possible to flip your entire brain upside down, without breaking any of the connections to sense organs or muscles, what would happen to your perceptions of what you
see, hear, and so forth?

Answer 2

Your perceptions would not change The way visual or auditory information is coded
in the brain does not depend on the physical location within the brain.

Seeing something as “on top” or “to the left” depends on which neurons are active but does not depend on the physical location of those neurons.

Question 2

what is the fovea?

Answer 2

a tiny area specialized for acute, detailed vision

Question 2

what is the pupil?

Answer 2

an opening in the center of the iris

Question 2

what are the ganglion cells in the fovea of humans and other primates called?

Answer 2

midget ganglion cells

Question 3

what is the retina?

Answer 3

the rear surface of the eye

Question 3

What makes the blind spot of the retina blind?

Answer 3

The blind spot has no receptors because it is occupied by exiting axons and blood vessels

Question 3

what bipolar cells?

Answer 3

Bipolar cells are nerve cells (neurons) in the retina that play a crucial role in visual processing by connecting photoreceptors to ganglion cells

THE BRIDGE FOR INPUT FROM PHOTORECEPTORS TO GANGLION CELLS

Question 3

these cells refine the input to ganglion cells, enabling certain ones to respond mainly to particular shapes, directions of movement, changes in lighting, color, and other visual features

they also get the information from bipolar cells and send it to other bipolar, amacrine and ganglion cells

Answer 3

amacrine cells

Question 4

what are the two types of receptors contained in the retina?

Answer 4

rods and cones

Question 5

this type of receptor ion the retina are abundant in and near the fovea, less active in dim light

more useful in bright light

essential for color vision

Answer 5

Cones

Question 5

this type of receptor in the retina is abundant in the periphery of the human retina

responds to faint light but are not useful in
daylight because bright light bleaches them

Answer 5

rods

Question 6

this term refers to chemicals that release energy when struck by light

Answer 6

photopigments

Question 6

this type of proteins modify the photopigments’ sensitivity to different wavelengths of light

Answer 6

opsins

Question 7

what do photopigments consist of?

Answer 7

11-cis-retinal (a derivative of vitamin A)

Question 8

You sometimes find that you can see a faint star on a dark night better if you look slightly to the side of the star instead of straight at it. Why?

Answer 8

If you look slightly to the side, the light falls on an area of the retina with more rods and more convergence of input

Question 9

what is the trichromatic theory of color vision also known as?

Answer 9

Young-Helmholtz theory

Question 9

According to this theory, color perception begins with a given wavelength of light stimulating a distinctive ratio of responses by the three types of cones

Answer 9

trichromatic theory of color vision

Question 9

If you found a species with a high ratio of cones to rods in its retina, what would you predict about its way of life?

Answer 9

We should expect this species to be highly active during the day and seldom active at night

Question 9

what is the visual field?

Answer 9

the part of the world that you see

Question 10

According to this theory of color vision, visual system neurons beyond the receptors respond with an increase in activity to indicate one color
of light and a decrease to indicate the opposite color.

The three pairs of opposites are red-green, yellow-blue, and white-black

Answer 10

opponent-process theory

Question 10

Examine Figure 5.9. (GO TO DOCS)

According to the trichromatic theory, what causes you to perceive red?

Answer 10

Activity of the long-wavelength cone is not sufficient.

In fact, notice that the long-wavelength cone responds to what we call yellow more than to what we call red.

A perception of red occurs only if the long-wavelength cone has a high ratio of response relative to the other two types

Question 10

According to the opponent-process theory, under what circumstance would you perceive a white object as blue?

Answer 10

If you stared at a bright yellow object for a minute or so and then looked at a white object, it would appear blue

Question 10

this term refers to the ability to recognize colors despite changes in lighting

Answer 10

color constancy

Question 11

When a television set is off, its screen appears gray. When you watch a program, parts of the screen appear black, even though more light is actually showing on the screen than when the set was off. What accounts for the black perception?

Answer 11

The black experience arises by contrast with the brighter areas around it.

Question 11

this theory accounts for color and brightness constancy posits that the cortex compares information from various parts of the retina to determine the brightness and color for each area

Answer 11

retinex theory

Question 12

this term is also known as colorblindness

Answer 12

color vision deficiency

Question 13

Why is color vision deficiency a better term than color blindness?

Answer 13

Very few people see the world entirely in black and white. The more common condition is difficulty discriminating red from green