5. Vision

Question 1

What happens when you see something?

a. You send out sight rays that strike the object.
b. Light rays reflect off the object and strike your retina.
c. You send out sight rays and light reflecting off the object strikes your retina.
d. You neither send out sight rays nor receive light rays onto your retina.

Answer 1

b. Light rays reflect off the object and strike your retina.

Question 2

If you look at a picture, how do the neurons in your brain represent it?

a. In a right-side-up pattern
b. In an upside-down pattern
c. Neither

Answer 2

c. Neither

Question 3

What is the law of specific nerve energies?

a. A stronger physical stimulus activates a larger number of sensory neurons.
b. Prolonged activation of a particular neuron weakens its response and leads to a different type of sensory experience.
c. The amplitude and velocity of an action potential determines which sensation it conveys, such as light or sound.
d. Each sensory neuron conveys a particular type of sensation, such as light or sound.

Answer 3

d. Each sensory neuron conveys a particular type of sensation, such as light or sound.

Question 4

What makes the blind spot of the retina blind?

a. It is at a location where the lens cannot focus the light.
b. It is usually damaged during the process of birth.
c. The optic nerve and blood vessels occupy this space, leaving no room for receptors.
d. It is in the shadow of the pupil.

Answer 4

c. The optic nerve and blood vessels occupy this space, leaving no room for receptors.

Question 5

Vision in the periphery of the retina has poor sensitivity to detail but great sensitivity to faint light. Why?

a. Toward the periphery, the retina has more midget ganglion cells.
b. Toward the periphery, the retina has more cones and fewer rods.
c. Toward the periphery, the retina has more convergence of input.
d. Toward the periphery, the light falls farther from the blind spot

Answer 5

c. Toward the periphery, the retina has more convergence of input.

Question 6

Input to the human visual cortex comes from cones and rods (by way of ganglion cells) in what proportion?

a. About 95 percent of input to the cortex comes from rods.
b. About 50 percent comes from rods and 50 percent from cones.
c. About 90 percent of input to the cortex comes from cones.

Answer 6

c. About 90 percent of input to the cortex comes from cones.

Question 7

Suppose you perceive something as red. According to the trichromatic theory, what is the explanation?

a. Light from the object has excited your long-wavelength cones more strongly than your other cones.
b. Light from the object has excited your short-wavelength cones more strongly than your other cones.
c. Ganglion cells that increase response to red and decrease their response to green are firing strongly.
d. Ganglion cells that increase their response to green and decrease their response to red are responding weakly.

Answer 7

a. Light from the object has excited your long-wavelength cones more strongly than your other cones.

Question 8

If you stare at a white circle surrounded by a green background, and then look at a white surface, you perceive a green circle surrounded by a red background. What does this observation imply about the opponent-process theory?

a. We perceive colors based on the pattern of input to the bipolar and ganglion cells of the retina.
b. The mechanisms of color vision vary from one species to another.
c. Opponent-process color perception depends on the visual cortex, not just the cells in the retina.
d. The opponent-process theory is wrong.

Answer 8

c. Opponent-process color perception depends on the visual cortex, not just the cells in the retina.

Question 9

An object that reflects all wavelengths equally ordinarily appears gray, but it may appear yellow, blue, or any other color, depending on what?

a. Brightness of the light
b. Contrast with surrounding objects
c. The culture in which someone grew up

Answer 9

b. Contrast with surrounding objects

Question 10

Which theory most readily accounts for the observation described in question 9?

a. Trichromatic theory
b. Opponent-process theory
c. Retinex theory

Answer 10

C. Retinex theory

Question 11

What evidence shows that color, such as greenness, is in the brain and not in the light itself?

a. Each wavelength excites a different set of cells in the retina.
b. Each wavelength excites a different set of cells in the visual cortex.
c. Increasing the intensity of the light changes the apparent color.
d. Some people are unable to see certain colors despite otherwise normal vision.

Answer 11

d. Some people are unable to see certain colors despite otherwise normal vision.

Question 12

What is the order of connections from receptors to visual cortex?

a. Receptors—bipolar cells—lateral geniculate—ganglion cells—visual cortex
b. Receptors—lateral geniculate—bipolar cells—ganglion cells—visual cortex
c. Receptors—ganglion cells—bipolar cells—lateral geniculate—visual cortex
d. Receptors—bipolar cells—ganglion cells—lateral geniculate—visual cortex

Answer 12

d. Receptors—bipolar cells—ganglion cells—lateral geniculate—visual cortex

Question 13

Axons from the nasal half of the retina go to the ___ hemisphere of the brain. Axons from the temporal half of the retina go to the ___ hemisphere of the brain.

a. contralateral . . . ipsilateral
b. contralateral . . . contralateral
c. ipsilateral . . . ipsilateral
d. ipsilateral . . . contralateral

Answer 13

a. contralateral . . . ipsilateral

Question 14

When light strikes a receptor, the effect is to ___ the bipolar cells and ___ the horizontal cells. The horizontal cells___ the bipolar cells.

a. excite . . . excite . . . excite
b. inhibit . . . inhibit . . . inhibit
c. excite . . . inhibit . . . excite
d. excite . . . inhibit . . . inhibit
e. excite . . . excite . . . inhibit

Answer 14

e. excite . . . excite . . . inhibit

Question 15

If light strikes one receptor, the net effect is to ___ the nearest bipolar cell and ___ other bipolar cells to the side because of the contributions from ___ cells.

a. excite . . . inhibit . . . other receptor
b. excite . . . inhibit . . . horizontal
c. excite . . . excite . . . other receptor
d. excite . . . excite . . . horizontal
e. inhibit . . . inhibit . . . horizontal

Answer 15

b. excite . . . inhibit . . . horizontal

Question 16

Suppose light strikes the retina in a circle, surrounded by dark. Which bipolar cells will show the greatest response, and which will show the least?

a. Bipolars connected to receptors in the center of the circle respond the most. Those connected to receptors farthest from the circle respond the least.
b. Bipolars connected to the receptors just outside the circumference of the circle respond most. Those connected to receptors just inside the circumference respond least.
c. Bipolars connected to the receptors just inside the circumference of the circle respond most. Those connected to receptors just outside the circumference respond least.

Answer 16

c. Bipolars connected to the receptors just inside the circumference of the circle respond most. Those connected to receptors just outside the circumference respond least.

Question 17

As we progress from bipolar cells to ganglion cells to later cells in the visual system, what happens to the size of receptive fields?

a. They become larger.
b. They become smaller.
c. They stay the same size.
d. They vary in size unpredictably.

Answer 17

a. They become larger.

Question 18

In contrast to parvocellular neurons, magnocellular neurons are more sensitive to ______.

a. color
b. small details
c. movement
d. the fovea

Answer 18

c. movement

Question 19

If you were in a darkened room and researchers wanted to know whether you were having visual fantasies (without asking you), they could measure activity in which brain area?

a. The retina
b. The lateral geniculate nucleus of the thalamus
c. The primary visual cortex
d. The parietal cortex

Answer 19

c. The primary visual cortex

Question 20

What is meant by blindsight?

a. Some people with damage to the primary visual cortex accurately guess the location or other properties of objects they say they don’t see.
b. Blind people learn to find their way around by making sounds and listening for echoes.
c. Blind people on average develop enhancements of hearing, touch, and other senses.
d. After damage to the eyes, other body parts become sensitive to light.
e. Incorrect hindsight.

Answer 20

a. Some people with damage to the primary visual cortex accurately guess the location or other properties of objects they say they don’t see.

Question 21

How could a researcher determine whether a given neuron in the visual cortex is simple or complex?

a. If it responds to a line or edge, it is a simple cell. If it responds only to more complex shapes, it is a complex cell.
b. If it responds to moving stimuli, it is a simple cell. If it responds to stationary objects, it is a complex cell.
c. If it responds to the same stimulus repeatedly, it is a simple cell. If it responds to a different stimulus each time it is tested, it is a complex cell.
d. If it responds to a stimulus in just one location, it is a simple cell. If it responds in several locations, it is a complex cell.

Answer 21

d. If it responds to a stimulus in just one location, it is a simple cell. If it responds in several locations, it is a complex cell.

Question 22

What do cells within a column of the visual cortex have in common?

a. They all have action potentials of the same amplitude and velocity.
b. They are all the same shape.
c. They are all simple cells, as opposed to complex cells.
d. They respond best to lines in the same orientation.

Answer 22

d. They respond best to lines in the same orientation.

Question 23

What is the evidence that certain types of feature detectors operate in the human visual cortex?

a. When you examine Mooney faces, at first you see only meaningless blobs, but with time and effort you start to perceive faces.
b. After you stare at a waterfall or other steadily moving display, you see stationary objects as moving in the opposite direction.
c. An electrode traveling through a section of the cortex may encounter one neuron after another with receptive fields in the same orientation.
d. Children who are deprived of input in one eye become attentive only to the other eye.

Answer 23

b. After you stare at a waterfall or other steadily moving display, you see stationary objects as moving in the opposite direction.

Question 24

If a kitten has one eye shut for its first few weeks of life, its visual cortex becomes insensitive to that eye. Why?

a. The receptors die.
b. Any axon that is not used for that long becomes unable to respond.
c. Activity from the active eye displaces synapses from the inactive eye.

Answer 24

c. Activity from the active eye displaces synapses from the inactive eye.

Question 25

What early experience is necessary to maintain binocular input to the neurons of the visual cortex?

a. Cortical cells will always maintain binocular responsiveness, regardless of their experience.
b. Cortical cells must receive some input to each eye every day.
c. Cortical cells must receive an equal amount of input from the two eyes.
d. Cortical cells must usually receive simultaneous input from the two eyes.

Answer 25

d. Cortical cells must usually receive simultaneous input from the two eyes.

Question 26

Why is it important to correct astigmatism early?

a. If uncorrected, the eyeball becomes even more asymmetrical over time.
b. Treatment is less expensive for children than for adults.
c. The visual cortex becomes more sensitive to the lines it sees best.
d. Uncorrected astigmatism can develop into cataracts.

Answer 26

c. The visual cortex becomes more sensitive to the lines it sees best.

Question 27

If someone is born with dense cataracts on both eyes, and the cataracts are removed years later, which of these aspects of vision remains permanently impaired?

a. Perception of the size of an object
b. Motion perception and depth perception
c. Ability to recognize whether two objects are the same or different
d. Perception of brightness and darkness

Answer 27

b. Motion perception and depth perception

Question 28

Within the visual system of the brain, the ventral stream is more important for ______ and the dorsal stream is more important for ______.

a. perceiving brightness . . . perceiving color
b. perceiving color . . . perceiving brightness
c. identifying objects . . . controlling movements
d. controlling movements . . . identifying objects

Answer 28

c. identifying objects . . . controlling movements

Question 29

Visual agnosia usually results from damage to which part of the cortex?

a. Occipital cortex
b. Temporal cortex
c. Parietal cortex
d. Frontal cortex

Answer 29

b. Temporal cortex

Question 30

What impairment is typical after damage to the fusiform gyrus?

a. Loss of color perception
b. Impaired perception of movement
c. Impaired ability to use vision in aiming arm and leg movements
d. Difficulty recognizing faces

Answer 30

d. Difficulty recognizing faces

Question 31

Which part of the visual cortex is most important for color vision, especially color constancy?

a. The fusiform gyrus
b. The dorsal stream
c. Area V4
d. Area MT

Answer 31

c. Area V4

Question 32

Why is it difficult to watch your own eyes move when looking in the mirror?

a. The eye movements are too fast to see.
b. The eye movements are too small to see.
c. During a saccadic eye movement, the eyes do not move relative to the background of the rest of the face.
d. During saccadic eye movements, activity decreases in area MT.

Answer 32

d. During saccadic eye movements, activity decreases in area MT.

Question 33

What happens after damage limited to area MT? What may occur if MT is intact but area V1 is damaged?

a. Damage to MT causes prosopagnosia. If MT is intact but V1 is damaged, the person can perceive faces but nothing else.
b. Damage to MT causes blindness. If MT is intact but V1 is damaged, the person suffers prosopagnosia.
c. Damage to MT causes motion blindness. If MT is intact but V1 is damaged, the person perceives movement but cannot identify the object.
d. Damage to MT causes blindness. If MT is intact but V1 is damaged, the person cannot perceive movement.

Answer 33

c. Damage to MT causes motion blindness. If MT is intact but V1 is damaged, the person perceives movement but cannot identify the object.

Tip- MT is Middle temporal Cortex - Important for lso known as area V5, and an adjacent region, area MST (medial superior temporal cortex) Areas MT and MST receive input mostly from the magnocellular path , which detects overall patterns, including movement over large areas of the visual field. Given that the magnocellular path is color insensitive, MT is also color insensitive.

Question 34

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

Answer 34

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 35

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

Answer 35

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 36

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 36

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 37

What makes the blind spot of the retina blind?

Answer 37

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

Question 38

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 38

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 39

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 39

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

Question 40

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

Answer 40

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

Question 41

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 41

The black experience arises by contrast with the other brighter areas. The contrast occurs by comparison within the cerebral cortex, as in the retinex theory of color vision.

Question 42

Figure 5.9 shows 500 nm light as blue and 550 nm light as yellow. Why should we nevertheless not call them “blue light” and “yellow light”?

Answer 42

Color perception depends not just on the wavelength of light from a given spot but also the light from surrounding areas. As in Figure 5.13, the context can change the color perception

Question 43

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

Answer 43

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

Question 44

Where does the optic nerve start and where does it end?

Answer 44

It starts with the ganglion cells in the retina. Most of its axons go to the lateral geniculate nucleus of the thalamus; some go to the hypothalamus and superior colliculus.

Question 45

When light strikes a receptor, does the receptor excite or inhibit the bipolar cells? What effect does it have on horizontal cells? What effect does the horizontal cell have on bipolar cells?

Answer 45

The receptor excites both the bipolar cells and the horizontal cell. The horizontal cell inhibits the same bipolar cell that was excited plus additional bipolar cells in the surround.

Question 46

If light strikes only one receptor, what is the net effect (excitatory or inhibitory) on the nearest bipolar cell that is directly connected to that receptor? What is the effect on bipolar cells to the sides? What causes that effect?

Answer 46

It produces more excitation than inhibition for the nearest bipolar cell. For surrounding bipolar cells, it produces only inhibition. The reason is that the receptor excites a horizontal cell, which inhibits all bipolar cells in the area.

Question 47

Examine Figure 5.17. You should see grayish diamonds at the crossroads among the black squares. Explain why.

Answer 47

In the parts of your retina that look at the long white arms, each neuron is inhibited by white input on two of its sides (either above and below or left and right). In the crossroads, each neuron is inhibited by input on all four sides. Therefore, the response in the crossroads is decreased compared to that in the arms.

Question 48

As we progress from bipolar cells to ganglion cells to later cells in the visual system, are receptive fields ordinarily larger, smaller, or the same size? Why?

Answer 48

They become larger because each cell’s receptive field is made by inputs converging at an earlier level.

Question 49

What are the differences between the magnocellular and parvocellular systems?

Answer 49

Neurons of the parvocellular system have small cell bodies with small receptive fields, are located mostly in and near the fovea, and are specialized for detailed and color vision. Neurons of the magnocellular system have large cell bodies with large receptive fields, are located in all parts of the retina, and are specialized for perception of large patterns and movement.

Question 50

If you were in a darkened room and researchers wanted to “read your mind” just enough to know whether you were having visual fantasies, what could they do?

Answer 50

Researchers could use fMRI, EEG, or other recording methods to see whether activity increased in your primary visual cortex.

Question 51

What is an example of an unconscious response to visual information?

Answer 51

In blindsight, someone can point toward an object or move the eyes toward the object, despite insisting that he or she sees nothing.

Question 52

How could a researcher determine whether a given neuron in the visual cortex is simple or complex?

Answer 52

First identify a stimulus, such as a horizontal line, that stimulates the cell. Then present the stimulus in several locations. If the cell responds strongly in only one location, it is a simple cell. If it responds in several locations, it is a complex cell.

Question 53

What do cells within a column of the visual cortex have in common?

Answer 53

They respond best to lines in the same orientation. Also, they are similar in their preference for one eye or the other, or both equally.

Question 54

What is a feature detector?

Answer 54

It is a neuron that detects the presence of a particular aspect of an object, such as a shape or a direction of movement.

Question 55

What is the effect of closing one eye early in life? What is the effect of closing both eyes?

Answer 55

If one eye is closed during early development, the cortex becomes unresponsive to it. If both eyes are closed, cortical cells remain somewhat responsive for several weeks and then gradually become sluggish and unselective in their responses.

Question 56

What early experience would cause a kitten or human child to lose stereoscopic depth perception?

Answer 56

If the eye muscles cannot keep both eyes focused in the same direction, the developing brain loses the ability for any neuron in the visual cortex to respond to input from both eyes. Instead, each neuron responds to one eye or the other. Stereoscopic depth perception requires cells that compare the input from the two eyes.

Question 57

What causes astigmatism?

Answer 57

Astigmatism results when the eyeball is not quite spherical. As a result, the person sees one direction of lines more clearly than the other.

Question 58

If an infant is born with dense cataracts on both eyes and they are surgically removed years later, how well does the child see at first?

Answer 58

The child sees well enough to identify whether two objects are the same or different, but the child doesn’t understand what the visual information means. In particular, the child cannot answer which visual display matches something the child touches. However, understanding of vision improves with practice.

Question 59

Suppose someone can describe an object in detail but stumbles and fumbles when trying to walk toward it and pick it up. Which is probably damaged, the dorsal path or the ventral path?

Answer 59

The inability to guide movement based on vision implies damage to the dorsal path.

Question 60

The brain has no specialized areas for perceiving flowers, clothes, or food. For what items does it have specialized areas?

Answer 60

The temporal cortex has specialized areas for perceiving places, faces, and bodies, including bodies in motion.

Question 61

The ability to recognize faces correlates with the strength of connections between which brain areas?

Answer 61

Ability to recognize faces correlates with the strength of connections between the occipital face area and the fusiform gyrus.

Question 62

Area V4 is important for color constancy. What is color constancy?

Answer 62

t is the ability to recognize the color of an object despite changes in the lighting.

Question 63

When you move your eyes, why does it not seem as if the world is moving?

Answer 63

Neurons in areas MT and MST respond strongly when an object moves relative to the background, and not when the object and background move in the same direction and speed.

Question 64

Under what circumstance does someone with an intact brain become motion blind, and what accounts for the motion blindness?

Answer 64

People become motion blind shortly before and during a saccade (voluntary eye movement), because of suppressed activity in area MT.