Chapter 5 (Module 5.2) - How the Brain Processes Visual information

Question 1

what are the cells present within the eyeball?

Answer 1

1. Bipolar Cells
2. Amacrine Cells
3. Ganglion Cells
4. Horizontal Cells

Question 2

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

Answer 2

It starts with the ganglion cells in the retina.

Most of its axons go to the lateral geniculate nucleus of the thalamus, but some go to the hypothalamus and superior colliculus

Question 3

how does the retina sharpen contrasts to emphasize the borders of objects?

Answer 3

lateral inhibition

Question 4

this term refers to an area in visual space that excites or inhibits it

simply the point in space from which light strikes the cell

Answer 4

receptive field

Question 5

this term refers to the mechanism by which stimulation in any area of the retina suppresses the responses in neighboring areas, thereby enhancing the contrast at light–dark borders.

Answer 5

lateral inhibition

Question 6

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 6

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 7

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 7

It produces more excitation than inhibition surround 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 cell

Question 8

Examine Figure 5.17.

You should see grayish diamonds at the crossroads among the black squares.

Explain why

Answer 8

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 9

what are the three categories for primate ganglion cells?

Answer 9

1. Parvocellular Neurons
2. Magnocellular Neurons
3. Koniocellular Neurons

Question 9

this category of primate ganglion cells have small cell bodies and small receptive fields

located in or near the fovea

well suited to detect visual details

Answer 9

parvcoellular neurons

Question 10

this category of primate ganglion cells have large cell npdoes and receptive fields

are distributed evenly throughout the retina

respond strongly to movement and large overall patterns

Answer 10

magnocellular neurons

Question 11

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 11

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

Question 11

this category of primate ganglino cells have small cell bodies

but occur throughout the retina

responds to various stimuli

Answer 11

Koniocellular Neurons

Question 12

What are the differences between the parvocellular and magnocellular systems?

Answer 12

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 13

where does information from the lateral geniculate nucleus of the thalamus go?

Answer 13

primary visual cortex/area V1/ striate cortex

Question 14

this term refers o the ability to respond in limited ways to visual information without perceiving it consciously

Answer 14

blindsight

Question 15

what causes blindisight?

Answer 15

damage to the striate cortex

Question 15

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 15

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

Question 16

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

Answer 16

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

Question 17

this type of cell has a receptive field with fixed excitatory and inhibitory zones

Answer 17

simple cell

Question 18

this type of cell, located in areas V1 and V2 do not respond to the exact location of a stimulus

responds to a pattern of light in a particular orientation

Answer 18

complex cells

Question 19

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

Answer 19

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 19

this type of cell resemble complex cells with on exception: it has a strong inhibitory area at one end of its bar-shaped receptive field

Answer 19

End-stopped or hypercomplex cells

Question 20

what is the difference between a simple and complex cell?

Answer 20

a simple cell is a cell that responds to a stimulus in only one location while one that responds equally throughout a large area is a complex cell

Question 21

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

Answer 21

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 22

what are feature detectors?

Answer 22

neurons whose responses indicate the presence of a particular feature

Question 22

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

Answer 22

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 22

what is another name for lazy eye?

Answer 22

strabismus or strabismic ambylopia

Question 23

this term refers to the discrepancy between what the left and right eyes see

Answer 23

retinal disparity

Question 23

this term refers to the ability to perceive depth and three-dimensional space using visual information from both eyes

Answer 23

Stereoscopic Depth Perception

Question 23

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

Answer 23

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 24

this term refers to the blurring of vision for lines in one direction

Answer 24

astigmatism

Question 25

What causes astigmatism?

Answer 25

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 26

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 26

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 27

does each neuron in the visual system have a receptive field?

Answer 27

yes