Lecture 5: Vision

Question 1

retina

Answer 1

layer of neurons in back of eye

Question 2

transduction

Answer 2

process of turning light into neural signals

Question 3

cornea

Answer 3

bends light entering the eye

Question 4

lens

Answer 4

changes shape to focus light on retina

Question 5

refraction

Answer 5

the bending of light rays

Question 6

ciliary muscles

Answer 6

adjust the focus by changing the shape of the lens

Question 7

the process of accommodation

Answer 7

contraction of the ciliary muscles causes nearer or farther images to come into focus

Question 8

eye movement is controlled by

Answer 8

three pairs of extraocular muscles

Question 9

farsightedness

Answer 9

as mammals age, their lenses become less elastic and therefore less able to bring nearby objects into focus

Question 10

nearsightedness

Answer 10

the most common vision problem in young people is myopia/nearsightedness, which is difficulty seeing distant objects

Question 11

normal vision

Answer 11

the cornea and lens refract light to focus a sharp image of the outside world on the retina

Question 12

myopia

Answer 12

eyeball is too long so images from distant objects are in focus in front of the retina. In this case, the image that reaches the retina is blurred

Question 13

myopia with correction

Answer 13

eyeglasses refract the light before it reaches the cornea to bring the images into sharp focus on the retina

Question 14

photoreceptors

Answer 14

sensory neurons in the retina that detect light:

rods - vision at low light levels
cones - colour vision

Question 15

bipolar cells

Answer 15

receive input from photoreceptors and synapses on ganglion cells, whose axons form the optic nerve, which carries information to the brain

Question 16

horizontal cells

Answer 16

in the retina contact photoreceptors and bipolar cells

Question 17

amacrine cells

Answer 17

contact bipolar and ganglion cells

Question 18

all cell types (in the retina) except ganglion cells generate:

Answer 18

only graded, local potentials, affecting each other through the graded release of neurotransmitters

Question 19

ganglion cells conduct

Answer 19

action potentials

Question 20

the humans eye contains about ___rods and______cones

Answer 20

100 million rods and 4 million cones, but only 1 million ganglion cells to transmit all that information to the brain

Question 21

scotopic system

Answer 21

rods; highly sensitive to dim light; low acuity; insensitive to colour; more numerous in the periphery, absent in fovea

Question 22

photopic system

Answer 22

cones; requires more light; sensitive to different wavelengths, enabling colour vision

Question 23

photoreceptors in dark continually release

Answer 23

neurotransmitter

Question 24

light triggers

Answer 24

hyperpolarization of the cell, causing it to release LESS neurotransmitter

Question 25

hyperpolarization is just as much as a signal as

Answer 25

depolarization is

Question 26

range refraction

Answer 26

uses different photoreceptors to handle different intensities

Question 27

photoreceptor adaptation

Answer 27

each photoreceptor adjusts its level of sensitivity to match the average ambient level of light

Question 28

visual acuity

Answer 28

a measure of how much detail we see and is sharpest in the center of the visual field

Question 29

fovea

Answer 29

center region of retina has a high density of smaller, tightly packed cones with high acuity this region receives direct light input that does not pass through other cells or blood vessels

Question 30

optic disc

Answer 30

where blood vessels and ganglion cell axons leave the eye

Question 31

blind spot

Answer 31

region on the retina that is sightless due to lack of photoreceptors in the optic disc brain system fill in missing information so that we perceive an uninterrupted system

Question 32

occipital cortex

Answer 32

ganglion cells conduct action potentials along axons that make up the optic nerve, which extends to the occipital cortex

Question 33

optic chiasm

Answer 33

some or all of each optic nerve crosses the midline at the optic chiasm after crossing, it is known as the optic tract in humans, axons from the medial retina (closer to your nose) cross to the opposite side of the brain axons from the lateral retina project to the same side of the brain

Question 34

Lateral geniculate nucleus

Answer 34

most axons of the optic tract terminate on the cells in the LGN of the thalamus

Question 35

Axons of the LGN neurons terminate in the:

Answer 35

primary visual cortex, aka the striate cortex of the occipital cortex

Question 36

visual cortical areas outside of V1 are called

Answer 36

the extrastriate cortex

Question 37

visual field

Answer 37

area that is visible without movement of the eye or head

Question 38

topographic projection

Answer 38

the retina represents a 2D map of the visual field this organization is perserved as the information travels through the brain as a topographic projection - much of the projection corresponds to the fovea, making high visual acuity possible

Question 39

receptive field

Answer 39

consists of the stimulus features that excite or inhibit the cell

Question 40

both rod and cone photoreceptors release the synaptic neurotransmitter:

Answer 40

glutamate light hyperpolarizes the photoreceptors causing them to release less glutamate

Question 41

on-center bipolar cells

Answer 41

turning on light in the center of its receptive field excites the cell because it receives less glutamate, which inhibits this type of bipolar cell

Question 42

off-center bipolar cells

Answer 42

turning off light in the center of the field excites the cells because they receive more glutamate and are depolarized

Question 43

on-center ganglion cells

Answer 43

on-center bipolar cells excite these cells when light is turned on

Question 44

off center ganglion cells

Answer 44

off-center bipolar cells excite these cells when light is turned off

Question 45

lateral inhibition

Answer 45

sensory receptor cells inhibit information from neighboring receptor cells, producing a contrast effect at the edges of regions

Question 46

Hubel and Wiesels theoretical model of visual analysis is:

Answer 46

Hierarchical: more complex receptor fields are built up from inputs of simpler ones

Question 47

simple cortical cells

Answer 47

also called bar detectors or edge detectors, respond to an edge or bar of a particular width, orientation, and location in the visual field

Question 48

complex cortical cells

Answer 48

respond best to a bar of a particular width and orientation that is in motion anywhere in the visual field

Question 49

spatial-frequency model

Answer 49

visual system analyzes the number of light-dark (or colour) cycles in any stimulus Some cycles are narrow, others broad. Some cycles of light-dark are oriented vertically, others horizontally, and others somewhere in between. If cortical neurons are indeed optimized to detect light-dark cycles, then they should respond to repeating bars of light, even better than to a single bar of light.

Question 50

From area V1, axons extend to other cortical areas involved in perception to form:

Answer 50

V2, V4, and the inferior temporal lobe.

Question 51

V2 is adjacent to

Answer 51

V1; responds to illusory boundaries and to complex relations among the parts of their receptive fields.

Question 52

V4 cells generally have a strong response to

Answer 52

frequency gratings. Some V4 cells produce strong responses to concentric, radial, or color stimuli. visual contrast

Question 53

Area V5 neurons respond to

Answer 53

moving stimuli. Woman with damage to V5: lost the ability to perceive motion

Question 54

Colour is perceived by the visual system as we detect differences in the

Answer 54

wavelength of photons within a certain range.

Question 55

Three dimensions of colour perception:

Answer 55

*Brightness–varies from dark to light *Hue–varies throughout all colors *Saturation–varies from full color to gray

Question 56

Trichromatic hypothesis of colour perception:

Answer 56

Three different types of cones (blue-sensitive, green-sensitive, and red-sensitive) *Each responds to a specific, different part of the spectrum *Each has a separate pathway to the brain *Color recognized based on which receptors are activated

Question 57

Opponent-process hypothesis of color perception:

Answer 57

*Four unique hues (blue, green, yellow, red) *Three opposed pairs of colors (blue versus yellow, green versus red, and black versus white) *Three physiological processes with opposed positive and negative values are the basis of color vision Neither of these old hypotheses are sufficient by themselves, but both are part of current colour-vision theory.

Question 58

Cones peak areas of wavelength sensitivity:

Answer 58

*Short (S)—420 nm *Medium (M)—530 nm *Long (L)—560 nm

Question 59

genes encoding photopigments are carried on the:

Answer 59

X chromosome—in those with female-typical chromosomes (XX) a normal copy can compensate for a defective gene. males are more likely to inherit this

Question 60

second stage of colour processing:

Answer 60

Most ganglion cells and LGN cells fire in response to some wavelengths and are inhibited by others. Spectrally opponent (color-opponent) cells have opposite firing responses to different regions of the spectrum. A plus L/minus M (+L/–M) cell is stimulated above 600 nm and inhibited at shorter wavelengths.

Question 61

Spectrally opponent ganglion cells:

Answer 61

Receive input from two or three different types of cones through bipolar cells Have excitatory connections from at least one input Have inhibitory connections from at least one input Record the difference in stimulation of different types of cones

Question 62

Spectrally opponent cells cannot be called color cells because

Answer 62

*They also send outputs to higher circuits for detection of form, depth, and motion *Their peak wavelength sensitivities do not correspond to the wavelengths we see as the principal hues

Question 63

Other spectrally opponent ganglion cells are stimulated or inhibited by

Answer 63

M and L cones and detect brightness or darkness.

Question 64

Two main processing streams originate in primary visual cortex:

Answer 64

Ventral stream: identifying objects (what) - - Damage causes problems in perceiving faces and objects. Dorsal stream: assessing the location of objects (where), and guiding our movement toward them - Opticataxia—difficulty using vision to reach for and grasp objects

Question 65

children who spend more time outdoors have a lower rate of:

Answer 65

myopia

Question 66

Misalignment of the eyes (lazy eye) can lead to

Answer 66

amblyopia— reduced visual acuity not caused by optical or retinal damage. *If eyes are not aligned properly during development, the primary visual cortex suppresses information from one eye, and this eye becomes functionally blind. *Eye muscles can be surgically adjusted to achieve better alignment. *If the weak eye is used regularly (cover the good eye), vision can be preserved in both eyes.