Chap 5 - Vision Flashcards Preview

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Flashcards in Chap 5 - Vision Deck (83)
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1

receptors of vision are sensitive to:

light

2

receptors ______ energy into electrochemical patterns so that the brain can perceive sights, sounds, smells.

"transduce" (convert)

3

Law of specific nerve energies

states that activity by a particular nerve always conveys the same type of information to the brain

Ex: impulses in one neuron indicate light; impulses in another neuron indicate sound

4

The eye to the brain

- light enters thru pupil
- light is focused by lens and cornea onto rear surface of eye (retina)
- visual receptors send msgs to neurons (bipolar cells)
- bipolar cells send msgs to ganglion cells
- axons of ganglion cells join (optic nerve)
- travels to the brain

5

Amacrine cells:

additional cells that receive info from bipolar cells and send it to other bipolar, ganglion, or amacrine cells

6

Amacrine cells fx:

control the ability of the ganglion cells to respond to shapes, movements, or other specific aspects of visual stimuli

7

optic nerve

consists of the axons of ganglion cells that band together and exit through the back of the eye and travel to the brain

8

The point at which the optic nerve leaves the back of the eye is called the ________ because it contains no receptors

blind spot

9

The central portion of the retina is the _______ and allows for acute and detailed vision

fovea

10

fovea

-Packed tight with receptors

- Nearly free of ganglion axons and blood vessels

11

Each receptor in the fovea attaches to a single bipolar cell and a single ganglion cell known as a :

midget ganglion cell

12

Each _____ in the fovea has a direct line to the brain which allows the registering of the exact location of input

cone

13

In the _________ of the retina, a greater number of receptors converge into ganglion and bipolar cells

periphery

- Detailed vision is less in peripheral vision

- Allows for the greater perception of much fainter light in peripheral vision

14

The arrangement of visual receptors in the eye is highly adaptive

Ex: predatory birds have a greater density of receptors on the top of the eye; rats have a greater density on the bottom of the eye

15

foveal vision

- receptors - cones

- convergence of input - each ganglion cell excited by a single cone

- brightness sensitivity - distinguishes among bright lights; responds poorly to dim light

- sensitivity to detail - good detail vision b/c each cone's own ganglion cell sends a message to the brain

- color vision - good (many cones)

16

peripheral vision

- receptors - portion of rods increase toward periphery

- convergence of input - each ganglion cell excited by many receptors

- brightness sensitivity - responds well to dim light; poor for distinguishing among bright lights

- sensitivity to detail - poor detail vision b/c many receptors coverage their input onto a given ganglion cell

- color vision - poor (few cones)

17

The vertebrate retina consists of two kinds of receptors:

- rods
- cones

18

rods

most abundant in the periphery of the eye and respond to faint light (120 million per retina)

19

cones

most abundant in and around the fovea (6 million per retina)

- Essential for color vision & more useful in bright light

20

Though cones are outnumbered, they provide about ______ of the brain’s input.

90%

21

The average number of axons in the optic nerve is ________, but some people may have two or three times as many

one million

22

Photopigments

chemicals contained by both rods and cones that release energy when struck by light

- Consist of 11-cis-retinal bound to proteins called opsins

- Light energy converts 11-cis-retinal quickly into all-trans-retinal

- Light is thus absorbed and energy is released that activates second messengers within the cell

23

color vision

- perception of color is dependent upon the wavelength of the light

- “Visible” wavelengths are dependent upon the species’ receptors

- shortest wavelength humans can perceive is 400 nanometers (violet)

- longest wavelength that humans can perceive is 700 nanometers (red)

24

Two major interpretations of color vision include the following:

- Trichromatic theory/Young-Helmholtz theory

- Opponent-process theory

25

Trichromatic theory/Young-Helmholtz theory

- color perception occurs through the relative rates of response by three kinds of cones
-Short wavelength, medium-wavelength, long-wavelength

-Each cone responds to a broad range of wavelengths, but some more than others
- The ratio of activity across the three types of cones determines the color
- More intense light increases the brightness of the color but does not change the ratio
- Incomplete theory of color vision
- Ex: negative color afterimage

26

opponent-process theory

- suggests we perceive color in terms of paired opposites

- brain has a mechanism that perceives color on a continuum from red to green and another from yellow to blue

- possible mechanism for the theory is that bipolar cells are excited by one set of wavelengths and inhibited by another

27

Both the opponent-process and trichromatic theory have limitations

- Color constancy
- Retinex theory

28

Color constancy

ability to recognize color despite changes in lighting, is not easily explained by these theories

29

Retinex theory

suggests the cortex compares information from various parts of the retina to determine the brightness and color for each area

- Better explains color and brightness constancy

30

Color vision deficiency

impairment in perceiving color differences

- Gene responsible is contained on the X chromosome (~8% of men &

31

Rods and cones of the retina make synaptic contact with ________ and ________.

- horizontal cells
- bipolar cells

32

Horizontal cells

cells in the eye that make inhibitory contact onto bipolar cells

33

Bipolar cells

make synapses onto amacrine cells and ganglion cells

34

ganglion cell axon form the ______

optic nerve

35

The ______ is the place where the two optic nerves leaving the eye meet.

optic chiasm

36

Most ganglion cell axons go to the ___________ , a smaller amount to the __________ , and fewer to other areas

- lateral geniculate nucleus
- superior colliculus

37

lateral geniculate nucleus

(neural basis of visual perception)

part of the thalamus specialized for visual perception

- Destination for most ganglion cell axons

- Sends axons to other parts of the thalamus and to the visual areas of the occipital cortex

- Cortex and thalamus feed information back and forth to each other

38

Lateral inhibition

(processing in the retina)

is the reduction of activity in one neuron by activity in neighboring neurons

- response of cells in the visual system depends upon the net result of excitatory and inhibitory messages it receives

- Lateral inhibition is the retina’s way responsible of sharpening contrasts to emphasize the borders of objects

39

receptive field

refers to the part of the visual field that either excites or inhibits a cell in the visual system of the brain

- For a receptor, the receptive field is the point in space from which light strikes it

- For other visual cells, receptive fields are derived from the visual field of cells that either excite or inhibit
(Ex: ganglion cells converge to form the receptive field of the next level of cells)

40

Ganglion cells of primates generally fall into three categories:

- Parvocellular neurons
- Magnocellular neurons
- Koniocellular neurons

41

Parvocellular neurons

- Mostly located in or near the fovea

- Have smaller cell bodies and small receptive fields

- Are highly sensitive to detect color and visual detail

42

Magnocellular neurons

- Are distributed evenly throughout the retina

- Have larger cell bodies and visual fields

- Are highly sensitive to large overall pattern and moving stimuli

43

Koniocellular neurons

- Have small cell bodies

- Are found throughout the retina

- Have several functions, and their axons terminate in many different places

44

Cells of the lateral geniculate have a receptive field similar to those of ganglion cells:

An excitatory or inhibitory central portion and a surrounding ring of the opposite effect

45

primary visual cortex (area V1)

receives information from the lateral geniculate nucleus and is the area responsible for the first stage of visual processing

46

Some people with damage to V1 show ______: an ability to respond to visual stimuli that they report not seeing

blindsight

47

Hubel and Weisel (1959, 1998) distinguished various types of cells in the visual cortex:

- simple cells
- complex cells
- end-stopped/hypercomplex cells

48

simple cells

- Fixed excitatory and inhibitory zones

- The more light that shines in the excitatory zone, the more the cell responds

- The more in the inhibitory zone, the less the cell responds

- Bar-shaped or edge-shaped receptive fields with vertical and horizontal orientations outnumbering diagonal ones

49

complex cells

-Located in either V1 or V2

- Have large receptive field that can not be mapped into fixed excitatory or inhibitory zones

- Responds to a pattern of light in a particular orientation and most strongly to a moving stimulus

50

end-stopped/hypercomplex cells

- Are similar to complex cells but with a strong inhibitory area at one end of its bar shaped receptive field

- Respond to a bar-shaped pattern of light anywhere in its large receptive field, provided the bar does not extend beyond a certain point

51

In the visual cortex, cells are grouped together in columns perpendicular to the surface

Cells within a given column process similar information

- Respond either mostly to the right or left eye, or respond to both eyes equally

- Do not consistently fire at the same time

52

Cells in the visual cortex may be ________ , neurons whose response indicate the presence of a particular feature/ stimuli

feature detectors

53

Prolonged exposure to a given visual feature ________ sensitivity to that feature

decreases

54

Animal studies have greatly contributed to the understanding of the development of vision

- Early lack of stimulation of ONE eye: leads to synapses in the visual cortex becoming gradually unresponsive to input from that eye

- Early lack of stimulation of BOTH eyes: cortical responses become sluggish but do not cause blindness

55

Sensitive/critical periods

are periods of time during the lifespan when experiences have a particularly strong and enduring effect

- Critical period ends with the onset of chemicals that inhibit axonal sprouting

- Changes that occur during critical period require both excitation and inhibition of some neurons

- Cortical plasticity is greatest in early life, but never ends

56

Stereoscopic depth perception

is a method of perceiving distance in which the brain compares slightly different inputs from the two eyes

- relies on retinal disparity

57

retinal disparity

or the discrepancy between what the left and the right eye sees

58

The ability of cortical neurons to adjust their connections to detect retinal disparity is shaped through _________.

experience

59

Strabismus

is a condition in which the eyes do not point in the same direction

- Usually develops in childhood
- Also known as “lazy eye”

60

If two eyes carry unrelated messages, cortical cell strengthens connections with only one eye

Development of stereoscopic depth perception is impaired

61

Early exposure to a limited array of patterns leads to nearly all of the visual cortex cells becoming responsive to ______.

only that pattern

62

Astigmatism

refers to a blurring of vision for lines in one direction caused by an asymmetric curvature of the eyes

- 70% of infants have astigmatism

63

Study of people born with cataracts but had them removed at age 7 or 12 indicate that vision can be restored gradually, but problems persist:

- Difficulty in recognizing objects

- Unable to tell that components are part of a whole

- Best prognosis is for children whose vision problems are corrected early in life

64

the "what" and "where" paths

- ventral stream
- dorsal stream

The two streams communicate
Each participates in identifying what and where an object is

65

secondary visual cortex (area V2)

receives information from area V1, processes information further, and sends it to other areas

Info is transferred between area V1 and V2 in a reciprocal nature

66

ventral stream

refers to the path that goes through temporal cortex; the “what” path

- Specialized for identifying and recognizing objects

67

dorsal stream

refers to the visual path in the parietal cortex; the “where” path

- Helps the motor system to find objects and move towards them

68

Damaging either stream will produce different deficits

- Ventral stream damage: can see where objects are but cannot identify them

- Dorsal stream damage: can identify objects but not know where they are

69

detailed analysis of shape

Receptive fields become larger and more specialized as visual information goes from simple cells to later areas of visual processing

70

inferior temporal cortex

contains cells that respond selectively to complex shapes but are insensitive to distinctions that are critical to other cells

- Cells in this cortex respond to identifiable objects

71

shape constancy

is the ability to recognize an object’s shape despite changes in direction or size

-The inferior temporal neuron’s ability to ignore changes in size and direction contributes to our capacity for shape constancy

- Damage to the pattern pathways of the cortex can lead to deficits in object recognition

72

Visual agnosia

is the inability to recognize objects despite satisfactory vision

- Caused by damage to the pattern pathway usually in the temporal cortex

73

face recognition

- occurs relatively soon after birth

- People w/ cataracts removed at 2-6 months develop nearly normal vision but have slight difficulties in distinguishing faces

- Newborns show strong preference for a right-side-up face and support idea of a built-in face recognition system

- Facial recognition continues to develop gradually into adolescence

74

Prosopagnosia

is the inability to recognize faces

- Occurs after damage to the fusiform gyrus of the inferior temporal cortex

- The fusiform gyrus responds much more strongly to faces than anything else

75

color preception

depends on both the light reflected on an object and how it compares with objects around it

- Area V4 may be responsible for color constancy and visual attention

- Color constancy

76

Color constancy

the ability to recognize something as being the same color despite changes in lighting

77

motion perception

involves a variety of brain areas in all four lobes of the cerebral cortex

78

middle-temporal cortex (MT/V5)

responds to a stimulus moving in a particular direction

79

Cells in the dorsal part of the ________________ respond to expansion, contraction or rotation of a visual stimulus

medial superior temporal cortex (MST)

80

MT and MST both receive input from the ________.

magnocellular path; color-insensitive

81

motion blindness

refers to the inability to determine the direction, speed and whether objects are moving

- Likely caused by damage in area MT

82

Some people are blind except for the ability to detect which direction something is moving

Area MT probably gets some visual input despite significant damage to area V1

83

Several mechanisms prevent confusion or blurring of images during eye movements

- Saccades - decrease in the activity of the visual cortex during quick eye movements

- Neural activity and blood flow decrease 75 ms before and during eye movements