Chapter 9: Vision

Question 1

What is a topographic map?

Answer 1

a spatially organized neural representation of the external world

Question 2

What do Muller cells do?

Answer 2

help transmit light through neurons to the photoreceptors

Question 3

What range of vision can humans see?

Answer 3

380nm-760nm

Question 4

What wavelengths/colours correspond with small, medium and large cones in most mammals? How do humans differ?

Answer 4

Blue: 419nm - Human: 426nm
Green: 531nm - Human: 530nm
Red: 559nm - Human: 552 or 557

Question 5

What type of light is below 400nm and what kind of animal can see it?

Answer 5

Ultraviolet light: butterflies and honeybees

Question 6

What type of light is above 700nm and what kind of animal can see it?

Answer 6

Infrared (night vision): snakes

Question 7

What is Myopia? What can it be caused by?

Answer 7

nearsightedness; a longer eyeball or curvature of the cornea; could be from too much strain (reading etc) or not enough bright light as a child (too much time indoors)

Question 8

What is Hyperopia? What is it caused by?

Answer 8

it is farsightedness; caused by a shorter eyeball or a lense that is too flat

Question 9

What is Presbyopia and what is it caused by?

Answer 9

oldsightedness; caused by the hardening of the lense so it can’t contract to view closer objects

Question 10

What are some properties of rods and what wavelength are they most sensitive to?

Answer 10

specialized for functioning at low light, more numerous, longer and cylindrical;for 496nm

Question 11

What are some properties of cones and what is the least common type of cone? What wavelength are they maximally responsive to?

Answer 11

specialized for colour and high visual acuity, responsive to bright light and fine detail; blue cones; 560nm

Question 12

What are the 6 types of cells in the retina?

Answer 12

1) Retinal ganglion cell
2) Amacrine cell
3) Bipolar cell
4) Horizontal cell
5) Cone
6) Rod

Question 13

What is a horizontal cell’s function?

Answer 13

to link the photoreceptors with bipolar cells

Question 14

What is an amacrine cell’s function?

Answer 14

to link bipolar cells with RGC

Question 15

What is a retinal ganglion cell? What are two categories of these cells?

Answer 15

a cell with axons that give rise to the optic nerve the transmit information from the photoreceptors to the brain; M cells and P cells

Question 16

What are characteristics of magnocellular cells? Where do they project to in the LGN and striate?

Answer 16

larger and receive information from rods; sensitive to moving stimulus; project to layers 1-2 in LGN and bottom part of striate

Question 17

What are characteristics of parvocellular cells? Where do they project to in the LGN and striate?

Answer 17

smaller and receive information from cones; sensitive to forms and colour; layers 3-6 in LGN and top part of striate

Question 18

Where does the Geniculostriate system pathway go? What type of axons are in this pathway?

Answer 18

retina –> lateral geniculate nucleus (in thalamus) –> layer IV of the visual cortex; all the P axons and some M axons; 90% of RGCs in here

Question 19

Where does the Tectopulvinar system pathway go? What type of axons are in this pathway?

Answer 19

retina –> superior collicus (in tectum) –> pulvinar (thalamus) –> parietal and temporal visual areas; the remaining M axons

Question 20

Where does the Retinohypothalamic tract go and what is it’s function? What cells form it?

Answer 20

it is formed by photo-retinal ganglion cells (pRGCs) which are RGC that absorb blue wavelength (460-480nm); it goes from the pRGCsto the suprachaismatic nucleus; it allows light to entrain the SCN’s rhythmic activity and contracts the pupil in response to light

Question 21

Where is the Dorsal Stream? What is it’s main function? What area of the visual cortex is crucial to it?

Answer 21

from area V1 to the parietal lobe; guides movements relative to objects; area V5

Question 22

Where is the Ventral Stream? What is it’s main function? What area of the visual cortex is crucial to it?

Answer 22

from area V1 to the temporal lobe; object identification and perceiving related movements; area V4

Question 23

What does ipsilateral mean? What layers in the thalamus do these neurons go to?

Answer 23

same side eye; layers 2, 3 & 5

Question 24

What does contralateral mean? What layers in the thalamus do these neurons go to?

Answer 24

opposite side eye; layers 1, 4 & 6

Question 25

Where do M cells go in the thalamus and where do they go in the visual cortex?

Answer 25

layers 1-2; IVC(alpha) in layer IV of cortex

Question 26

Where do P cells go in the thalamus and where do they go in the visual cortex?

Answer 26

layers 3-6; IVC(beta) in layer IV of cortex

Question 27

What is a corticol column and what is it's orientation and size?

Answer 27

it is anatomic organization that represents a functional unit; 6 corticol layers deep and 0.5mm(squared) in size; perpendicular to the surface

Question 28

Where is information sent from the medial and lateral pulvinar, respectively?

Answer 28

Medial: parietal lobe Lateral: temporal lobe

Question 29

What is a "blob" in area V1 and what does it do?

Answer 29

it is a region in area V1 that is revealed by staining cytochrome oxidase that contains colour sensitive neurons

Question 30

What are the 3 types of information Area V2 receives? How are they distinguished by staining?

Answer 30

1) Movement - thick stain 2) Colour - thin stain 3) Form - pale stain

Question 31

Where does information go after area V2?

Answer 31

to the other layers and then to area G in the parietal lobe and area E in the temporal lobe

Question 32

Where is the central vs periphery of the visual field located in the visual cortex? How do they differ in size?

Answer 32

Central: near the back and larger as a % of it's size Periphery: more anterior and smaller as a % of it's size

Question 33

What is on/off centre cell? What is a characteristic of them as a group?

Answer 33

a cell that has an excitatory or inhibitory centre and then the opposite surrounding it (circle shaped); they overlap a ton

Question 34

What is luminance contrast and what does it allow humans to do?

Answer 34

the amount of light an object reflects relative to its surroundings; it is how RGCs tell the brain about shape because it allows them to detect edges of shapes

Question 35

What is a simple cell? What does it do?

Answer 35

a cell with on/off rectangular receptive fields that detect orientation of specific bars of light in a particular direction

Question 36

What is a complex cell? What does it do?

Answer 36

a cell that is maximally excited by bars of light in a particular direction

Question 37

What is a hypercomplex cell and what does it do?

Answer 37

a cell that is maximally excited by moving bars and is usually strongly inhibitory at one end (helps to distinguish direction)

Question 38

How does the temporal cortex process shape? How are the neurons clustered in this area and why?

Answer 38

it responds to specialized things (faces, hands etc.); neurons with similar responsiveness to features cluster in columns - this helps with stimulus equivalence; these neurons are plastic

Question 39

What is subtractive mixing? What are the primary colours?

Answer 39

it is removing light from the mix (paint mixing); red, blue and yellow

Question 40

What is additive mixing? What are the primary colours?

Answer 40

increasing light to make colour; red, blue and green

Question 41

What is the Trichromatic theory of colour vison?

Answer 41

colour vision is based on the coding of 3 primary colours: red, green and blue from cones

Question 42

What is Protanopia?

Answer 42

a lack of red cones

Question 43

What is Deuteranopia?

Answer 43

a lack of green cones; dogs etc. can see through camo (army)

Question 44

What is Tritanopia?

Answer 44

a lack of blue cones

Question 45

What does area V1 respond to in regards to colour?

Answer 45

it responds to particular wavelengths or colours (red-green vs. blue-yellow)

Question 46

What does area V4 respond to in regards to colour? What may this be important for?

Answer 46

it responds to different PERCEIVED colours; important for colour constancy as lighting/backgrounds change

Question 47

What is Homonymous hemianopia and what does it result from?

Answer 47

blindness in left/right half of visual field; injury to the visual pathway leading to the cortex

Question 48

What is Quadratonopia and what does it result from?

Answer 48

blindness in part or "quadrant" of visual field; partial lesion to visual pathway leading to cortex

Question 49

What is Scotoma and what is it caused by?

Answer 49

a small blind spot caused by a migraine or small lesion

Question 50

What is Nystagmus and what does it prevent from being detected?

Answer 50

constant motion of the eye; Scotoma

Question 51

What does damage to the what (ventral) pathway lead to? What is an example of this happening?

Answer 51

it impairs distinguishing what things are, are like or are doing; D.F. in the shower with C.O. poisoning

Question 52

What is visual form agnosia? What is it a result of?

Answer 52

the inability to recognize objects or drawings of objects; damage to the ventral (what) pathway in the temporal lobe

Question 53

What does damage to the how (dorsal) pathway lead to? What is an example of this happening?

Answer 53

it leads to a deficit in guiding movements in relation to objects, like reaching to grab things; R.V. and his failure to pick up objects

Question 54

What is optic ataxia? What is it a result of?

Answer 54

deficit in visual control of reaching and other movements related to vision; damage to the dorsal (how) pathway in the parietal lobe

Question 55

What is rhodopsin and what process is it used in?

Answer 55

it is a pigment in rods that is extremely light sensitive and bleaches upon exposure to light; it takes 45min to regenerate (takes a while to see well in the dark)

Question 56

What is the Purkinje effect?

Answer 56

brightness of colours shifts; from yellow and red to blue at dusk because of a switch to usage of rods by the eyes

Question 57

What is the process by which rhodopsin bleaches and then allows for night vision?

Answer 57

light closes the Na+ channels which hyperpolarizes the cell and the rods transduce that there is light through inhibition; in the dark Na+ channels are opened and NT are released causing the rods to become extra sensitive to any light

Question 58

What is the association visual cortex and what is it's function?

Answer 58

it is outside the primary visual areas; usually it is more developed/complex and gives meaning to what is seen

Question 59

What is Prosopagnosia? What is damaged if this is present?

Answer 59

facial agnosia; the inferior prestriate cortex and adjoining portions of the inferotemporal cortex

Question 60

What is Akinetopsia? Where is damage typically for it? What types of activities does it cause difficulty for?

Answer 60

the inability to perceive fluid motion; V5 damage; pouring drinks and crossing the street