Week 2: Lower-Level Vision Flashcards
1
Q
What are the different eye muscles?
A
- medial rectus
- lateral rectus
- superior rectus
- inferior rectus
- superior oblique
- inferior oblique
2
Q
What is the medial rectus‘ primary function?
A
Moves eye towards nose
3
Q
What is the lateral rectus‘ primary function?
A
Moves eye away from the nose
4
Q
What is the superior rectus‘ primary function?
A
Raises eye
5
Q
What is the inferior rectus‘ primary function?
A
Lowers eye
6
Q
What is the superior oblique‘s primary function?
A
Rotates eye
7
Q
What is the inferior oblique‘s primary function?
A
Rotates eye
8
Q
Which eye muscles counteract effects of which other eye muscles?
A
Superior oblique and inferior oblique counteract the rotational effects of superior and inferior rectus
9
Q
What is the Pupil
A
- Hole in the eye
- Controls intensity of light
-variable refraction
10
Q
What area of the eye transforms light into neural activity?
A
The fovea
(Fovea is a part of the retina)
11
Q
Where in the eye is the output?
A
The optic nerve
12
Q
Where do we have fixed refraction vs variable refraction in the eye?
A
- fixed: Cornea
- variable: Lens
13
Q
What is the point of central focus in the eye?
A
The fovea
14
Q
What is the Iris?
A
- the coloured area of the eye
- muscles controlling pupil dilation (→ light intensity)
15
Q
What are the different type of receptor cells in the retina?
A
Rods and Cones
16
Q
How many photoreceptor types are there in the retina?
A
4
→ three types of cones and rods
17
Q
What are the different types of cones in the retina?
A
- short - wave length cones (blue)
- medium-wavelength cones (green)
- short-wavelength cones (red)
→ the cone types do not uniquely specify colors → best to refer to them by their wavelength sensitivity profile
18
Q
What is the Purkinje shift?
A
- at lower light levels and with increasing dark adaptation peak
- luminance sensitivity sifts to the short wavelength end of the spectrum with low sensitivity for long wave length
- vision is taken over by rods → long wavelengths look darker
→ due to wavelength-dependent sensitivity between rods and cones
19
Q
What is rod vision?
A
Low sensitivity to long wavelengths
20
Q
Why do submarines use red light before surfacing?
A
- high rod sensitivity is required for perception at low light levels
- long wavelength light does not activate when too dark which bleaches the rods
- to release rods from bleaching, red light is turned on before surfacing
- during this red stage they are perceiving largely with m and l cones
21
Q
What are the different light levels?
A
Phototopic
Mesopic
Skotopic
22
Q
How do red and green appear at phototopic light levels?
A
Red appears brighter than green background
23
Q
How do red and green appear at skotopic light levels?
A
Red appears darker than green background
24
Q
Where is the blind spot in the eye?
A
- at the optic nerve (at around 15 degree angle)
- towards the temporal side (the ear side)
NOT 0 degree → that is where the fovea is
25
What is the optic nerve?
- the axons of the ganglion cells form a bundle: the point nerve
- transmits information to the central nervous system
26
How does the blind spot „work“?
- no visual input at blind spot region
- however, is NOT perceived as blank
- statistical properties of surrounding visual field regions are filled in (presumably at level of primary visual cortex)
27
What is the Receptive Field?
The (classical) receptive field of a visual neuron is the region of visual space where a suitable stimulus can directly cause and increase or decrease in spike rate
28
What is a suitable stimulus?
- stimulus might still need some additional properties to (de) activate the cell, a part from being in the right location
- e.g. in the V1 the stimulus needs to have a particular orientation
29
What is a non - classical receptive field?
- regions of visual space
- typically surrounding a classical receptive field
- a suitable stimulus cannot directly cause a change in spike rate, but it can modulate the effects of a suitable stimulus (=non-classical surround effects)
30
What is the density of cone types?
* fovea pit holds only cones
* periphery has mostly rods
31
What is the choroid?
- middle layer of the eye‘s outer wall
- between sclera and retina
32
What is the Sclera?
* white outer coating of the eye
* protection of the eyeball
33
What is the Aqueous Humour?
Clear liquid inside the front part of the eye
34
What is the vitreous Humor?
Liquid/ gel that fills area between Retina and Lens
35
What is the main visual pathway?
Retina
Optic nerves
Optic Chiasm
Lateral geniculate nucleus (LGN)
Early Visual Cortex (V1)
36
How many ganglion axions follow which visual pathway?
- 90% of ganglion axions follow main visual pathway
- other 10% go through superior colliculus
37
What is the Retina?
- part of the brain (develops from neural tube)
- the back surface of the eyeball
* projection of inverted image
- includes: photoreceptors, bipolar cells, amacrine cells, ganglion cells
38
Where is the information of which visual hemifield?
Left visual hemifield
- both eyes contain this information (nasal retina of left eye and temporal retina of right eye)
- reaches right LGN and V1
Right visual Hemifield
- both eyes contain this information (temporal retina of left eye and nasal retina of right eye)
- reaches left LGN and V1
39
What is the visual field?
The total area, expressed in degrees, of what can be seen with the eye when focusing on a central point
NOT = receptive field !!!
40
How big is the Human field of vision?
The binocular field is 120 degrees
41
What is the difference between the binocular and uniocular vision?
- binocular is the overlap of the visual fields from each eye
- uniocular if the visual field from a singular eye
- binocular vision allows for more detail, but has a smaller range
- depending on where the eyes are situated on the head, the differen fields are bigger or smaller
42
Where does the light hit the inside of the eye?
Retina
43
What is the optic chiasm?
Crossover of the nasal branches of the optic nerves
44
What is refraction?
= „bending“ of light, change of speed angle of light, when it passes from one medium to another (e.g. from air to water)
45
How does refraction take place in the eye?
- 80% of refraction in cornea
- 20% refraction in lens
- fixed in cornea
- variable in lens
46
Why do we have blurred vision when emerged in water?
- Water has same reflective index as cornea → eliminating cornea‘s focusing properties
- when in water, images are focused behind the retina → blurred image
47
How does the eye focus ?
- for distant focus the ciliary muscle is relaxed
- for close focus the ciliary msucle is contracted
48
What is visible light?
= an electromagnetic wave (=light) that can be perceived by the human eye
49
What are the different cells of the retina?
- photoreceptors
- bipolar cells
- amacrine cells
- horizontal cells
- ganglion cells
50
What is the difference between rods and cones?
- differ in sensitivity: rods are very sensitive („bleach“ easily), cones only activate at higher light levels (photopic/day vision
- rods allow to discriminate at low light levels (scotopic/night vision)
- cones allow to discriminate Color
51
What do the bipolar cells do?
Act as integrators of information
52
What do ganglion cells do?
Project their axons (through the Optic nerve) to the LGN (a part of the thalamus)
53
How does light turn into information?
1. light enters the eye and travels past optic fibres and ganglion/amacrine cells before hitting retina
2. photochemical reaction in rods and cones at the back of retina is triggered
3. chemical reaction activates bipolar cells → integration and centra-surround processing to enhance contrast
4. information is sent to visual cortex via thalamus
54
Why is the retina inverted?
The pigment epithelium absorbs light and increases sharpness
55
What is the consequence of an inverted retina?
The Blind Spot
56
What are photopigments?
- molecules that are sensitive to incoming lights
- they give the photoreceptors their corresponding wavelengths
57
What are the different types of photopigments?
- rhodopsin → rods
- photopsin (three different types) → cones
58
What is Phototransduction?
The process by which the absorbed light triggers an electrical signal in rods and cones
59
What is Chromatic Aberration?
- bending of the light on the lens depends on the wavelength of the light
- the lens optimises for the long (green and red) wavelengths
- blue light is defocused in front of retina
- green light is in focus on macula
- red light is defocused behind macula
- blue parts of image are always slightly blurred
- the reason why we have few short-wavelength cones
60
What are the different type of ganglion cells?
ON- Center and OFF-Center
61
How do the different ganglion cells react to light?
ON-Center
- if light is on the center: excitation during light period
OFF-Center
- if light in on the center: inhibition during light period
62
What is the Mexican hat model?
- model describing the receptive fields of retinal ganglion cells
- two functions: excitatory and inhibitory
- when added, we get inhibitory surround and excitatory center
- can model both on - and off-center receptive fields
- used in computer vision for edge detection
63
What is the Cornea?
* translucient layer in front of the eye/ lens
* fixed refraction
64
What is the fovea?
* center of the macula
* highest visual accuracy
* Color vision
65
What are the retinal layers form outer to inner?
* pigment epithelium
* photoreceptors
* horizontal cells
* bipolar cells
* amacrine cells
* ganglion cells
* nerve Fiber layer
66
What is contextual processing?
*horizontal and amacrine cells are responsible
* Center-surround processing
* integrate information horizontally across different locations
67
What is skotopic vision?
* only rods
* without daylight (night-vision)
* black and white
68
What is mesopic vision?
*rods and cones activated
69
What is photopic vision?
*only cones (rods bleached out)
* daylight (day-vision)
* colour vision
70
What does it mean, that our vision is active?
- eye muscles and movements help foveation
- direct our gaze without moving our head
- we can choose where we receive visual input
71
What are ciliary muscles?
Flatten or round out lens to allow for focus
72
What is lateral inhibition?
* inhibitory signals send from horizontal cells
* increases contrast and sharpeners in perception
73
What is a distal vs proximal stimulus?
Distal: the perceived physical object
Proximal: image that falls on the retina
74
What are graded potentials?
* Cause a change in the conductance of the Membrane of the sensory receptor cell
* primary generated by visual input
75
What is the difference between fovea, macula and retina?
The macula ist a part of the retina and the fovea (see fovea pit) is a part of the macula
