The eye and retina Flashcards
1
Q
What is a distal stimulus?
A
A physical object in the environment
2
Q
Which cells carry out transduction?
A
Receptor cells
3
Q
Why is knowledge important in perception?
A
Top-down processing
Perception is a complex process
Knowledge can help simplify perception
4
Q
What is an absolute threshold?
A
The minimum quantity of something we can detect
5
Q
When we can perceive physical stimuli in the environment because of light, what is this known as in the perceptual process?
A
Distal stimulus
6
Q
Define light
A
Light is a form of electromagnetic energy
7
Q
A form of electromagnetic energy
A
Light
8
Q
Light varies in 2 physical dimensions. What are they?
A
1) Wavelength
2) Intensity
9
Q
Light varies in 2 psychological dimensions. What are they?
A
1) Colour
2) Brightness
10
Q
Does light wavelength relate to brightness or colour?
a. Brightness
b. Colour
A
b. Colour
11
Q
Does light intensity relate to brightness or colour?
a. Brightness
b. Colour
A
a. Brightness
12
Q
On the electromagnetic spectrum, what wavelength of light can we see with our human eye?
A
Visible spectrum
13
Q
True or False?
Light is absorbed from objects and into the eye
A
False
Light is reflected from objects and into the eye
14
Q
When we can perceive physical stimuli after light reflects from objects and into the eye, what is this known as in the perceptual process?
A
Proximal stimulus
15
Q
What is located inside the retina that allows for transduction?
A
Receptors
16
Q
True or False?
Receptors are located in the retina
A
True
17
Q
What is the function of the eye?
A
The function of the eye is to focus the image on the retina
18
Q
What is the iris?
A
The coloured part of the eye (brown, blue, green)
19
Q
What is the pupil?
A
The black circle inside the iris
20
Q
The coloured part of the eye (brown, blue, green)
What is this?
A
The iris
21
Q
What are the 3 main purposes of the iris and pupil?
A
1) Adjustable aperture
2) Limit the amount of light passing through
3) Allows us to deal with a great range of light levels
22
Q
How wide is the pupil?
A
Pupil is between 2 mm and 9 mm in diameter
23
Q
What is the shared role between the cornea and lens?
A
The role is to focus light on the retina
24
Q
The role is to focus light on the retina
What part(s) of the eye is responsible for this role?
A
Cornea and Lens
25
1) Adjustable aperture
2) Limit the amount of light passing through
3) Allows us to deal with a great range of light levels
What part(s) of the eye is responsible for this role?
Iris and Pupil
26
The outer surface of the eye, which is transparent, is called...?
Cornea
27
The cornea has ........% focusing power
80%
28
The lens has ....% focusing power
20%
29
Has 80% focusing power
What part(s) of the eye is responsible for this role?
Cornea
30
What part(s) of the eye is responsible for this role?
Shaped like a dome and bends light to help the eye focus
Cornea
31
Some of the light enters the eye through an opening called the ......?
Pupil
32
What part(s) of the eye is responsible for this role?
Controls how much light the pupil lets in
Iris
33
What part(s) of the eye is responsible for this role?
Changes in shape due to the action of ciliary muscles
Lens
34
What allows the lens to change its shape?
The contraction or relaxation of the ciliary muscles
35
Why do lenses change shape?
To focus on objects at various distances (changes the amount of focusing power)
36
As the distance of an object varies, what is the name of the process where the eye changes the focal length of the lens by changing the curvature of the lens?
Accommodation
37
Define accommodation
As the distance of an object varies, the eye changes the focal length of the lens by changing the curvature of the lens
38
When the eye focuses on closer objects, does the lens...?
a. Become fatter
b. Become thinner
a. Become fatter
39
When the eye focuses on far objects, does the lens...?
a. Become fatter
b. Become thinner
b. Become thinner
40
Why does the lens become fatter when attempting to focus on near objects?
To allow the light rays to refract (bend) more strongly
41
Why does the lens become thinner when attempting to focus on far objects?
To allow the light rays to refract (bend) only a little bit/slightly
42
What are the 2 types of refractive errors?
1) Myopia
2) Hyperopia
43
What is Myopia in simple terms?
Nearsightedness
44
What is hyperopia in simple terms?
Farsightedness
45
What results in myopia?
- The eye focuses light in front of your retina instead of onto it
- The retina is the surface at the back of your eye that collects light and changes the light into electrical impulses that your brain reads as images
- When the eye focuses light in front of the retina, it can result in blurred vision for far away objects
- It is likely that the eyeball is a little too long (oval-shaped rather than round) or the cornea is too rounded = light rays bend too much
46
What results in hyperopia?
- The eye focuses light behind your retina instead of onto it
- The retina is the surface at the back of your eye that collects light and changes the light into electrical impulses that your brain reads as images
- When the eye focuses light behind the retina, it can result in blurred vision for near objects
- It is likely that the eyeball is a little too short than normal and the cornea is overly flattened = light rays bend too little
47
People with myopia must wear what type of lens for their glasses?
Concave lens
48
People with hyperopia must wear what type of lens for their glasses?
Convex lens
49
How do concave lenses correct myopia?
Allows the light entering the lens to diverge so that it will correctly focus on the retina
The concave lens pushes the rays of light further apart so that they arrive together in proper focus at the back of the eye
50
How do convex lenses correct hyperopia?
Allows the light entering the lens to converge so that it will correctly focus on the retina
The convex lens brings the rays of light closer together so that they arrive together in proper focus at the back of the eye
51
Which lens is thicker in the middle?
a. Concave
b. Convex
b. Convex
52
Which lens is thinner in the middle?
a. Concave
b. Convex
a. Concave
53
Light- (photo-) sensitive layer at the back of the eye
This is known as...?
The retina
54
Define the retina
Light- (photo-) sensitive layer at the back of the eye
55
What are the 6 different types of cells in the retina?
1) Optic nerve
2) Retinal ganglion cells
3) Amacrine cells
4) Bipolar cells
5) Horizontal cells
6) Photoreceptors
56
What part of the eye contains:
1) Optic nerve
2) Retinal ganglion cells
3) Amacrine cells
4) Bipolar cells
5) Horizontal cells
6) Photoreceptors
Retina
57
Light-sensitive cells are known as...?
Photoreceptors
58
What cells turn light into electrical impulses?
Photoreceptors
59
Photoreceptors turn light into electrical impulses. What is the name of this process?
Transduction
60
Define Transduction
When photoreceptors turn light into electrical impulses
61
What cells carry out transduction?
Photoreceptors
62
Define photoreceptors
Light sensitive cells
63
How does transduction occur?
Visual photopigments react to light and trigger electrical signals
64
What are the 2 types of photoreceptors?
1) Rods
2) Cones
65
Which is longer?
a. Rods
b. Cones
a. Rods
66
Which has a head that has a similar shape to a leaf?
a. Rods
b. Cones
b. Cones
67
Which has a head that has a similar shape to a comb (rectangle head)?
a. Rods
b. Cones
a. Rods
68
Which is shorter?
a. Rods
b. Cones
b. Cones
69
Which has more in the retina?
a. Rods
b. Cones
a. Rods
70
Which has less in the retina?
a. Rods
b. Cones
b. Cones
71
How many rods are there in the retina?
120 million in each retina
72
How many cones are there in the retina?
6 million in each retina
73
Rodes and Cones differ in terms of...? List 5 differences
- Number
- Sensitivity
- Involvement in colour perception
- Retinal distribution
- Neural convergence & acuity
74
Which photoreceptor is more sensitive?
a. Rods
b. Cones
a. Rods
75
Which photoreceptor works really well in dim light and at night?
a. Rods
b. Cones
a. Rods
76
Which photoreceptor is more useful in daylight?
a. Rods
b. Cones
b. Cones
77
Which photoreceptor is less sensitive?
a. Rods
b. Cones
b. Cones
78
Which photoreceptor is better at picking up low levels of light?
a. Rods
b. Cones
a. Rods
79
Which photoreceptor is useless at night?
a. Rods
b. Cones
b. Cones
80
Which photoreceptor is useless in daylight?
a. Rods
b. Cones
a. Rods
81
What is scotopic vision regime/sensitivity?
When only rods are active in the retina
82
What is photopic vision regime/sensitivity?
When only cones are active in the retina
83
What is mesopic vision regime/sensitivity?
When both rods and cones are active in the retina
84
When only cones are active in the retina
Is this...?
a. Scotopic
b. Photopic
c. Mesopic
b. Photopic
85
When both rods and cones are active in the retina
Is this...?
a. Scotopic
b. Photopic
c. Mesopic
c. Mesopic
86
When only rods are active in the retina
Is this...?
a. Scotopic
b. Photopic
c. Mesopic
a. Scotopic
87
Where there's no moon or sun (dim/dark light) outside.
What vision regime is used?
a. Scotopic
b. Photopic
c. Mesopic
a. Scotopic (only rods are active)
88
Where there's moonlight or early twilight (some light) outside.
What vision regime is used?
a. Scotopic
b. Photopic
c. Mesopic
c. Mesopic (both rods and cones are active)
89
Where there's full sunlight (a lot of light) outside.
What vision regime is used?
a. Scotopic
b. Photopic
c. Mesopic
b. Photopic
90
When do photoreceptors stop responding?
When there is bright light
Bright light bleaches photopigments so photoreceptors stop responding
91
An increase in the eye's sensitivity in the dark is known as...?
Dark adaptation
92
Define dark adaptation
An increase in the eye's sensitivity in the dark
93
Going from bright to dark allows photoreceptors to do what?
To "recover" or regain sensitivity after having their photopigments bleached from bright light
94
The process whereby the retina adapts to decreasing levels of illumination is...?
Dark adaptation
95
Which process entails a transition from a cone to a rod activity, and thus a change in light sensitivity?
Dark adaptation
96
After 20-30 minutes in the dark, sensitivity is about (...........) times greater than the sensitivity in light
100,000
97
Transitioning from being in the light from outside and coming into a dark room, do cones adapt at a fast or slow rate?
Fast
Because it doesn't take that long for them to adapt from low sensitivity to a slightly higher sensitivity
Cones are already low in sensitivity so it doesn't take that long to return back to their normal low sensitivity
98
Transitioning from being in the light from outside and coming into a dark room, do rods adapt at a fast or slow rate?
Slow
Because it takes them a while to adapt from low sensitivity to a much higher sensitivity
Rods are originally high in sensitivity so it takes longer to return back to their normal high sensitivity from low sensitivity
99
Which photoreceptor adapts to the dark after being in the light faster?
Cones
100
Which photoreceptor adapts to the dark after being in the light slower?
Rods
101
Which photoreceptor is responsible for colour vision?
Cones
102
Cones are responsible for...?
Colour vision
103
What are the 3 types of cones (each sensitive to different wavelengths of light)?
1) Red (long wavelengths)
2) Green (medium wavelengths)
3) Blue (short wavelengths)
104
Which type of cone has a long wavelength?
Red
105
Which type of cone has a long medium wavelength?
Green
106
Which type of cone has a short wavelength?
Blue
107
Which type of cone is blue?
Short wavelength
108
Which type of cone is green?
Medium wavelength
109
Which type of cone is red?
Long wavelength
110
Which photoreceptor produces monochromatic vision?
Rods
111
What kind of vision do rods produce?
Monochromatic vision
112
Rods only have 1 type. What wavelength is it sensitive to?
Most sensitive to medium wavelengths (green light)
113
What is it called when the peak luminance sensitivity of the eye shifts toward the blue end of the colour spectrum at low illumination levels as part of dark adaptation?
Purkinje shift
114
At night red looks darker than green. This is known as...?
Purkinje shift
115
Define Purkinje shift
At night, the cones are not working so only the rods are working
Rods produce monochromatic vision and are sensitive to blue-green (between short-medium wavelengths)
Because rods are sensitive to blue-green (between short-medium wavelengths), red (longer wavelengths) will appear darker, whereas blues and greens (shorter wavelengths) will appear brighter
Meaning red objects become more difficult to see at night than blue or green objects
116
True or False?
Photoreceptors are evenly distributed across the retina
False
Photoreceptors are not evenly distributed across the retina
117
Which part of the retina contains only cones?
Fovea
118
What does Fovea contain?
Only cones
119
True or False?
When looking directly at an object the image falls on the Choroid
False
When looking directly at an object the image falls on the fovea
120
True or False?
Everywhere but the fovea contains more rods than cones
True
121
True or False?
The fovea contains rods
False
The fovea contains cones
122
Why are cones concentrated in the centre of our eye (the fovea)?
Because this is the centre of our field of view and the most effective location to have high spatial acuity and colour vision.
123
True or False?
The blindspot has both rods and cones
False
The blindspot has neither rods nor cones
124
When one neuron receives signals from many other neurons
This is known as...?
Neural convergence
125
Which neuron receives signals from other neurons in neural convergence?
Ganglion cell receives signals from multiple photoreceptors
126
Ganglion cell receives signals from multiple photoreceptors
This is known as...?
Neural convergence
127
On average, how many rods send signals to 1 ganglion cell?
120 rods send signals to 1 ganglion cell
128
On average, how many cones send signals to 1 ganglion cell?
6 cones send signals to 1 ganglion cell
129
What determines visual acuity?
Neural convergence
130
The ability to detect fine details of a stimulus is known as...?
Acuity
131
Define acuity
The ability to detect fine details of a stimulus
132
When you are able to detect fine details, you have...?
a. High acuity
b. Low acuity
a. High acuity
133
When you are able to detect only course details, you have...?
a. High acuity
b. Low acuity
b. Low acuity
134
Define low acuity
When you are able to detect only course details
135
Define high acuity
When you are able to detect fine details
136
Which photoreceptors have greater convergence?
a. Rods
b. Cones
a. Rods
137
Which photoreceptors have less convergence?
a. Rods
b. Cones
b. Cones
138
Less convergence = ............. acuity
a. Worse
b. Better
b. Better
139
Which photoreceptors lead to lower acuity?
a. Rods
b. Cones
a. Rods
140
Which photoreceptors lead to higher acuity?
a. Rods
b. Cones
b. Cones
141
Why do rods lead to lower acuity?
Because they have greater convergence
Simply = Multiple rods have to share 1 ganglion cell to send their signals to (slower transmission)
Why = Because there are a lot of rods and not enough ganglion cells for each of the rods to send their signals to
142
Why do cones lead to higher acuity?
Because they have fewer convergence
Simply = Each cone gets their own ganglion cell to send its signals to (faster transmission)
Why = Because there are not that many cones and there are sufficient ganglion cells for each of the cones to send their signals to
143
Where in the eye do we have the highest acuity and why?
Fovea
Because it is concentrated with cones which have less convergence
144
What is foveal acuity used for?
Used for scrutinizing highly detailed objects
145
What is peripheral acuity used for?
Used for organizing the broad spatial scene and for seeing large objects
146
Used for organizing the broad spatial scene and for seeing large objects
Is this foveal or peripheral acuity?
Peripheral
147
Used for scrutinizing highly detailed objects
Is this foveal or peripheral acuity?
Foveal
148
True or False?
Acuity decreases away from the fovea
True
149
What ensures objects of interest are imaged on the fovea in fine detail (high acuity vision)?
Eye-movements
150
Does acuity decrease in low-lighting or bright-lighting conditions?
Low lighting conditions
151
Why does acuity decrease in low-lighting conditions?
- Because cones (needed for high acuity due to less convergence) do not work in dim/dark light
- Only rods work and rods have greater convergence which results in lower acuity
152
Where is the retinal distribution of cones?
Fovea
153
Where is the retinal distribution of rods?
Periphery
154
How many types of cones are there?
3
155
How many types of rods are there?
1
156
Why is it harder to see colour at night?
- Cones (photoreceptors that are responsible for colour vision) don't work at night
- We can only rely on rods which produce monochromatic vision
157
Why is it easier to see stars in the night sky when we don’t look directly at them?
- When you look at stars at night, it is a low amount of light being received by the eye
- This amount of light is too little to stimulate the cones
- But if you look directly at that star, the image of that star will fall on your fovea, where a lot of the cones are concentrated in
- Fovea also does not contain any rods so if you look directly at the star, you can't see it
- But if you look at the star at a certain angle, you are now looking at it in a peripheral view where all the rods are located
158
Why do we move our eyes to look directly at an object we’re interested in?
- So that the image will land on the fovea
- Fovea; allows us to use our cones for high acuity vision and colour vision
159
Why is it hard to see anything when we go from bright sunlight into a dark room?
- Bright light bleaches photopigment important for transduction
- Photoreceptors lose sensitivity in bright light
- When we go into darkness, we initially have poor sensitivity so we can't see anything
- But over time, photoreceptors will recover their sensitivity (dark adaptation)
160
Why does everything look a bit blurry at night?
- Cones (photoreceptors responsible for high acuity due to less convergence) do not work properly at night
- We only use rods which result in low acuity due to more convergence
