Vision Flashcards
(142 cards)
1
Q
Scotopic vision lacks both the ____ and _____ of photopic vision
A
Detail
Colour
2
Q
Which out of photopic and scotopic vision has the greatest colour and detail?
A
Photopic
3
Q
Two key properties of sensory systems
A
Feature detection
Adaptation
4
Q
The transformation of electromagnetic radiation to neural impulses is known as
A
Transduction
5
Q
What is transduction in relation to vision?
A
Electromagnetic radiation (light) –> neural impulses
6
Q
The electromagnetic spectrum is made up of
A
Wavelengths visible to humans
7
Q
Transduction, generally speaking, is
A
Conversion of one form of energy to another
8
Q
Iris
A
Contractile tissue that regulates light input
9
Q
How does the iris adjust light input?
A
By adjusting pupil size
10
Q
What is pupillary light reflex?
A
Pupillary contraction/dilation controlled by light entering the eye
11
Q
What does the iris muscle/pupil do in darkness?
A
Iris relaxes
Pupil delates
12
Q
If the pupil dilates, does more or less light enter the eye?
A
More
13
Q
Iris muscle relaxes & pupil dilates
Sensitivity – >
Acuity –>
A
Improves
Decreases
14
Q
If the pupil gets smaller, ______ light enters the eye
A
Less
15
Q
Iris muscle constricts and pupil gets smaller
Sharpness –>
Acuity –>
A
Improves
Improves
16
Q
Tradeoff between _____ and ______
A
Acuity
Sensitive
17
Q
Light
In darkness, each point projects to a larger area. These areas…
A
Overlap
Create blurring
18
Q
Light
In lightness, less light is able to enter the eye. Each point projects to…
A
A smaller and more discrete area
19
Q
Light
In lightness, less light is able to enter the eye. Each point projects to a smaller area. As a result,
A
There is less blurring
20
Q
Where is the cornea situated?
A
Front of the eye
21
Q
What does the cornea do?
A
Focuses incoming light
22
Q
Where is the lens found?
A
Behind the pupil
23
Q
Behind each pupil is a lens, which focuses incoming light on the….
A
Retina
24
Q
Each lens is held in place by suspensory ligaments called
A
Zonules
25
The lens can change shape to change the focal distance of the eye, a process called
Accommodation
26
Accommodation is
Where the lens changes shape
Changes focal distance
27
Focusing
When we direct our gaze at something near, the tension
Holding each lens in place is adjusted by ciliary muscles
28
Focusing
If the lens is rounder, it reduces the....and creates a....
Focal distance
Sharper image
29
Focusing
What does the lens look like if focal distance is reduced and the image is sharper?
Rounder
30
Focusing
What does the lens look like at its weakest/thinnest?
Flatter
31
Focusing
What does the lens look like when focal distance is INCREASED to create a sharper image for distant objects?
Flatter
32
The retina contains a layer of....
Photoreceptive cells
33
The photoreceptive cells of the retina convert light into
Neural signals
34
What is found at the centre of the retina?
Macula
35
In the macula, there is a high concentration of....
Photoreceptor cells
36
What is the site of our sharpest vision?
Fovea
37
What is found at the centre of the MACULA?
Fovea
38
Age-related macular degeneration is the loss of
Central vision
39
Where is the highest concentration of photoreceptor cells found?
Macula
40
When you fixate on something, you are positioning it on the..
Fovea
41
Fovea
Rods/cones
Cones
42
Fovea
What is found on the fovea?
High density of cones
43
Fovea
How is distortion minimised?
Blood vessels/other cells displaced to the side
44
Why is it difficult to see things when you focus on them in darkness?
Fovea --> responsible for focusing
Only cones on the fovea
45
The blind spot is a...
Gap in the receptor layer
46
Blind spot
To minimise this problem, the brain uses...
Completion
47
What is completion?
Information provided by the receptors around the blindspot are used to fill the gap
48
Instead of extracting all visual information, the visual system extracts....
Key information, e.g. edges/location
49
What is the sclera
White layer of eye
| Tough/protective
50
What is the choroid (3)
Layer of tissue between retina/sclera
Contains many blood vessels
Provides oxygen/glucose to retina
51
When we get 'red eye' in pictures, what is it?
Flash reflected off blood in choroid
52
Why is the eye anatomy of vertebrates inverted?
Space saving solution
53
Three main layers of cells in the retina
Photoreceptors
Bipolar cells
Retinal ganglion cells
54
Two types of photoreceptors in the retina
Rods
| Cones
55
Species active in the day tend to have
Cone-only retinas
56
Species active only at night tend to have
Rod-only retinas
57
Species tend to have differing rod/cone levels according to when they are most active. From this observation emerged...
Duplexity theory
58
Rods are responsible for _____ vision
Scotopic
59
Cones are responsible for ______ vision
Photopic
60
Rods operate in ____ lighting
Low
61
High convergence of rods, which means...
Poor acuity
| Good sensitivity
62
Theres only one type of rod -->
Monochromatic
63
Darkness --> rhodopsin inactive --> (3)
1. Na+ channels open
2. Rod depolarised
3. Release glutamate
64
Lightness --> rhodopsin active --> (4)
1. Na+ channels close
2. Rod hyperpolarised
3. No glutamate released
4. Bipolar cell depolarised
65
Blue cones --> ___ wavelength
Short
66
Red cones --> _____ wavelength
Long
67
A SINGLE photoreceptor provides only ______ information
Greyscale
68
2 photoreceptors allow you to
Distinguish wavelength from intensity
69
COLOUR is encoded by differential...
Activation of 2 or more photoreceptors
70
Most people are trichomats, having
3 types of cone
71
__% of men have colour vision deficiency
8%
72
In most cases of colour blindness, it leads to....(2)
Altered sensitivity in one of the cones, or absence
73
Majority of cones are crammed into the
Fovea
74
Fovea
Full of rods/cones
Cones
75
How many fixations are made by the eye per second?
3
76
3 fixations are made by the eye per second. The visual system then...
Integrates this information to produce wide-angled, high acuity, coloured perception
77
Bipolar cells process
Input from the photoreceptors
78
What is the output of bipolar cells?
Retinal ganglion cells
79
Bipolar cells allow _____ signal processing to occur in the retina
Low-level
80
Bipolar cells allow low-level signal processing to occur, aided by
The interneurons
81
Photoreceptors converge via ______ onto retinal ganglion cells
Bipolar cells
82
Few-to-one convergence for _____
Cones
83
Many-to-one convergence for ______
Rods
84
Few-to-one convergence for cones, which maintains
Excellent resolution
85
MACH bands illusions are mediated by
Horizontal cells
86
Mach bands
The apparent change in lightness between bands is an illusion called
Lateral inhibition
87
Two properties of light
Wavelength (colour)
| Intensity (brightness)
88
Binocular disparity is the
Difference in position of the same image on the two retinas
89
Binocular disparity is greater for
Close objects
90
Binocular disparity is least for
Distant objects
91
For a bundle of retinal ganglion cell axons to leave the eye, there must be a gap in the receptor layer -->
Blind spot
92
2 problems with an 'inside out' retina?
Distorted image
| Blindspot
93
A problem with the inside-out retina is that the image is distorted. Which part of the eye corrects this?
Fovea
94
What is the Purkinje effect?
Visual effect --> see more blue colours in darkness
95
Humans have a photooptic spectral sensitivity curve and
A scotopic spectral sensitivity curve
96
The reason our vision doesn't vanish every time we blink?
Temporal intergration
97
"Small jerky eye movements or flicks"
Saccades
98
Saccades are critical for vision function because
The image will fade otherwise
99
Breakthrough in visual transduction came with the discovery of
Rhodopsin (red pigment that absorbs light, extracted from rods)
100
What happened to rhodopsin when it was exposed to intense light?
Bleached and lost ability to absorb light
101
When was Rhodopsins ability regained?
Darkness
102
What protein is the first step in rod-mediated vision?
Rhodopsin
103
The absorption of rhodopsin is related to the ability
To view different light wavelengths
104
Having subjects judge the relative brightness of different wavelengths is a way of measuring
Scotopic spectral sensitivity
105
Most informative feature of any visual display?
Edges
106
5 step process of transduction?
Light --> Photopigment --> Bipolar --> Ganglion --> Leave eye through optic nerve
107
Light is converted into what signals?
Neural
108
The process of adjusting lens configuration (to bring images into focus) is called...
Accommodation
109
Binocular disparity is greatest for...
Close objects
110
Visual system uses information provided by receptors around the blind spot, a process called
Completion
111
A completion process
| Visual system extracts info about edges and infers appearances of large surfaces...
Surface interpolation
112
Involuntary eye movements (3)
Tremors
Drifts
Saccades
113
What is the retina-geniculate striate pathway?
Retina --> primary visual cortex VIA LGN (thalamus)
114
How many layers are there in the LGN?
6
115
There are 6 layers in the LGN. What does each layer receive?
3 receive input from one eye
| 3 from the other
116
Lateral inhibition is the finding that when...
A receptor fires, it inhibits its neighbours via lateral neural network
117
When is lateral inhibition greatest?
When receptor is most intensely illuminated
118
Hubel + Wiesel identified the
Receptive field of a visual neuron
119
"The area of the visual field within which it is possible for a visual stimulus to influence firing of that neuron"
Receptive field
120
Hubel + Wiesel found that all neurons were _______
Monocular
121
Hubel + Wiesel found that all neurons were monocular. This means
Each neuron had a receptive field in one eye but not the other
122
Light shone --> produces "on firing" or "off firing" this dependent on whether the cells were
Off centre
| On centre
123
On centre cells respond to
Light shone in central region
124
On centre cells respond to light shone in the central region of receptive field with
On firing
125
Off centre cells respond to
Light shone in periphery
126
On and off centre cells respond best to
Contrast
127
________ neurons are exceptions to the visual field rule (receptive cells).
Striate cortex neurons
128
Striate cortex neurons fall into one of two classes:
Simple cells
| Complex cells
129
Simple cells - what is the receptive field?
On/off
| Borders are straight lines
130
How to simple cells differ from on/off centre cells?
Borders are straight lines rather than circles
131
Complex cells respond to stimulus of
A particular ORIENTATION
132
Binocular --> respond to stimulation of
Either eye
133
Organisation of the primary visual cortex (2)
1. Functional vertical columns
| 2. Neurons in same column respond to stimuli applied to same area of retina
134
Colour constancy is a tendency for
An object to stay the same colour despite changes in wavelength
135
FIRST STEP in the brain for visual processing?
Primary visual cortex
136
Primary visual cortex is the first step in the brain for visual processing. After that, functions become more _____
Complex
137
After the primary visual cortex, signals travel to the
Secondary visual cortex and visual association cortex
138
After the secondary visual cortex --> output to 2 streams
Dorsal stream
| Ventral stream
139
Dorsal stream specialises in
Visual spatial perception, "where"
140
Ventral stream specialises in
Visual pattern recognition, "what"
141
Scotomas are caused by damage to the
Primary visual cortex
142
"Ability of patients to respond to visual stimuli in their scotomas despite no conscious awareness"
Blindsight
