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Perception > 9- Duplex Retina > Flashcards

9- Duplex Retina Flashcards

1
Q

T/F the human visual system operates over a remarkably broad range of light levels

A

True

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2
Q

What makes it possible for the human eye to see something very bright and small

A

Pupil

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3
Q

What does the pupil changing its diameter allow us to do

A

Help control the amount of light that falls on the retina

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4
Q

What is the formula for retinal illuminance

A

Td: (nits)(pupil are in mm)

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5
Q

Pupillary diameter changes account for what portion of adaptation

A

1 log unit

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6
Q

What accounts for 9 log untis of adaptation

A

The existence and properties of the rods and cones

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7
Q

What are the conditions of scotopic vision

A

Very sensitive to dim lights
Poor VA (20/200)
No color discrimination
Rods

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8
Q

What are the conditions of photopic vision

A

Poor sensitivity to dim lights
Excellent VA (20/20)
Color discrimination
Cones

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9
Q

What does the existence of rods and cones create

A

Duplex retina

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10
Q

What photoreceptor works under mesopic conditions

A

Both roads and cones

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11
Q

What is the rod photopigment?

Where is it found?

A

Rhodopsin

Outer segment

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12
Q

How many rods in the human eye?

A

120 million

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13
Q

How many disks does a rod have

A

1000

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14
Q

How many rhodopsin molecules are there per rod disk?

A

10,000

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15
Q

How many rhodopsins are there per eye

A

10^15 molecules

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16
Q

How many photons of light can one molecule of rhodopsin absorb

A

1

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17
Q

T/F the absorption on one molecule is sufficient to activate a rod

A

True

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18
Q

What is the first step of vision

A

Absorption of light that hyperpolarizes the photoreceptors

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19
Q

What is the principle of univariance

A

Once a quantum of light is absorbed all information regarding its wavelength is lost

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20
Q

What quanta wavelength has the greatest probability of being absorbed

A

507 nm

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21
Q

T/F the absorption and transmission curves are reciprocal s of each other

A

True

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22
Q

When is a molecule of rhodopsin bleached?

A

When it absorbs ligt

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23
Q

How many quanta of light are needed to bleach a molecule of rhodopsin

A

1

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24
Q

When a rhodopsin molecule is in the bleached state can it capture another quatua?

A

NO, but it will transmit a quanta of light incident on it

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25
T/F a bleached molecule will NOT spontaneously revert back to unbleached state
False, it will
26
What is the half life for rhodopsin regeneration
5 minutes
27
Can the scotopic system differentiate color and wavelengths?
No
28
What is the minimum amount of energy required for detection of a stimulus
Threshold
29
A low threshold indicates a high or low sensitivity
High
30
T/F one quantal absorption is sufficient to activate one rod
Ture
31
How many quantal absorptions result in detection
10, but they must occur within a certain space and time
32
Fewer than 20% of the quanta incident on the retina are absorbed by rhodopsin
Know this
33
Cyanolabe
Blue 426 nm S
34
Chlorolabe
Green 530 nm M
35
Erythrolabe
Red 5557 nm L
36
What is the peak of the of the photopic sensitivity curve?
555 nm
37
What cones contribute to the photopic spectral sensitivity curve
L and M
38
What is the photochromatic interval
The difference in sensitivity between scotopic and photopic systems for a given wavelength
39
When is the scotopic system greater than the photopic system sensitivity
At all wavelengths EXCEPT long wavelength region
40
T/F photochromatic intervals increase with retinal eccentricity
True
41
What is the order of the cones sensitivity in the fovea
S>M>L
42
What is the order of the cones sensitivity in the peripheral retina
M>S>L
43
What is the purkinje shift
As lighting conditions change from scotopic to photopic the wavelength that we are most sensitive to increases from 507 to 555 nm
44
How many cones do we have
6 million
45
IS the M and L cone ratio the same in everybody?
No, it varies
46
How are the S cones different from teh M and L cones
There are a lot less of them (5-10%) | They are not found in the fovea
47
What is dark adaptation
Gradual improvement in vision after exposure to a bright adapting light Recovery is based on the regeneration of photopigment molecules
48
What is the reduction in threshold over a 35 minute period
5 log units
49
Rods do not become more sensitive then cones until what percentage of rhodopsin is regenerated
90%
50
What is the value for the photochromatic interval?
3 log units
51
Slide 38
Look at it
52
What is light adaptation
The visual systems abiity to adapt to changes in the illumination levels Can be studied with an increment procedure
53
What are the stages of scotopic light adaptation
1. Dark light 2. Square root law 3. Weber law 4. Rod saturation
54
Is the photopic system more sensitive than the scotopic system?
Yes, but he absolute sensitivity is less
55
The Weber fraction for scotopic vision is
0.14
56
What is the Weber fraction for the photopic vision
0.015
57
Rods are connected in a manner that they do what to information? What does this do?
Sum up info over space. | Greater sensitivity, poor resolution
58
Do rods or cones have greater resolution
Cones
59
What is the summing up of information over space
Spatial summation
60
Slides 46, 47
Pictures
61
_____ system has excellent spatial summation
Scotopic
62
______ system has excellent spatial resolution
Photopic
63
The ____ system has greater temporal summation
Scotopic
64
The ____ system has superior temporal reolsution
Photopic
65
Slide 51-52
Pictures

Perception (6 decks)

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