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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
Q

T/F a bleached molecule will NOT spontaneously revert back to unbleached state

A

False, it will

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26
Q

What is the half life for rhodopsin regeneration

A

5 minutes

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27
Q

Can the scotopic system differentiate color and wavelengths?

A

No

28
Q

What is the minimum amount of energy required for detection of a stimulus

A

Threshold

29
Q

A low threshold indicates a high or low sensitivity

A

High

30
Q

T/F one quantal absorption is sufficient to activate one rod

A

Ture

31
Q

How many quantal absorptions result in detection

A

10, but they must occur within a certain space and time

32
Q

Fewer than 20% of the quanta incident on the retina are absorbed by rhodopsin

A

Know this

33
Q

Cyanolabe

A

Blue
426 nm
S

34
Q

Chlorolabe

A

Green
530 nm
M

35
Q

Erythrolabe

A

Red
5557 nm
L

36
Q

What is the peak of the of the photopic sensitivity curve?

A

555 nm

37
Q

What cones contribute to the photopic spectral sensitivity curve

A

L and M

38
Q

What is the photochromatic interval

A

The difference in sensitivity between scotopic and photopic systems for a given wavelength

39
Q

When is the scotopic system greater than the photopic system sensitivity

A

At all wavelengths EXCEPT long wavelength region

40
Q

T/F photochromatic intervals increase with retinal eccentricity

A

True

41
Q

What is the order of the cones sensitivity in the fovea

A

S>M>L

42
Q

What is the order of the cones sensitivity in the peripheral retina

A

M>S>L

43
Q

What is the purkinje shift

A

As lighting conditions change from scotopic to photopic the wavelength that we are most sensitive to increases from 507 to 555 nm

44
Q

How many cones do we have

A

6 million

45
Q

IS the M and L cone ratio the same in everybody?

A

No, it varies

46
Q

How are the S cones different from teh M and L cones

A

There are a lot less of them (5-10%)

They are not found in the fovea

47
Q

What is dark adaptation

A

Gradual improvement in vision after exposure to a bright adapting light

Recovery is based on the regeneration of photopigment molecules

48
Q

What is the reduction in threshold over a 35 minute period

A

5 log units

49
Q

Rods do not become more sensitive then cones until what percentage of rhodopsin is regenerated

A

90%

50
Q

What is the value for the photochromatic interval?

A

3 log units

51
Q

Slide 38

A

Look at it

52
Q

What is light adaptation

A

The visual systems abiity to adapt to changes in the illumination levels

Can be studied with an increment procedure

53
Q

What are the stages of scotopic light adaptation

A
  1. Dark light
  2. Square root law
  3. Weber law
  4. Rod saturation
54
Q

Is the photopic system more sensitive than the scotopic system?

A

Yes, but he absolute sensitivity is less

55
Q

The Weber fraction for scotopic vision is

A

0.14

56
Q

What is the Weber fraction for the photopic vision

A

0.015

57
Q

Rods are connected in a manner that they do what to information?

What does this do?

A

Sum up info over space.

Greater sensitivity, poor resolution

58
Q

Do rods or cones have greater resolution

A

Cones

59
Q

What is the summing up of information over space

A

Spatial summation

60
Q

Slides 46, 47

A

Pictures

61
Q

_____ system has excellent spatial summation

A

Scotopic

62
Q

______ system has excellent spatial resolution

A

Photopic

63
Q

The ____ system has greater temporal summation

A

Scotopic

64
Q

The ____ system has superior temporal reolsution

A

Photopic

65
Q

Slide 51-52

A

Pictures

Perception (6 decks)

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