9- Duplex Retina Flashcards Preview

Perception > 9- Duplex Retina > Flashcards

Flashcards in 9- Duplex Retina Deck (65):
1

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

True

2

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

Pupil

3

What does the pupil changing its diameter allow us to do

Help control the amount of light that falls on the retina

4

What is the formula for retinal illuminance

Td: (nits)(pupil are in mm)

5

Pupillary diameter changes account for what portion of adaptation

1 log unit

6

What accounts for 9 log untis of adaptation

The existence and properties of the rods and cones

7

What are the conditions of scotopic vision

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

8

What are the conditions of photopic vision

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

9

What does the existence of rods and cones create

Duplex retina

10

What photoreceptor works under mesopic conditions

Both roads and cones

11

What is the rod photopigment?
Where is it found?

Rhodopsin

Outer segment

12

How many rods in the human eye?

120 million

13

How many disks does a rod have

1000

14

How many rhodopsin molecules are there per rod disk?

10,000

15

How many rhodopsins are there per eye

10^15 molecules

16

How many photons of light can one molecule of rhodopsin absorb

1

17

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

True

18

What is the first step of vision

Absorption of light that hyperpolarizes the photoreceptors

19

What is the principle of univariance

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

20

What quanta wavelength has the greatest probability of being absorbed

507 nm

21

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

True

22

When is a molecule of rhodopsin bleached?

When it absorbs ligt

23

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

1

24

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

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

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