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Vision Science 2 > Ch. 3: Duplex Retina > Flashcards

Ch. 3: Duplex Retina Flashcards

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1
Q

what is the light adaptation range of the human eye?

A

10 log units

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2
Q

although pupil size constitutes for 1 log unit of light adaptation range, what constitutes the rest?

A

rods and cones

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3
Q

what characterizes scotopic vision? and what photoreceptor mediates it?

A

sensitivity to very dim lights, poor visual acuity (20/200) and absence of color discrimination. Rods

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4
Q

what are the characteristics of photopic vision? and what photoreceptor mediates it?

A

occurs under bright conditions, excellent acuity (20/20) and ability to color discriminate. Cones

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5
Q

what type of vision occurs when both rods and cones are being used?

A

mesopic vision

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6
Q

what type of ending does a rod contain?

A

spherule

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7
Q

what type of ending does a cone contain?

A

pedicle

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8
Q

what photoreceptor contain free-floating discs as they breakaway and migrate outward?

A

rods

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9
Q

how many rhodopsin molecules does each human eye contain (on average)?

A

10^15 molecules per eye

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10
Q

after being bleached, how long would it take 50% of the rhodopsin in the eye to revert to an unbleached state?

A

5 minutes

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11
Q

at what wavelength is rhodopsin most probable to absorb a quanta?

A

507 nm

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12
Q

what is threshold for a stimulus?

A

the minimum amount of energy required for detection of a stimulus

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13
Q

does low threshold indicate high sensitivity?

A

yes

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14
Q

what percentage of quanta from any given stimulus is actually absorbed by rhodopsin?

A

less than 20%

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15
Q

what are the 3 fundamental photopigments in cones?

A

cyanolabe, chlorolabe and erythrolabe

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16
Q

what type of cone is cyanolabe?

A

S-cone (426nm)

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17
Q

what type of cone is chlorolabe?

A

M-cone (530nm)

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18
Q

what type of cone is erythrolabe?

A

L-cone (557nm)

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19
Q

after being bleached how long does it take 50% of cones to revert to unbleached state?

A

1.5 minutes

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20
Q

at what point does the photopic spectral sensitivity curve peak?

A

555 nm

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21
Q

is it true that S-cones make little, if any, contribution to spectral sensitivity?

A

yes

22
Q

what is the photochromatic interval?

A

difference in sensitivity between scotopic and photopic systems

23
Q

where are rods most densely packed and what is the approximate density?

A

20 degrees from the fovea. peak density of 150,000 rods/mm^2

24
Q

is it true that number of cones stays stable as we age, but the number of rods decrease with age?

A

true

25
Q

what percentage of cones are located in the fovea?

A

5% (of the total number of cones in the retina)

26
Q

do the ratio of L-cones to M-cones remain 1:1 for all individuals?

A

no they can range from 1:1 to 16:1

27
Q

in dark adaptation it takes approximately 35 minutes for the eye to become adapted to a dark environment, how rapid is the initial reduction in which the the curve plateau’s at the cone plateau? (420 nm curve)

A

10 mins

28
Q

how long does it take to reach the rod-cone break? (420 nm curve)

A

12 minutes

29
Q

what occurs during the rod-cone break?

A

the point at which rods become more sensitive than cones (prior to this point cones detect the stimulus and after the rods detect stimulus)

30
Q

does cone plateau represent the minimum scotopic threshold?

A

no. it represent the minimum photopic threshold (rods represent scotopic)

31
Q

early in dark adaptation is rhodopsin more likely to absorb a quantum of 465 nm or 610nm?

A

465 nm because sensitivity of scotopic system surpasses that of the photopic system (it would take longer to absorb 610 nm due to the regeneration properties of rhodopsin.

32
Q

T/F? During dark adaptation, the regeneration of photopigment increases the probability of quantal absorptions, thereby increasing sensitivity.

A

true

33
Q

what happens to quantal absorption and threshold when 50% of rhodopsin is bleached?

A

quantal absorption decreases by one-half

absorption increases by factor of 10^10

34
Q

how is increment threshold plotted?

A

performed for background light levels ranging from darkness to brightness, resulting in a light adaptation curve that shows increment threshold as a function of background adapting intensity.

35
Q

in a graph depicting the log of increment threshold, what does Weber’s Law explain?

A

as the background brightness is increased, the increment intensity must be increased such that the ratio of the increment intensity to the background intensity remain constant

36
Q

what percentage of rhodopsin is bleached in rod saturation?

A

only about 10%

37
Q

is the Weber fraction under scotopic conditions 0.015?

A

no it is 0.14.

0.015 represents photopic conditions

38
Q

under what conditions is contrast sensitivity higher?

A

under photopic conditions (0.015)

39
Q

is it true that humans “detect” stimulus better under scotopic conditions?

A

yes

40
Q

why do rods produce great sensitivity but poor resolution?

A

because they are connected in such a manner to sum up information over space

41
Q

T/F? Many cones (more than rods) report to one ganglion cell?

A

False. Many rods report to one ganglion cell

42
Q

what is the difference between sensitivity and resolution?

A

sensitivity: a stimulus is seen
resolution: only one stimulus is seen

43
Q

is it true that the scotopic system has excellent sensitivity yet poor spatial resolution?

A

yes

44
Q

what is the equation for Ricco’s Law?

A

(stimulus intensity)*(stimulus area)= constant

45
Q

which system (photopic or scotopic) has a smaller critical diameter?

A

photopic system has a smaller critical diameter (reflects the reduced spatial summation capability of the photopic system)

46
Q

which system has superior temporal (time-related) resolution?

A

photopic system (able to distinguish 2 flashes of light separated by a brief interval in time)

47
Q

what is the temporal summation period of the scotopic system?

A

100 ms

48
Q

what is significant about Bloch’s Law?

A

multiple flashes presented within this critical duration are not resolved, and only one flash is seen.

49
Q

what is the critical duration of the photopic system?

A

10-50 ms

50
Q

at what angle must a light ray strike a cone to be maximally effective?

A

perpendicular to its surface

51
Q

what is the Stiles-Crawford Effect of the First Kind?

A

light rays that strike cones perpendicular to their surface (pinhole centered) are perceived as brighter than those that do not strike perpendicular to the surface

Vision Science 2 (5 decks)

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