# 11 Light Sensitivity & Spatial Resolution Flashcards

1
Q

Why do we have two photoreceptors?

A

Our species lives on a planet that has day and night

Slide 1

2
Q

If more than one photons was needed to activate one receptor they would have to be ________

A

synchronous

Slide 2

3
Q

For a rod that needed two photons to respond, light intensity has to increase

A

102,000

Slide 2

4
Q

Chances of two photons captured by the same rod at the same time ( within 100 ms) ?

A

once every 16 years

Slide 2

5
Q

Dim light is _____

A

NOISY. We can very reliably distinguish objects from one from the other.

Slide 3

6
Q

Objects (at day and night) are seen against a _______ background

A

Noisy

Slide 4

7
Q

What stops noisy background noise?

A

All the physiology we have talked about (horizontal cells, etc)

Slide 4

8
Q

Rods are _____ but they are _______

A

noisy, reliable

Slide 5

9
Q

Why are rods so noisy?

A

They fire spontaneously, even when they do not have a photon to activate them

Slide 5

10
Q

Rods fire spontaneously every _____ minute(s).

A

2

Slide 5

11
Q

what does “eigengrau” mean?

A

Spontaneous activity (in German)

Slide 5

12
Q

In the picture in Slide 5 there are 3 colors. What does each mean?

Black =
Red =
Green =

A

Photon catch on rod of:

```black = star
red = sky
green = eigengrau, rod pretends to catch photon```

Slide 5

13
Q

***Picture in slide 6, important concept.

Rods will _________

A

saturate

Slide 6

14
Q

Rods will capture to 1, 2, 3 photons and _____ their amplitude of response.

At some point rods will _______ and stop increasing the amplitude of response.

A

increase, saturate

The rod cannot keep increasing their respond because what if 100 photons hit it? No….

Slide 6

15
Q

If rods saturate, what does this mean for day light?

A

They are at their max response rate

16
Q

Dynamic range of rods is ____ log units?

A

6

17
Q

Summing responses of photons in rods is ___ log units?

A

2

18
Q

A single rod can pick up a single photon within ___ seconds

A

30

19
Q

In what conditions do rods do their best?

A

Dim light

20
Q

Rods help detect slight gradations in what color?

A

Black/Grey

21
Q

True/False: Rod bipolar cells receive the response from a single photon from a single rod (or from upwards of 200 photons from 10-15 different rods) and scales it before relaying the signal

A

True

22
Q

Cones can respond to ________ photons/s catch rate

A

1,000000

23
Q

Cones respond in ____ms and sum responses above rate of ____photons/s

A

50, 20

24
Q

Cones have a dynamic range of ______

A

50,000

25
Q

True/False: Rods are less sensitive to a single photon than cones

A

False

26
Q

How reliable is a rod’s response as compared to a cone’s response?

A

With rods, a single rod can receive a signal from a single cone. A cone may respond to a single photon about 5% of the time.

27
Q

True/False: There is no overlap when cones pick up where rods begin to fail

A

False

28
Q

What conditions are photopic, mesopic, and scotopic?

A

Daylight (no rods), intermediate (between thresholds), and very dim light (only rods)

29
Q

Are rods or cones more reliable?

A

Rods (saturate more quickly)

30
Q

What will saturate both rods and cones?

A

A flash of light

31
Q

What will allow cones to operate at any light level?

A

32
Q

Why is photoisomerization rate is limited to 1,000,000/s?

A

Regeneration of visual pigment molecules

33
Q

True/False: Like humans, all vertebrate cones do not saturate with steady light.

A

True

34
Q

True/False: All vertebrate rods detect single photons and can saturate

A

False

35
Q

Slide 14

MAR

A

minimum angle of resolution (1 degree = 60 minutes)

36
Q

Slide 14

Human acuity threshold

A

about 30 seconds (0.5 minutes of arc); note: 360 deg, 60 min per deg, etc.

37
Q

Slide 14

0.5 minimum angle corresponds

A

2.5 micrometers on the retina

38
Q

Slide 14

Max VA of most humans

A

20/15 or 20/10 because of the size of receptive fields

39
Q

Slide 14

Visual angles

A

Smaller when you are farther away from target; Bigger when you are closer to target

40
Q

Slide 15

Contrast Sensitivity Stimuli

A

Contrast sensitivity and spacial frequency are closely related

41
Q

Slide 16

Spacial frequency – Humans VS Cats

A

Humans are good at seeing spacial frequency grading in 2-6 cycle per degree range. Our VA is better than that of a cat

42
Q

Slide 16

Spacial frequency 2

A

Cat Spacial frequency max out at 5-10 c/degree; humans max out at 60 cycles/degree

43
Q

Slide 16

VA of a cat

A

Cats are myopic compared to humans; they can’t see far

44
Q

Slide 16

logMAR

A

A logMAR of 1 equals 0 (equiv. of 20/20 Snellen); logMAR of 0 equals a NEGATIVE number (i.e 20/10)

45
Q

Slide 17

Vernier Acuity

A

Very different from MAR. Requires good binocular vision; tests to see how well the 2 eyes are coordinating to line things up and organize perception in space of information coming in both eyes

46
Q

Slide 17

Ambloypia

A

Can be improved with practice and training

47
Q

Slide 19

Low Vision Chart

A

Letters are getting bigger as you deviate from the center. The chart is normalizing VA based on visual angle displacement; VA is much worse in the peripheral field

48
Q

Slide 20

What is the target/goal behind viewing desaturated color dots with one’s peripheral vision?

A

It get to be a very difficult task for the person to do so and very inaccurate because of the desatutarion of the object color and because of the lack of focus

49
Q

Slide 21

Can we detect a deficiency of cone density on the retina?

A

yes, through a model presented on this slide, because of the patient’s lack of detecting desaturated colors.

50
Q

Slide 21.

what does a simple behavioral test do?

A

detect cone damage.

51
Q

Slide 22

How are acuities measured as?

A

angular resolution.

52
Q

Slide 22

What is angular resolution?

A

it’s the size of the gap (of the C).

53
Q

Slide 22

What is a movement of a target detected by?

A

motion of the target within a certain range.

54
Q

slide 22.

motion detection is detected by what?

A

parasol cells

55
Q

Slide 23.

does spatial resolution decreases with increased visual eccentricity?

A

yes.

56
Q

Slide 23.

what decreases minimum angle of resolution?

A

visual eccentricity

57
Q

Slide 24.

does color resolution decreases with visual eccentricity?

A

Yes

58
Q

Slide 25.

what does receptive fields increase with?

A

visual eccentricity

59
Q

Slide 25.

what drives visual acuity?

A

the size of receptive fields