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psychopysics > Light perception > Flashcards

Light perception Flashcards

1
Q

What experimental factors important in light perception?

A
  • -Stimulus location
  • -State of subjects eye- dark adaptation
  • -Wavelength of the test flash-spectral sensitivity curve v lamder
  • -Size of stimulus- spatial summation
  • -Duration of the test flash-temporal summation
  • -pupil diameter
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2
Q

Where is the peak density of cones?

A

centre of fovea

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3
Q

What cones are found at the centre of fovea?

A

L and M cones

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4
Q

What field does the centre of fovea have?

A

small field tritanopia

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5
Q

What do you not find in the centre of the fovea?

A

Rods

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6
Q

Where is the peak density of rods?

A

Eccentricity of 20 degrees from fovea

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7
Q

What two types of cells do you find ?

A

Transient and sustained cells

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8
Q

What are sustained cells?

A

Cells that give sustained response with light falling on them

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9
Q

What cells give sustained response ?

A

Midget cells

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10
Q

What do transient cells do?

A

Cells that only respond to when there is a change in light

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11
Q

What happens in dark adaptation?

A

Very bright light rhodopsin and cone pigments get bleached after 5 mins rods start to recover but cones are morse sensitive so more dominate

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12
Q

What photoreceptors recovery is faster?

A

Faster recovery for cones

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13
Q

How long does it take to reach maximum sensitivity?

A

30- 40 mins

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14
Q

What are the 4 points in dark adaptation? point 1

A

Rods and cones start dark adapting at the same time

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15
Q

What are the 4 points in dark adaptation? point 2

A

the more sensitive systems determines the threshold at any one time

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16
Q

What are the 4 points in dark adaptation? point 3

A

Cones adapt faster than rods 8-10 mins versus 30 mins for rods

17
Q

What are the 4 points in dark adaptation? point 4

A

The lowest threshold obtained with rods is much less than that with cones because they are more sensitive

18
Q

What does the normal retina look like?

A

Orangish

19
Q

Why does the retina look orangish?

A

Photopigments absorb blue-green and bit of yellow light leaving back red-yellow light to be reflected

20
Q

What happens to a bleached retina?

A

Photopigments are saturated and cant absorb any more light. All light reflects back and appears white

21
Q

What is photopigment concentration?

A

How photopigment density can contribute to adaptation

22
Q

What is the recovery time for rhodopsin?

A

Rhodopsin recovery time matches the dark adaptation curve

23
Q

do retinal cells or photopigments cells respond faster to changes?

A

Retinal cells faster than photopigments

24
Q

What wavelength does human eye respond to?

A

380-780nm

25
Q

in dark what would the graph look like?

A

The graph would shift the the left in scotopic conditions

26
Q

what is max response to wavelength of light?

A

555nm

27
Q

How do you get a large receptive field?

A

Large number of rods synapse to single retinal ganglion cells

28
Q

what does rod synapsing to single RGC do ?

A

Leads to spatial summation

29
Q

What do parafoveal cones synapse to?

A

3 RGC

30
Q

What is Ricco’s Law of reaching threshold?

A

Threshold is reached if luminance X area reaches a threshold constant

31
Q

How can you reach same threshold?

A

Lower luminance with a larger area can reach the same threshold

32
Q

what area should the stimulus be?

A

Less than critical area

33
Q

How do our eyes sum information?

A

arriving within 10-100ms

34
Q

Why do we need short temporal summation?

A

So that images don’t build up on top of one another

35
Q

What is Block’s Law?

A

A lower luminance for longer can have all the photons summed to reach threshold

Holds up to a limit- the critical limit (100ms)

36
Q

How many photons can reach threshold for detection?

A

5 to 14 small

37
Q

what is the equation to reach threshold for detection?

A

E=h X u

38
Q

What is the min luminance that can be detected ?

A

0.75 X 10-6cdm-2

5-30%of the darkest night sky

39
Q

What factors does light perception depend on?

A

Stimulus location, brightness, size wavelength and duration

neural factors- adaptation, temporal and spatial summation

psychopysics (10 decks)

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