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U1 Psychology of Perception 212 > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

define Light

A

A narrow band of electromagnetic radiation that can be conceptualized as a wave or a stream of photons.

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2
Q

define Photon:

A

A quantum of visible light (or other form of electromagnetic radiation) demonstrating both particle and wave properties.

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3
Q

for the purpose of this course what is light considered as

A

a waveform when traveling through space and a photon when hitting something

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4
Q

what is visible light located on in the spectrul

A

UV and IR

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5
Q

what colour is associated with shorter wavelengths

A

blue

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6
Q

what colour is associated with longer wavelengths

A

purple

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7
Q

how does light interact with things

A

Light can be absorbed, scattered, reflected, absorbed, transmitted, or refracted.

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8
Q

what happens when light is absorbed

A

Absorbed: Energy (e.g., light) that is taken up and is not transmitted at all.

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9
Q

what happens when light is Scattered:

A

Energy that is dispersed in an irregular fashion

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10
Q

Scattered: Energy that is dispersed in an irregular fashion.

When light enters the atmosphere, much of it is absorbed or scattered and never makes where

A

to the perceiver.

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11
Q

what happens when light is Reflected:

A

Energy that is redirected when it strikes a surface, usually back to its point of origin

aka when you see a red flower, it is actually a flower absorbing all wavelengths except red because red if being reflected back to you

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12
Q

what heppens when light is Transmitted:

A

Energy that is passed on through a surface (when it is neither reflected nor absorbed by the surface).

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13
Q

what happens when light is Refracted:

A

Energy that is altered as it passes into another medium

think pencil in water, it looks broken

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14
Q

The human eye is made up of various parts: what are they

A
  1. Cornea:
  2. Aqueous humor
  3. Pupil:
  4. Iris:
  5. Crystalline lens:
  6. Vitreous humor:
  7. Retina:
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15
Q

what is the cornea

A

The transparent “window” into the eyeball.

allows light to enter the eye

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16
Q

what is the pupil

A

The dark circular opening at the center of the iris in the eye, where light enters the eye.

because it is a narrow opening, this is what causes the image to flip upside down and left to right before hitting retina

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17
Q

what is the iris

A

The colored part of the eye, a muscular diaphragm, that regulates light entering the eye by expanding and contracting the pupil.

is a muscle; regulates how much light enters the eye through the pupil

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18
Q

what is the crystalline lens

A

The lens inside the eye, which focuses light onto the back of the eye.

flexible, causes most refraction in the eye, allows light to be focused at right place in eye

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19
Q

what is the vitreous humour

A

The transparent fluid that fills the large chamber in the posterior part of the eye.

does nothing to light

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20
Q

what is the retina

A

A light-sensitive membrane in the back of the eye that contains rods and cones. The lens focuses an image on the retina, which then sends signals to the brain through the optic nerve.

where all the ‘magic’ happens

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21
Q

what is the Aqueous humor: (behind the cornea)

A

The watery fluid in the anterior chamber.

light starts to refract here

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22
Q

Refraction is necessary for what

A

to focus light rays onto the retina and this is accomplished by the lens.

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23
Q

what is accomodation

A

The process in which the lens changes its shape, thus altering its refractive power.

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24
Q

Nearby objects require more or less refraction?

A

more

because light rays from near objects diverge more.

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25
Q

what is Diopter

A

The focusing force of a lens can be measured in diopters, i.e. the reciprocal of the focal length.

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26
Q

what is meany by ‘reciprocal of the focal length’

A

if f = 20 cm,
then D = 1/.2 meters
= 5 diopters

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27
Q

what is Focal length

A

Distance between the lens and the point at which light rays converge (the focus).

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28
Q

what happens to accommodation with age

A

maximal accomodation decreases with age (lens cannot contract as much)

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29
Q

what are the problems of refraction (eye problems)

A 
Emmetropia: 
Myopia: 
Hyperopia:
-> Presbyopia  
Astigmatism
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30
Q

what is Emmetropia

A

The happy condition of no refractive error.

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31
Q

what is

Myopia

A

When light is focused in front of the retina and distant objects cannot be seen sharply; nearsightedness.

light is focused before the retina! (in front of where it should be)

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32
Q

what is Hyperopia

A

When light is focused behind the retina and near objects cannot be seen sharply; farsightedness.

light is focused behind retina

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33
Q

what is Presbyopia

A

is a form of hyperopia associated with old age: eventually the lens will loose its elasticity.

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34
Q

what is Astigmatism

A

Unequal curving of one or more of the refractive surfaces of the eye, usually the cornea (cornea will likely be oval or an unevens shape and results in multiple focal points)
-> some of the lines won’t seem to converge on the common focal point, they will seem bent or not converging at centre point

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35
Q

what is Fundus

A

Using the ophthalmoscope, doctors can view the back surface of patients’ eyes, called the fundus

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36
Q

what are 2 things you would see at the fundus

A 
white spot (optic disk)
black/darker spot (Macula)
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37
Q

what is the optic disk

A

The white circle, know as the optic disc, is the point where the arteries and veins that feed the retina enter the eye, and where the axons of the ganglion cells leave the eye towards the brain. This portion of the retina contains no photoreceptor and is therefore “blind”.

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38
Q

what is the Macula

A

The dark spot corresponds to the macula. It is situated in the center of eye (i.e. immediately behind your lens). It contains a high densitity of photoreceptors and it is responsible for central vision

39
Q

what is the Fovea

A

The central part of the macula is called the fovea. It contains almost no blood vessels, and contains a high density of photoreceptors. It is responsible for sharp central vision

40
Q

By contrast with other other cranial nerves, the optic nerve and retina is considered part what

A

the brain.

It is the only part of the central nervous sytem that can be imaged non invasively.

41
Q

what can the retina be used to diagnise

A

Can be used to diagnose certain brain disorders like Alzeihmer’s disease

42
Q

what are Photoreceptors

A

Photoreceptors are located at the back of the retina, close to the pigment epithelium, which provides vital nutrients to the photoreceptors. The foremost layers of the retina are transparent

43
Q

why are photoreceptors at the back of the eye when you would expect them to be near the front

A

because they need lots of nutrients and so they are connected to nerves that feed them from the brain

44
Q

Photoreceptors transduce light energy into what

A

neural energy.

45
Q

what are the 2 types of photoreceptors

A

Rods:

Cones:

46
Q

what do Rods do

A

Photoreceptors specialized for night vision.
- Respond well in low luminance conditions
Do not process color

47
Q

what do Cones do

A

Photoreceptors specialized daytime vision, fine visual acuity, and color.
- Respond best in high luminance conditions

48
Q

are there more cones or rods

A

Much more rods (~90 millions) than cones (~4-5 millions) in your retina

49
Q

where are cones concentrated

A

More cones in your fovea, almost no cones outside of the fovea

50
Q

why do you have poor colour vision in periphery

A

More cones in your fovea, almost no cones outside of the fovea.
This means that you have very poor color vision in your periphery. It may seem as if your entire field of view has full-resolution color, but it does not
Note: except for slice 0.0, large cells are cones

51
Q

what is Visual angle

A

Vision scientists measure the size of visual stimuli by how large an image appears on the retina, not by how large the object is.

Rule of thumb: If you hold your thumb out at arms length, the width of your thumbnail is about 2 degrees of visual angle.

In summary: The visual angle of an object is a function of both its actual size and distance from the observer.

52
Q

The foveal has how many rods

A

none

53
Q

The foveal “rod-free” area is about what degree of visual angle.

A

1

54
Q

The foveal “rod-free” area is about 1 degree of visual angle what does this mean

A

This means that we can’t see much more than thumb at arm’s length in central (foveal) vision!

55
Q

how if light converted to a sensory signal

A

Capturing a photon:

56
Q

what is capturing a phone/how to

A

When light hits a photoreceptor, the process of photoactivation begins.

57
Q

what are the components of Photoreceptors

A

Contain an outer segment (adjacent to the pigment epithelium), an inner segment, and a synaptic terminal

58
Q

Visual pigments are manufactured where in the photoreceptor

A

in the inner segment and then stored in the outer segment

59
Q

what are Photopigment

A

Pigments contain a retinal that captures photons and a protein, called an opsin, whose structure determines the wavelength of light to which the photoreceptor responds

60
Q

what is an opsin

A

retinal that captures photons and a protein

61
Q

what kind of opsin do rods have

A

rhodopsin

62
Q

what kind of opsin do cones have

A

Cones have three different opsins, which respond to long, medium or short wavelengths.

63
Q

what is melanopsin

A

Some photoreceptors contain melanopsin and can monitor ambient light levels and influence our sleep/wake cycle

64
Q

Photopigment molecules have two possible shapes, called what

A

isomers

65
Q

When a photopigment molecule absorbs a photon of light, it undergoes what

A

photoisomerization

66
Q

what is photoisomerization

A

its shape changes from one isomer (11-cisretinal) to the other (all-transretinal).

67
Q

what is Photoisomerization

A

initiates a cascade of biochemical reactions that eventually results in the generation of a neural signal.

68
Q

what is Photopigment

A

regeneration, which constitutes the rest of the visual transduction cycle, transforming the all-transisomer back to the 11-cisisomer

69
Q

give a full summary of transduction fo light cycle

A

Photopigment molecules have two possible shapes, calledisomers.

  • When a photopigment molecule absorbs a photon of light, it undergoesphotoisomerization—its shape changes from one isomer (11-cisretinal) to the other (all-transretinal).
  • Photoisomerization initiates a cascade of biochemical reactions that eventually results in the generation of a neural signal.
  • Photopigment regeneration, which constitutes the rest of the visual transduction cycle, transforming the all-transisomer back to the 11-cisisomer.
70
Q

what is The duplex retina

A

rods and cones have different functions!

71
Q

what is another term for night vision

A

scotopic

72
Q

what is another term for daytime seeing

A

photopic

73
Q

the cycle of regeneration is faster in cones or rods?

A

cones

74
Q

Highest level of light we can see is how high compared to the lowest level of light we can see

A

107 vs 1013 photons per second hit the eye

Highest level of light we can see is a million time more intense than the the lowest level of light we can see

75
Q

what is Dark adaptation

A

When entering a dark room (cinema) after being outside, your visual system slowly adjusts itself.

76
Q

what are the Four mechanisms for dark adaptation:

A
  1. Pupil changes its size; fast, but effects are relatively limited
  2. Rods and cones will gradually become more sensitive to light
    - cones will first gain a lot of sensitivity, but will subsequently level off after 5-8 minutes.
    - rods will steadily increase their sensitivy up to ~25 minutes (This corresponds to the time it takes for photopigments to regenerate in rods and cones)
  3. The duplex retina: rods will take over cones (closely related to 2, just 2 has to do with regeneration so regenerated pigment will star building up in receptors)
  4. Neural circuits enhance contrast, making vision possible regardless of global luminance levels.
77
Q

see messages for graph

A

study and understand it

78
Q

How can we measure the sensitivity of cones separately from rod?

A

Use colored stimuli

Compare stimuli presented in the fovea vs periphery

79
Q

do photoreceptors fire action potentions

A

NO

80
Q

explain action potentials

A
  1. Resting membrane potential of a neuron is normally around – 70 mV. The neuronal is said to be polarized.
    - - There is more positive sodium ions (Na+) outside than positive potassium ions (K+) inside of the cell. (outside has more Na+ than inside)
  2. Activating certain receptors at the surface of the neuron will cause its membrane to depolarize.
    - - positively charged sodium ions enter the cell and bring the membrane potential up to +40mV. (Na+ is let in and it depolarizes)
  3. After the neuron has discharged, positively charged potassium ions will leave the neuron and repolarize.
  4. The sodium-potassium pump swaps potassium for sodium. (reestablish balance at beginning)
81
Q

Once photoactivation starts what happens to photoreceptors

A

photoreceptors become hyperpolarized (negatively charged).

82
Q

what is hyperpolarization

A

hyperpolarization is the opposite of a neuron discharging (or depolarizing). Normally it is associated with inhibition of neuronal activity. The fact that it is associated with the transduction of photon is an exception here.

83
Q

Changes in photoreceptor activation are communicated to where

A

the bipolar cells

84
Q

Changes in photoreceptor activation are communicated to the bipolar cells in the form of what

A

graded potentials

85
Q

Graded potentials vary continuously in what

A

their amplitudes

86
Q

Bipolar cells synapse with what

A

retinal ganglion cells

87
Q

Bipolar cells synapse with retinal ganglion cells, which fire in what form

A

an all-or-none fashion rather than in graded potentials

88
Q

summarize the Transduction of light by photoreceptors

A
  1. Once photoactivation starts, photoreceptors become hyperpolarized (negatively charged).
    • > Note: hyperpolarization is the opposite of a neuron discharging (or depolarizing). Normally it is associated with inhibition of neuronal activity. The fact that it is associated with the transduction of photon is an exception here.

2) Changes in photoreceptor activation are communicated to the bipolar cells in the form of graded potentials.
Graded potentials vary continuously in their amplitudes.

3) Bipolar cells synapse with retinal ganglion cells, which fire in an all-or-none fashion rather than in graded potentials.

89
Q

what is the Receptive field

A

The region on the retina in which stimuli influence a neuron’s firing rate.

90
Q

Receptive fields have what kind of organization

A

center-surround organization

91
Q

Receptive fields have a center-surround organization what is this in simple terms

A

ON/OFF or OFF/ON

92
Q

Receptive fields have a center-surround organization (ON/OFF or OFF/ON)
what does this allow for

A

This allows to increase contrast

93
Q

Receptive fields have a center-surround organization (ON/OFF or OFF/ON)
what does the organization depend on

A

This organisation depends on horizontal cells

U1 Psychology of Perception 212 (18 decks)

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