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Perception Midterm > Chapter 2 - The Beginnings of Perception > Flashcards

Chapter 2 - The Beginnings of Perception Flashcards

1
Q

The steps of perception, beginning with physical events

A
  1. Environmental stimulus
  2. Light reflected from tree transforms on the way to visual receptors
  3. Properties of receptors transform light -> electrical signals
  4. Electrical signals are processed in neurons
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2
Q

Light energy

A

The stimulus for vision

A band of energy in the electromagnetic spectrum

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3
Q

Wavelength

A

Energy in the electromagnetic spectrum

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4
Q

Visible light

A 
400 - 700 nm
Associated with different colours
Short - blue
Middle - green
Long - yellow, orange, red
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5
Q

Photon

A

Smallest possible packet of light energy

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6
Q

Primitive eyes

A

Cambrian period
Eyespots on animals
Could only distinguish light from dark, no features
Detailed vision did not evolve until optical systems were created

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7
Q

Describe what happens to light on an object when it enters the eye

A

Light is reflected from the object into the pupil
The cornea focuses and creates an image on the retina
The signals from the receptor flow through neurons in the retina
These neurons emerge from the back of the eye through the optic nerve, and are then sent to the brain

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8
Q

Retina

A

Network of neurons in the back of the eye

Contains receptors for vision

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9
Q

Visual receptors

A

Rods and cones

Contain light sensitive chemicals called visual pigments

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10
Q

Visual pigments

A

React to light and trigger electric signals

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11
Q

How cornea, lens, receptors and neurons shape vision

A

2 transformations

  1. Light from object -> image of object
  2. Image of object -> electrical signals
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12
Q

How is light focused by the eye?

A

2-element optical system: lens and cornea

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13
Q

Cornea

A

Transparent covering of the front of the eye
80% of the focusing power
But fixed in place and cannot adjust focus

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14
Q

Lens

A

20% focusing power
Can change shape to adjust focus
Ciliary muscles increase focusing power by increasing curvature

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15
Q

Why does the eye need to adjust to focus?

A

When looking at a far away object, the light rays are parallel
The cornea and lens bring the rays to focus on the retina
When the object moves closer, the rays are at an angle and the focus point is pushed back
Light is stopped by the back of the eye, so the image on the retina is out of focus

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16
Q

How does the lens accommodate?

A

The ciliary muscles tighten and increase lens curvature
Lens becomes thicker, increases bending of light rays
Eyes are constantly adjusting as you look around because not everything is in focus at once

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17
Q

Loss of accommodation with increasing age

A

Presbyopia - distance of near point increases because the ciliary muscles weaken and cannot focus as well
20 yrs - 10cm, 30 yrs - 14cm, 40 yrs - 22cm, 60 yrs, 100cm

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18
Q

Myopia

A

Nearsightedness - cannot see far away objects

Brings parallel rays into focus in front of the retina instead of the back, so the image is blurred

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19
Q

Causes of myopia

A
  1. Refractive myopia - the cornea/lens bends light too much

2. Axial myopia - eyeball is too long

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20
Q

Solutions to myopia

A
  1. Bring objects closer - push focus point back on retina
  2. Corrective lenses - bends incoming light so it is focused as if it was at the far point
  3. Surgical procedures - LASIK changes the shape of the cornea
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21
Q

Far point

A

Distance where light is focused on retina

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22
Q

Hyperopia

A

Farsightedness - cannot see nearby objects
Focus point for parallel light is behind retina
Usually because eyeball is too short
When older - can cause eye strain and headaches due to constant accommodation

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23
Q

Where does vision occur?

A

Not in the retina; rather in the brain

Light on retina activates visual receptors

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24
Q

What is the relationship between light and visual receptors?

A

Light on the visual receptors triggers electrical signals when absorbed by the visual pigment molecules
These electric signals are transferred to the brain
Visual pigments determine the ability to see dim light, as well as light from different parts of the spectrum

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25
Q

Transduction

A

The transformation of one energy form into another

Vision transduction occurs in rods and cones

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26
Q

Where is the starting point of transduction?

A

The outer segment of receptors where the visual pigment is contained

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27
Q

What are the parts that make up visual pigment?

A

Opsin - long protein
Retinal - smaller, light-sensitive
When they combine, the resulting molecule absorbs visual light

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28
Q

Isomerization

A

When visual pigment absorbs one photon of light, retinal goes from bent to straight
This leads to a chemical chain reaction
Each molecule activates thousands more
This amplifies the effects of isomerization, charging up to a million molecules and activating the receptor

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29
Q

Dark adaptation and light sensitivity

A

After the visual system adapts to the dark, small lights seem brighter because the system is more sensitive
Rods and cones adapt at different rates

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30
Q

Ratio of rods:cones

A

Depends on location in retina
Fovea - only cones, but only 1% of all cones
Peripheral retina - rods (120 million) and cones (6 million)

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31
Q

Macular degeneration

A

Destroys the cones in the fovea and small area around it

Blind region in central vision

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32
Q

Retinis pigmentosa

A

Degeneration of retina from one generation to the next
Attacks peripheral rod receptors and gives poor peripheral vision
In severe cases, foveal cone receptors are also attacked, leading to blindness

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33
Q

Blind spot

A

Area with no receptors, where optic nerve leaves the eye

Brain fills in the spot missing from the blind spot

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34
Q

Dark adaptation curve

A

Function relating sensitivity to light to time in the dark, as soon as the lights are off
Higher sensitivity as time goes on

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35
Q

How do you measure the dark adaptation curve?

A
  1. Have the observer look at a small fixation point
    The image falls on the fovea (C), the test light falls on peripheral retina (R & C)
  2. Measure the threshold for seeing light by turning the knob to adjust the intensity of the flashing light until it is barely seen
    This threshold is converted to sensitivity
    High threshold = low sensitivity
  3. Once adapted, light is extinguished and continues to adjust sensitivity until the flashing light is barely visible
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36
Q

Light-adapted sensitivity

A

Measured when eyes adapt to light

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37
Q

Phases of dark adaptation curve

A
  1. Increases rapidly for 3-4 minutes after light turns off, then levels for 7-10 minutes: CONES
  2. Increases again until about 20-30 minutes: RODS
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38
Q

Dark-adapted sensitivity

A

After 20-30 minutes, eye is 100,000 times more sensitive than light adapted

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39
Q

Eye patches and pirates

A

Keeping 1 eye in the dark triggers the process of dark adaptation

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40
Q

How can you test only cones’ dark-adaptation?

A

Test light is small enough that it only falls on the fovea

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41
Q

How can you test only rods’ dark-adaptation?

A

Some people have no cones (rod monochromats)

Their light sensitivity is determined only by rods

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42
Q

What happens to rods and cones when light is extinguished?

A

Their sensitivity increases
Cones are more sensitive at the beginning, and between 3-5 minutes they are at max sensitivity
Rods are still adapting, and by 7-10 minutes they become more sensitive than cones

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43
Q

Rod-cone break

A

Where rods begin to determine dark adaptation curve

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44
Q

Why do rods take longer than cones to adapt?

A

Visual pigment regeneration occurs faster in cones than rods

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45
Q

Visual pigment bleaching

A

Retinal becomes lighter in colour

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46
Q

Visual pigment regeneration

A

Light causes retinal to change shape, and after it changes it separates from opsin and leads to visual pigment bleaching
As the light remains on, pigment isomerizes and breaks away from opsin
Regeneration occurs when retinal returns to bent shape and reattaches to opsin

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47
Q

What happens to visual pigment molecules in light?

A

Some are isomerizing and bleaching while others are regeneration
In normal light, eye contains BOTH bleached and intact pigment

48
Q

What happens to visual pigment molecules in the dark?

A

Bleached pigment continues to regenerate, but there is no more isomerization
Eventually only unbleached pigment remains
The increase leads to dark sensitivity and dark adaptation

49
Q

Rushton’s procedure

A

Showed relationship between pigment concentration and sensitivity
Measured the regeneration of visual pigment in humans by looking at darkening of the retina during dark adaptation

50
Q

Rushton’s results

A

Showed that cone pigment takes 6 minutes to regenerate
Rod pigment takes more than 30 minutes
Adaptation matches the rate of regeneration

51
Q

2 important connections between perception and physiology

A
  1. Light sensitivity depends on the concentration of visual pigment
  2. The speed at which sensitivity increases in the dark depends on the regeneration of visual pigment
52
Q

Detached retina

A

Retina detaches from pigment epithelium
This prevents visual pigment from regenerating, because retinal and opsin cannot recombine
The person becomes blind in the areas where the retina is detached

53
Q

Spectral sensitivity

A

The eye’s sensitivity to light as a function of the light’s wavelength
Rods and cones respond differently to light in different parts of the spectrum

54
Q

Spectral sensitivity curve

A

Relationship between wavelength and sensitivity

55
Q

How to measure the spectral sensitivity curve

A

Present one wavelength at a time and measure sensitivity (monochromatic light thru a filter)

56
Q

Sensitivity thresholds at different wavelengths

A

Higher - short and long

Lower - middle (less light needed to see these)

57
Q

How to test spectral sensitivity only on rods or cones?

A

Cones - test light only on fovea

Rods - test when the eye is dark adapted

58
Q

Rod spectral sensitivity

A

Most sensitive to 500nm

59
Q

Cone spectral sensitivity

A

Most sensitive to 560nm
3 different cone pigments have their own receptors
S - short-wavelength, best absorption at 419nm
M - medium-wavelength, best at 531nm
L - long, best at 558nm

60
Q

Dark adaptation on spectral sensitivity

A

Leads to more sensitivity to short wavelengths (blue/green)
eg. green foliage stands out in the dark
This occurs because of the shift from cone -> rod vision as the eye adapts to low light

61
Q

Purkinje shift

A

Enhanced perception of short wavelengths during dark adaptation

62
Q

Relationship between rod visual pigment and rod spectral sensitivity curve

A

They match each other

Adding them together results in a curve peaking at 560nm

63
Q

What are dark adaptation and spectral sensitivity determined by?

A

Rod and cone visual pigment properties

Even though perception doesn’t occur in the eye, what we see is affected at this point

64
Q

Key components of neurons

A

Cell body
Dendrites - receive electrical signals
Axon/nerve fiber - filled with fluid that conducts electrical signals

65
Q

What kind of neurons are important for perception?

A

Sensory receptors - specialized to receive environmental stimuli

66
Q

Transmission of signals from retina to neurons

A

100 million+ receptors in retina
Then sent through optic nerve to Lateral Geniculate Nucleus (LGN)
Then to receiving area in the cortex
Individual neurons transmit messages about the tree

67
Q

How are electrical signals recorded from axons?

A

2 small electrodes
Recording electrode - tip inside/just outside neruon
Reference electrode - some distance away
Connected to a meter that records the difference in charge between the electrodes

68
Q

Difference between electrodes during resting potential of axons

A

-70mV (aka resting potential)

This means that the inside of the neuron is 70mV more negative than the outside

69
Q

What happens when a signal passes through neurons?

A

Charge rises from -70mV to +40mV

Then returns to resting level

70
Q

Action potential

A

The change in charge from resting to a signal passing through
Lasts about 1ms

71
Q

Propagated response

A

Once triggered, the signal travels all the way down the axon without decreasing in size
Extremely important - allows signals to transmit over long distances
AP remains the same size no matter the intensity of the stimulus

72
Q

Refractory period

A

The interval between the time one nerve impulse occurs and the next one can be generated
1ms for most neurons

73
Q

What limits the rate of firing in a neuron?

A

The refractory period

74
Q

Upper limit of a neuron, per second?

A

500-800 impulses

75
Q

Spontaneous activity

A

APs which occur before the stimulus is applied
Baseline for firing the neuron
In most cases stimulation increases firing above spontaneous, but sometimes it is less

76
Q

What are neurons bathed in?

A

Ion rich solution

77
Q

How are ions created?

A

When molecules gain/lose electrons

78
Q

What is the solution outside of the neuron?

A

Sodium

Na+

79
Q

What is the solution inside of the axon?

A

Potassium

K+

80
Q

Describe the first step of an action potential

A

Na+ rushes into the axon because the channels have opened, due to selective permeability
This increases the positive charge of the axon

81
Q

Rising phase of an action potential

A

Increases from -70mV to +40mV

82
Q

What happens at 40mV?

A

Sodium channels close and potassium channels open

83
Q

Falling phase of an action potential

A

Potassium rushes in and axon becomes begaive

84
Q

What prevents Na+ and K+ from building up?

A

Sodium-potassium pump

85
Q

Synapse

A

Small space between neurons

86
Q

Neurotransmitters

A

Chemicals stored in synaptic vesicles

87
Q

Receptor sites

A

Sensitive to specific neurons, like keys in a lock

88
Q

What happens when an electric signal reaches a synapse?

A

A chemical process is triggered and produces a new electrical signal in a receiving neuron

89
Q

Excitatory response/depolarization

A

The inside of a neuron becomes more positive
Much smaller than positive action potential
To generate an AP, must have enough excitation

90
Q

Inhibitory response/hyperpolarization

A

Inside of a neuron becomes more negative
Moves charge inside axon away from level of depolarization
Prevents AP generation

91
Q

How is neural firing rate determined?

A

Interplay of excitation and inhibiton
If E > I = high firing
If E < I = low firing

92
Q

What is the purpose of inhibition?

A

Neurons transmit and process info; E & I are both parts of the process

93
Q

Neural circuits

A

Interconnected groups of neurons within retina

94
Q

Signals generated in receptors go to…

A

Bipolar cells

Then ganglion cells

95
Q

Ganglion axons

A

Transmit signals out of the retina into the optic nerve

96
Q

Horizontal cells

A

Receptor signals travel through

97
Q

Amacrine cells

A

Signals travel between bipolar and ganglion cells

98
Q

Neural convergence

A

Occurs when a large number of neurons synapse onto a single neuron
Occurs often in retina - 126million receptors, 1 million ganglion cells
Rods converge more than cones

99
Q

Neural convergence in the fovea

A

Cones have private lines to ganglion cells, which receive signals from only one cone

100
Q

Greater convergence of rods compared to cones…

A
  1. Rods have better sensitivity than cones

2. Cones have better detail vision

101
Q

Dark-adapted rods and vision sensitivity

A

Rods become more sensitive than cones

eg. look to side of star = more sharp because of rod rich peripheral retina

102
Q

Why do rods have greater convergence than cones?

A

Because it takes less light to generate a response for a rode than a cone
5 rod receptors -> 1 ganglion
5 cone receptors -> 5 ganglions
When intensity = 1, rod ganglion has more excitation than cone ganglion

103
Q

Acuity

A

Ability to see details

104
Q

Rod circuit acuity

A

2 spots of light next to each other -> rod signals -> ganglion cell fires
Separating the spots -> 2 separate rods fire -> ganglion cell fires
This provides no info on location of light

105
Q

Cones circuit acuity

A

2 neighbouring cones -> 2 ganglion cells fire

2 separate cones -> 2 separate ganglion cells fire

106
Q

High convergence

A

High sensitivity

Poor acuity

107
Q

Low convergence

A

Low sensitivity

High acuity

108
Q

Problems early in the system

A

Have a critical effect

eg. bad lens = doesn’t matter how amazing computers are

109
Q

Type of energy that enters the eye…

A

Activates certain receptors

eg. honeybee and human look at same flower but see different things

110
Q

Preferential looking technique

A

Determines what infants perceive

They look more at whatever they are more interested in

111
Q

Visual evoked potential

A

Recorded by electrodes over the visual cortex

If the system detects stimuli, a response is evoked

112
Q

Visual acuity throughout life

A

Poor at birth
6-9 months - rapid increase
1 yr - levels off to adult acuity

113
Q

Why do infants have low acuity?

A

Development of receptors
Peripheral retina in infants is fairly adultlike
But the foveal rods are widely spaced and poorly developed

114
Q

Differences between adult and newborn in cones and rods

A

Newborns have a small outer segment and a far inner segment
This leads to less visual pigment and light absorption
Adult cones are long and suited to detail
67% of cones are in an adult’s fovea, only 2% are in a newborns

115
Q

Visual area of newborns

A

Poorly developed

But between 6-9 months, neurons and synapses are being added quickly as cones become more dense

Perception Midterm (5 decks)

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