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Psyb51 Intro to Perception > Unit 2: Optics And The Eye > Flashcards

Unit 2: Optics And The Eye Flashcards

1
Q

What is light

A

wave; a stream of photons, tiny particles that each consist of one quantum of energy
- Can be absorbed, diffracted, reflected, transmitted, or refracted

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2
Q

Absorbed

A

energy that is taken up transformed to other forms of energy

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3
Q

Transmitted

A

energy that is conveyed from one place to another through a transparent medium

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4
Q

Reflected

A

energy that is redirected when it strikes a surface. Usually back to origin

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5
Q

Refraction

A

energy that is altered when it passes into another medium (pencil in a cup)

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6
Q

Defracted

A

bent or having waves that spread out (waves of sound)

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7
Q

Why is light a useful source of information?

A

Can tell if food is edible. Can see danger. Social signals/emotions. Circadian rhythm

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8
Q

Acute vision

A

light is projected onto the retina such that light originating from a single point converges back into a point
- Gives ability to resolve images

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9
Q

6 steps in the evolution of eyes:

A
  1. Start with region of photosensitive cells (everything is blurry)
  2. Depressed/ folded areas allow limited acuity
  3. Pinhole allows for directional sensitivity and limited imaging
  4. Transparent humour develops to protect chamber
  5. Refraction: lens is formed. Allows in more light by refraction
  6. Human eye: cornea forms its own lens = more refraction
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10
Q

Path of light:

A
  1. enters through the cornea (first refractive power)
  2. Aqueous humour (second refractive power)
  3. Iris/pupil
  4. Lens (third refractive power)
  5. Vitreous humour (fourth refractive power)
  6. Focuses on a point on the retina
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11
Q

Optic disc

A

hole that blood vessels and optic nerve passes through

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12
Q

Fovea

A

ditch with no rods. For visual acuity

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13
Q

Ciliary muscles to see far (perpendicular light)

A

muscles are relaxed, lens is stretched, less refractive power needed

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14
Q

Ciliary muscles to see close (bent light)

A

muscles are contracted, lens is relaxed, more refractive power needed

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15
Q

4 optical components of the eye to refract light

A

cornea, aqueous humor, lens, vitreous humor

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16
Q

Emmetropia

A

focus light into a single dot

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17
Q

Myopia

A

near-sightedness. Difficulties seeing things far.Light is focused in front of the retina: Lens cannot be stretched enough or eyes are elongated.

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18
Q

Hyperopia

A

far-sightedness. Light is focused behind the retina. Short eye

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19
Q

Astigmatism

A

cornea is not perfectly shaped round

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20
Q

Cornea

A

the transparent window into the eyeball. Contains no blood vessels or blood (would absorb light). Does have transparent sensory nerve endings to close the eye or produce tears

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21
Q

Aqueous humor

A

watery fluid in the anterior chamber of the eye. Supplies oxygen and nutrients

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22
Q

Lens

A

the structure inside the eye that enables the changing of focus

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23
Q

Iris

A

the coloured part of the eye, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil

24
Q

Retina

A

a light-sensitive membrane in the back of the eye that contain photoreceptors and other cell types that transduce light into electrochemical signals and transmit them to the brain through the optic nerve

25
Q

Vitreous Humor

A

the transparent fluid that fills the vitreous chamber in the posterior part of the eye

26
Q

Cataracts

A

opacity of the lens (supposed to be transparent)

27
Q

Fundus

A

the back layer of the retina (seen through a ophthalmoscope)

28
Q

Two types of Photoreceptors

A
  • rods (night vision), 90 million, none in the fovea
  • cones (daylight, fine visual acuity, and colour), 10 million, concentrated at the centre of the fovea and drop off with retinal eccentricity (distance bw image and fovea)
29
Q

duplex retinas

A

two photoreceptors

30
Q

Which photoreceptor is responsible for the periphery

A

Mostly rods

31
Q

what are the 5 cells in the eye

A
  1. photoreceptor
  2. bipolar cells
  3. ganglion cells
  4. horizontal cells
  5. amacrine cells
32
Q

2 types of visual pigments

A
  1. rhodopsin
  2. for cones S,M,L
    - 5-10, X, 2X
32
Q

visual pigments

A

molecules with two parts. chromophore (captures photons) & opsin (absorbds light of a specefic wavelength)

33
Q

why do cats have good night vision

A
  1. slit eyes = more light
  2. reflective back = more chance of hitting photoreceptors
34
Q

photoactivation

A

when capturing a photon, photoactivation begins.
1. hyperpolarization = more negative inside cell
2. graded potential = electron potential that can vary continuously (action potential = all or nothiing)

35
Q

what cells are a part of the Vertical Pathway

A

photoreceptor, bipolar cells, ganglion cells

36
Q

what cells are a part of the lateral pathway

A

horizontal cells, amacrine cells

37
Q

what are the two types of bipolar cells

A

diffuse bipolar cells: receive input from multiple photoreceptors (rods and peripheral cones)
midget bipolar cells: receive input from a single cone in the fovea

38
Q

midget vs diffuse bipolar - which has higher sensitivity vs higher acuity

A

diffuse = multiple inputs = higher senstiviy but lower acuity
midget = one photoreceptor = lower sensitivity but higher acuity

(a lot of signals = do not know where the signal came from)

39
Q

ON vs OFF bipolar cells

A

ON: responds to light
OFF: responds to darkness

40
Q

Midget Ganglion Cells

A

P ganglion cells:
few inputs from the bipolar to the ganglion

41
Q

Parasol Ganglion Cells

A

M ganglion cells: a lot of inputs from bipolar to the ganglion

42
Q

ON/OFF -center ganglion cells

A

center of ganglion cells responds to light vs darkness

43
Q

P vs M ganglion cells.
Characteristic:
response
sensitivity
receptive field
spatial resolution

A

response:
Midget/P = sustained/continuous
Parason/M = transient (only marks the transition from light to darkness)
sensitivity:
Midget/P = sensitive
Parason/M = insensitive
receptive field:
Midget/P = smaller
Parason/M = larger
spatial resolution:
Midget/P = finer
Parason/M = coarser

44
Q

Midget Pathway

A

few photoreceptors connects to ONE bipolar cell and little convergence to the ganglion cells (P/ midget ganglion cells)

45
Q

Parasol Pathway

A

larger or converging to some bipolar and a lot of convergence to the ganglion cells (M/ parasol cells)

46
Q

Are cells more interested in average light or differences in light

A

differences/contrast

47
Q

mach bands

A

illusory edges. perceive that lines are lighter/darker depending on what is being inhibited/activated by the ganglion cell

48
Q

4 mechanisms for dark and light adaptation. 5th does not adapt but is most important

A
  1. pupil dialation
  2. photoreceptors
  3. photopigment replacement
  4. adaptive circuitry
  5. neural circuitry of the retina
49
Q

Pupil Dialation

A

2mm-8mm (16 fold improvement). quickest adaptation

50
Q

Photoreceptors (in relation to dark and light adaptation)

A

a bump in the curve at 7 minutes because there are two systems that adapt:

Different rates and extents for dark adaptation in cones vs rods
Rods: good for night vision. very low absolute threshold
Cones: small absolute threshold

51
Q

Photopigment Replacement

A

Abundance of photopigments (in darkness)
Bleaching of photopigments (in daylight)

52
Q

Adaptive mechanisms in retina circuitry

A

rods connect to ganglion cells through specialized bipolar and amacrine cells
But during daylight these special amacrines are inhibited = rods not working
Darkness– amacrine cells are not inhibited

53
Q

Neural circuitry of the retina accounts for why we are not bothered by variations in overall light levels

A

The visual system regulates the amount of light entering the eye, and tends to ignore whatever variation in overall light level is left over with the help of lateral inhibition (more interested in contrast)
Luminance contrast vs absolute luminance levels
Light level does not matter, it is the difference in light that matters

54
Q
A

Psyb51 Intro to Perception (2 decks)

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