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Sensation and Perception > Chapter 2: Light and the Eyes > Flashcards

Chapter 2: Light and the Eyes Flashcards

1
Q

Light

A

visible illumination type of electromagnetic radiation

Light has properties of both a wave and a stream of particles

  • Wave: wavelength is a property if electromagnetic radiation
  • Stream of particles: receptors absorb individual particles photons of light
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2
Q

Visible Light

A

370-730 nm

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3
Q

Optic Array

A

spatial patterns of light rays, entering eyes from different locations in a scene

  • limited by where you are in space and what can reach your eyes
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4
Q

Brightness

A

perceived intensity of light reflected/ emitted

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5
Q

Field of View

A

portion of surrounding space visible when your eyes are in their socket without moving eyes

  • specific eye position is species variant
  • eyes in front of head in humans
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6
Q

Acuity

A

measure of how clearly fine details are seen

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7
Q

The eye is encased in […] layers of membrane

A

The eye is encased in three layers of membrane

  • Sclera: tough outer membrane; white of eyes; keeps junk out of eyes
  • Choroid: middle; contains blood vessels that supply O2 and nutrients to eyes
  • Retina: inner membrane that contains neurons, including photoreceptors
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8
Q

Extraocular Muscles

A

Three pairs of muscles move the eyes (keeps eyes pointed in the same direction)

  • Superior/ Inferior Rectus: moves eyes up and down
  • Medial/ Lateral Rectus: side to side
  • Superior/ Inferior Oblique: rotation of eyes and helps with spatial navigation
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9
Q

Shape and Size of the Eye

A

roughly spherical- 24 mm diameter

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10
Q

Cornea

A

transparent membrane at front of eye that refracts light

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11
Q

Iris and Pupil

A

Iris- colored part of eye; involved in inclusion of light

Pupil- opening in iris

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12
Q

Pupillary Reflex

A

automatic process where iris contracts and relaxes to control size of pupil in response to light

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13
Q

Chambers of Eye

A

Anterior Chamber:

     - Between cornea and iris
     - Filled with aqueous humor

Posterior Chamber:

     - Smaller space between iris and lens
     - Filled with aqueous humor

Vitreous Chamber:

     - Large; main interior portion of eye
     - Filled with vitreous humor
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14
Q

Intraocular Pressure

A

pressure of fluids in chamber of eyes

  • important in glaucoma- too much fluid present
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15
Q

Focal Length

A

distance from a lens at which image of object is in focus when object is far away

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16
Q

Diopters

A

units used to express lens power (1/ focal length)

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17
Q

Lens

A

power of any lens to refract light determines its focal length

   - Weak lens doesn't refract light much (info doesn't make it to retina)
   - Strong lens refracts light sharply
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18
Q

Zonule Fibers

A

connect choroid and lens

- changes lens and shape

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19
Q

Ciliary Muscle

A
  • muscles attached to choroid

- control tension of zonule fibers

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20
Q

Accomodation

A

adjustment of shape of lens so light of object from different distances focuses correctly on retina

  • ciliary muscles are relaxed= choroid pull on zonule fibers= lens become thin and flat (weak lens with long focal length)
  • ciliary muscles are contract= choroid pull on zonule fibers are opposed (stronger lens with shorter focal length)
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21
Q

Retinal Image

A

clear image of optic array on retina

  • image is flipped 180, but is fixed in brain
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22
Q

Optic Disk

A

axons of RGC exit the eye

  • no photoreceptors
  • blind spot
  • no blood vessels
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23
Q

Types of photoreceptor in retina

A

Rods- black and white vision in dim light

Cones- high acuity vision in bright light

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24
Q

Cells in visual system

A

Bipolar Cells

  - receive from photoreceptors
  - send to amacrine cells and RGC

Horizontal Cells
- receives and sends from photoreceptors and other horizontal cells

Amacrine Cells

   - receive and send to bipolar cells and other cells
   - sends to RGC

Ganglion Cell Layer
- layer of retina that contains RGCs

Retinal Ganglion Cells (RGCs)

    - receives from bipolar and amacrine cells
    - sends AP to brain via optic nerve
25
Q

Fovea

A

has no rods but lots of cones

- receives what you’ve paying most attention to

26
Q

Pigment Epithelium

A

has embedded photoreceptors

27
Q

Anatomy of Retina

A

Nuclear Layer

   - Ganglion Cell Layer- RGCs
   - Inner Nuclear Layer- bipolar, horizontal, and amacrine
   - Outer Nuclear Layer- photoreceptors

Synaptic Layer- where retinal neurons make synapses with each other

    - Inner Synaptic Layer- between ganglion and inner nuclear layer
    - Outer Synaptic Layer- between inner nuclear and outer nuclear layer
28
Q

Optic Nerve

A

nerve formed by bundling together axons of RGCs

- exits eye through optic disk

29
Q

Luminance Contrast

A

difference in intensity of illumination at adjacent retinal locations
- due to lateral pathway

30
Q

Photopigments

A

molecule with ability to absorb light and initiate transduction of light with neural signals
- vary in ability to process light

Order:
S-cones
Rods
M- cones
L- cones
31
Q

Spectral Sensitivity

A

degree to which photopigment molecules absorb lights of different wavelengths

32
Q

Photoisomerization

A

change in shape of photopigment molecules between isomers when molecule absorbs a photon
- initiates transduction of light to neural signal

*Photopigment regeneration- occurs after photoisomerization

33
Q

Adapting to Changes in Lighting

A
  • Highest level of light commonly experiences is at least a million times as great as the lowest level
  • Light adaptation- opposite of dark adaptation (dark –> bright environment)
  • Dark adaptation- process of adjusting retinal sensitivity when going from bright–> dark environment
34
Q

Operating Range

A

visual systems sensitivity to range of light intensities in current scene
- visual system adjusts operating range based on current conditions

35
Q

Dark Adaptation

A

picture on phone

36
Q

Convergence

A

property of retinal circuits in which multiple photoreceptors send signals to one RBG

37
Q

Convergence in Retinal Circuits

A

Numerous rods (reasons why rods are more light-sensitive) have to converge ganglion cells much more than do cone (more likely to have 1:1 ratio)

  • Circuits with convergence have a property called spatial summation
    - Firing rate of the RGC increases as the number of photoreceptors that are activated by light increases
  • Degree of convergence affects acuity and firing rate
38
Q

Spatial Summation

A

signals from photoreceptors in same small space on retina add up to affect response of RGC in circuit

39
Q

Receptive Fields

A

Area that, when stimulated, causes a change in the firing rate of a single cell

  • Receptive field vary in size; areas in the fovea are much smaller than areas in the periphery
  • Midget (smaller) and parasol ganglion (larger) cell have different- sized receptive fields
    - Enhance complexity of circuits
40
Q

Preferred Stimulus

A

type of stimulus that produces neuron’s maximum firing rate

41
Q

Center- Surround Receptive Fields

A
  • Can be on- and off- center, with different patterns of response from RGCs
    - On- center: RGCs increase firing rate when light in center is brighter than surrounding
    - Off- center: RGCs increase firing rate when light in center decreases
  • Little change in firing rate when light uniformly covers the center and surround (canceled out)
  • RGCs respond to luminance contrast, not so much to uniform illumination
42
Q

Lateral Inhibition

A

refers to the inhibitory signals sent by horizontal cells, which modify the responses of photoreceptors and provide a way in which neural activity in one part of the circuit can influence neural activity in adjacent parts of the circuit

43
Q

Edge Enhancement

A

process where visual system makes edges visible, helping perception of objects and surfaces

  • detecting boundaries is crucial vision, especially in dim light where differences in brightness at the edges may be very small
  • lateral inhibition works to sharpen boundaries to enhance the process
  • RGCs with center- surround receptive fields that exhibit lateral inhibition (spot detectors) make edge enhancement happen
44
Q

Mach bands

A

changes in intensity near each edge

45
Q

Single-Cell Recording

A

how we are able to see activation

  • edges –> orientation –> form –> motion –> etc
46
Q

Strabismus

A

disorder of extraocular muscles where two eyes aren’t aligned with each other

  • double image; impairs binocular depth perception
47
Q

Amblyopia

A

misalignment of eyes leads to suppression of signals from one eye so fine vision doesn’t develop in that eye

  • eyes develop normally, but signals from one eye aren’t processed properly
48
Q

Myopia

A
  • nearsightedness
  • optic axis- too long
  • can’t make lens thin enough
  • focus in front of retina
49
Q

Hyperopia

A
  • farsightedness
  • optic axis- too short
  • can’t make lens thick enough
  • focus behind of retina
50
Q

Presbyopia

A

lens become less elastic with age
- can’t make lens thick enough

Near Point begins to increase
Near Point- closest distance at which person can bring object into focus

51
Q

Astigmatism

A

curvature of cornea or lens is slightly irregular or asymmetrical, making it impossible for lens to fully accommodate

LASIK- surgery to reshape the cornea in order to correct disorders of accommodation

52
Q

Cataracts

A

progressive “clouding” of lens that can lead to blindness

Causes:

  • exposure to UV radiation
  • diabetes and other diseases
  • aging

Treatment:
- surgery to remove and replace lens (of fixed focal length)

53
Q

Glaucoma

A

intraocular pressure is too high for person’s eye

Cause:
- most commonly caused by blockage of aqueous humor drain from the anterior chamber

Treatment:
- drugs, laser, or surgical therapies

54
Q

Floaters

A

shadows on retina thrown by debris within vitreous humor

- perceived as small, semitransparent spots/ threads that float in front of eye

55
Q

Phosphenes

A

brief, tiny bright flashes person’s field of view not caused by light

56
Q

Macular Degeneration

A

damage to photoreceptors in region at center of retina

  • Dry- no treatment
  • Wet - prescription treatment
57
Q

Retinitis Pigmentosa

A

inherited condition is where there is gradual degeneration of photoreceptors over many years

  • night blindness and tunnel vision
58
Q

Night-Vision Devices

A

Thermal Imaging- uses IR radiation

Image Enhancement- converts photons to electrons then produces patterns of intensities

Sensation and Perception (14 decks)

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