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Perception > Task 2 > Flashcards

Task 2 Flashcards

1
Q

Visible light - Definition

A

Visible light: energy within the electromagnetic spectrum that humans can perceive
- humans can perceive wavelengths from 400 to 700 nanometers

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2
Q

The Eye

- Cornea

A
  • light enters eye through cornea

- no blood vessels (=transparent) —> photons d not get reflected/absorbed

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3
Q

The Eye

- Lens

A
  • no blood supply (=transparent)

- control process (accommodation) to prevent blurring

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4
Q

The Eye

- Retina

A
  • contains photoreceptors responsible for receiving image from lens and send it to the brain through the optic nerve
  • brings light into focus
  • detects light and communicates to brain the aspects of light related to objects in the environment
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5
Q

The Eye

- Iris

A
  • gives eye distinctive color
  • controls size of pupil and the amount of light that reaches the retina
    • pupillary light reflex: automatic expansion or contraction when level of light increases or decreases, that allows either more or less light to enter the eye
  • attached to ciliary muscles
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6
Q

The Eye

- Pupil

A
  • circular opening in the middle of the iris

- responsible for letting light in and to get it to the lens

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7
Q

The Eye

- Aqueous Humor

A
  • fluid that fills space behind the cornea
  • supply of oxygen and nutrients to cornea and lens
  • removes waste from cornea and lens
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8
Q

The Eye

- Vitreous Humor

A
  • gel-like fluid that fills the vitreous chamber
    • vitreous chamber: longest part of journey through eyeball
  • light refractor: to reach retina, light goes through vitreous chamber, where it is refracted by vitreous humor
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9
Q

The Eye

- Fovea

A
  • part in center of retina responsible for producing the highest visual acuity and point of fixation
  • specialized for seeing fine detail, reading and identifying objects
  • only two cones in the fovea
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10
Q

The Retina

- Fundus

A
  • back layer of the retina

- only place where veins and arteries can be seen directly

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11
Q

The Retina

- Optic Disc

A
  • point where arteries and veins responsible for feeding the retina, enter the eye
  • point where axons of ganglion cells leave the eye via the optic nerve
  • contains no photoreceptors
    • blind spot: area in retina where there are no receptors
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12
Q

The Retina

- Photoreceptors

A
  • light-sensitive receptors in last layer of retina — must be close to pigment epithelium and other neurons
  • help transducing light energy to neural energy
  • capture light and initiate seeing by producing chemical signals
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13
Q

The Lens

- Accommodation

A
  • change in lens‘ shape that occurs unconsciously when ciliary muscles tighten and increase curvature of lens
    • eye constantly adjusting focus with this process
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14
Q

The Lens

- Persbyopia

A

condition that occurs when a person gets older, where the distance of the near point increases
- because lens hardens with age and ciliary muscles become weaker

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15
Q

The Lens

- Myopia

A

(Nearsightedness) —> people are unable to see distant object clearly
- reason: myopic optical system brings parallel rays of light into focus at point in front of retina

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16
Q

The Lens

- Hyperopia

A

(Farsightedness) —> people are unable to see nearby objects clearly
- focus point —> located behind retina because eyeball is too short

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17
Q

Retinal Information Processing

A

Retina contains 5 major classes of neurons: photoreceptors, horizontal cells, amacrine cells, bipolar cells, and ganglion cells

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18
Q

Photoreceptors

A

human retina consists of two types of photoreceptors - rods and cones - with different shape, function and distribution

19
Q

Photoreceptors

- Rods

A
  • sensitive photoreceptors that can only be activated by a single photon
  • depolarized at night - specialized for night vision
    • releases inhibitory neurotransmitter at night
  • photogigment Rhodopsin
  • only one type
  • high convergence, low acuity and high light sensitivity (=slow response)
  • slow regeneration of pigments
20
Q

Photoreceptors

- Cones

A
  • mostly present in fovea
  • specialized for daylight and vision because of low sensitivity but high acuity
  • need light in order to be activated
  • three photopigment:
    • S-cones: blue
    • M-cones: green
    • L-cones: red
  • receptive fields bigger than those of rods
  • little convergence, high acuity and low light sensitivity (=respond fast)
21
Q

Photoreceptors

- Third Type

A
  • contains melanopsin — photopigment sensitive to ambient light
  • involved in adjusting circadian clock
22
Q

Characteristics of Photoreceptors

A
  • information passed to bipolar cells via graded potential

- consist of an outer segment, inner segment, and synaptic terminal

23
Q

Light Transduction by Receptors

A
  1. Photoactivation
    - activation by light that initiates a chain of biochemical events that lead to an overall hyperpolarization of the cell
  2. Hyperpolarization
    - increase in membrane potential —> makes inner membrane surface more negative than outer one
  3. Closing of calcium channels at synaptic terminal
  4. Decrease of glutamate concentration
    - signals bipolar cell, that rod captured photon; hyperpolarization in photoreceptors causes depolarization in bipolar cells
24
Q

Horizontal Cells

A
  • produce inhibitory neurotransmitter GABA
  • form lateral connections between photoreceptors and cause lateral inhibition
  • important for center-surround organization of ganglion receptive fields and for perception of visual contrast
  • in contact with nearby photoreceptors and bipolar cells
25
Q

Amacrine Cells

A
  • many different types, produce different neurotransmitters, mostly inhibitory
  • found in inner synaptic layer where they connect bipolar cells with ganglion cells
  • present in cone and rod pathway, thus, it sometimes combines input from these pathways
  • involved in contrast enhancement and temporal sensitivity, detection of movement and temporal sensitivity
26
Q

What is Lateral Inhibition?

A
  • antagonistic neural interaction between adjacent regions of the retina
  • important for: visual perception and illusion, perceiving contrast
27
Q

Bipolar Cells

- Diffuse bipolar cells

A

Bipolar cells: function as kind of mediator
Diffuse bipolar cells: processes are spread out, so they can receive information from multiple cones
- sensitivity increased by gathering information from many photoreceptors
- visual acuity falls off rapidly with eccentricity

28
Q

Bipolar Cells

- Midget bipolar cells

A

Midget bipolar cells: cells in fovea that receive input from single cone and pass it on to single ganglion cell
- in foes: no convergence (high acuity, low sensitivity to light)

29
Q

Ganglion Cells

A

cells responsible for the process of visual information received from the photoreceptors to the brain (visual cortex) and midbrain (thalamus)

30
Q

Receptive Fields

A

= region of the retina in which stimuli influence a neuron‘s firing rate; can be either excitatory or inhibitory

  • each ganglion cell has its own receptive field:
    • ON-Center cell —> cell that depolarizes in response to increase in the light intensity in receptive-field center
    • OFF-Center cell —> cell that depolarizes in response to decrease in the light intensity in receptive-field center
31
Q

P Ganglion Cells

A
  • smaller receptive field (do not converge, connected to one photoreceptors)
  • sustained firing when light shines on excitatory regions
  • transmit information about contrast in retinal image
32
Q

M Ganglion Cells

A
  • bigger receptive fields (converge); more sensitive under low-light conditions
  • respond more transiently, with brief bursts of impulse when the spot of teh receptive field is turned on; then, they quickly return to spontaneous state
  • transmit information about how this image changes over time
33
Q

Center-Sourround Receptive Fields

A

= each optic nerve fiber monitors a small area of the retina and together they take in information about what is happening over the entire retina
- Center-surround organization: area in ‚center‘ of receptive field that responds differently to light than area in teh ‚surround‘ of the field

34
Q

Transduction

+ Isomerization

A

Transduction: transformation of one form of energy into another form of energy, that occurs in the rods and cones

  • visual pigments contained in outer segments of these receptors; two parts:
    • opsin — large protein
    • retinal — small light-sensitive component
      • when combined, it results in a molecule that absorbed visible light
        • Isomerization: change of shape in retinal that occurs when visual pigment absorbs one photon of light
35
Q

Dark Adaptation

- Definition

A

= process of increasing sensitivity in the dark

- rod and cone receptors adapt to light at different rates because of difference in their visual pigments

36
Q

Dark Adaptation

- Distribution of Rods and Cones

A

fovea: only cones
peripheral retina: all of the retina outside of fovea; more rods than cones
blind spot: no receptors

37
Q

Dark Adaptation

- Measuring Dark Adaptation Curve

A

Dark adaptation curve shows the function relating sensitivity to light to teile in the dark; begins when lights are turned off

38
Q

Dark Adaptation

- Visual Pigment Regeneration

A

= in weak light, there are lots of pigments available; therefore, rods and cones absorb and respond to them as much as they can

39
Q

Neural Convergence and Perception

A

Convergence = increased sensitivity of the ganglion cells

40
Q

Consequences of Convergence

A

rods have higher convergence than cones

  • takes less light to generate response from individual rod receptor than from individual cone receptor
  • rod and cone sensitivity is determined by groups of receptors converging onto other neurons
41
Q

Consequences of Lack of Convergence

A

cones have better visual acuity because they have less convergence

42
Q

Visual Illusions

- Lateral Inhibition

A

lateral inhibition: effect in which illumination of receptors ‚inhibits‘ firing of neighboring receptors; increase in contrast and sharpness when it comes to visual response

43
Q

Visual Illusions

- Mach Band

A
  • in dark, small light stimulus enhance rods
  • rods in center of stimulus transduces ‚light‘ signal to brain
  • rods in outside of stimulus transduces ‚dark‘ signal due to lateral inhibition from horizontal cells
  • contrast between light and dark create Mach band effect
44
Q

Visual Illusions

- Hermann Grid

A
  • receptive field at intersection of white cros has more light on inhibitory surround than the one between two black squares
    • excitatory center of this receptive field between squares has stronger response than the other one
    • receptive fields in central fovea are smaller than in rest of retina
  • we do not see a dark area when we look directly at intersection of white cros, but we see it in our peripheral vision

Perception (9 decks)

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