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Perception > Problem 2 > Flashcards

Problem 2 Flashcards

1
Q

Cornea

A

transparent

–> most light photons are transmitted through it
(deutsch - Hornhaut )

–> accounts for 80% of the eyes focusing power

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2
Q

Aqueous Humour

A

fluid derived from blood

–> fills the space immediately behind the cornea

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3
Q

Iris

A
  • Gives the eye its distictive color
  • controls the size of the pupil

–> the amount of light that reaches the retina

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4
Q

Pupil

A

A hole in the iris

–> light enters here

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5
Q

Lens

A

Shape of it is controlled by the ciliary muscles

–> enables the changing of focus

–> accounts for 20% of the eyes focusing power

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6
Q

Vitreous Humour

A

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

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7
Q

Retina

A

Is the network of neurons that covers the back of the eye

–> contains rods and cones

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8
Q

Optic Disc / Blind Spot

A

The point where

  1. the arteries + veins that feed the retina, enter the eye
  2. the axons of ganglion cells leave the eye
  3. there are no photoreceptors
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9
Q

Anatomy of rods and cones

A
  1. outer segment –> adjacent to pigment epithelium
  2. inner segment –> cell body
  3. synaptic terminal –> contain connections to horizontal + bipolar cells
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10
Q

Peripheral retina

A

Includes all of the retina outside of the fovea

  • -> contains both rods and cones (S cones)
  • -> used when detecting + localizing stimuli that we aren’t looking at directly

ex.: seeing a moving truck out of the corner of the eye

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11
Q

Opsin

A

Its structure determines which wavelengths of light the pigment molecule absorbs

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12
Q

Rhodopsin

A

Pigment that is found in rods

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13
Q

Ciliary muscles

A

Increase the focusing power of the lens by increasing the lens curvature

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14
Q

Accomodation

A

Change in the lens shape that occurs when the ciliary muscles tighten

–> this increases the curvature of the lens so that it gets thicker

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15
Q

Why is accommodation necessary ?

A

The increased curvature of the lens increases the bending of the light rays, pulling the focus point back to Point A

–> image is not blurred anymore

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16
Q

Near point

A

Distance at which the lens can no longer accommodate to bring close objects into focus

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17
Q

Presbyopia

A

Increasing distance of the near point as one gets older

  • loss of this ability occurs because

a) lens hardens with age
b) ciliary muscles become weaker

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18
Q

Myopia / Nearsightedness

A

Inability to see distant objects clearly

–> myoptic optical system brings parallel light into focus at a point in front of the retina ( result : blurred image)

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19
Q

What are possible causes of Myopia ?

A
  1. Refractive myopia

–> cornea or lens bend the light too much

  1. Axial myopia

–> eyeball is too long

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20
Q

What are solutions for Myopia ?

A
  1. Moving objects closer
  2. Corrective glasses
  3. Surgical procedure
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21
Q

Far point

A

Distance at which light becomes focused on the retina

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22
Q

Hyperopia / Farsightedness

A

Inability to see near objects clearly

–> focus point for parallel rays of light is located behind the retina

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23
Q

What is the cause of Hyperopia ?

A

Too short eyeball

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24
Q

Solution for Hyperopia ?

A

Corrective glasses

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25
Q

Functions of Visual pigments

A
  1. Trigger electrical signals

2. Determine our ability to see dim light + light in different parts of the visual system

26
Q

What are the components of a visual pigment ?

A

Opsin –> long protein

Retinal –> small, light sensitive component

27
Q

Isomerization

A

Describes the retinals change of shape when the visual pigment molecule absorbs one photon of light

28
Q

Dark adaptation

A

The process of increasing sensitivity in the dark

–> rod and cone receptors adapt to the dark at different rates

29
Q

Fovea

A

small area on the retina, contains only cones

–> image falls on fovea when we look directly at an object

–> specialized for seeing fine details

(M + L cones)

30
Q

Macular degeneration

A

condition that destroys the fovea and a small area surrounding it

–> results in a blind region in central vision

31
Q

Why is the blind spot hard to detect ?

A

a) Mechanisms in the brain fill in the space where the image disappears
b) it is located off to the side of the visual field

32
Q

Process of dark adaptation in steps

A
  1. Sensitivity of cones + rods begins to increase

–> we still see with our cones cause they are much more sensitive

  1. After 3-5 min the cones have reached their maximum sensitivity, while rods are still adapting
  2. ROD CONE BREAK: after 7 min rods become more sensitive than the cones
  3. After 20-30 min rods reach their maximum sensitivity
33
Q

Visual pigment bleaching

A

Process whereby the molecule becomes lighter in color, after the retinal separates from the opsin after isomerization

–> when pigments are bleached, they are no longer useful for vision

34
Q

Visual pigment regeneration

A

Process of reforming the visual pigment so hat it can change light energy into electrical energy

–> retinal returns to its bent shape + becomes reattached to the opsin

35
Q

What are two important connections between perception and physiology ?

A
  1. Our sensitivity depends on the concentration of the visual pigment
  2. The speed at which our sensitivity increases in the dark depends in the regeneration of the visual pigment
36
Q

Pigment Epithelium

A

Layer that contains enzymes that are necessary for pigment regeneration

37
Q

Detached Retina

A

Condition where the retina becomes detached from the pigment epithelium

–> bleached pigments can no longer be recombined, which results in blindness

38
Q

How are the electrical signals transmitted ?

A
  1. Receptors transmit signals to the retina
  2. Signals are then transmitted through the optic nerve to the LGN
  3. Then to the visual receiving area of the cortex
39
Q

Convergence

A

A number of neurons synapse onto a single neuron

–> Signals form rods converge more than those from cones

=> High convergence leads to high sensitivity + poor acuity and vice versa

e.g.: 120 rods –> 1 GC ; 6 cones –> 1 GC

40
Q

Rods

A

Photoreceptor of the eye

–> result in better sensitivity in the dark

—> in general there are more rods than cones in the eye

41
Q

Cones

A

Photoreceptor of the eye

–> result in better detail vision

–> there are 3 types of cone receptors, each having a different sensitivity to the wavelengths of light

–> operate at brighter levels than rods

42
Q

Why are rods more sensitive than cones ?

A
  1. It takes less light to generate a response from an individual rod receptor
  2. Rods have grater convergence

–> rods ganglion cells fire at a lower intensity than cones due to their greater convergence

43
Q

Visual Acuity

A

Refers to the ability to see details

–> cones have better acuity because they have less convergence

44
Q

Receptive field

A

The retinal region over which a cell in the visual system can be influenced (excited or inhibited) by light

45
Q

Center surround organization

A

The area in the center of the receptive field responds differently to light than the area in the surround of the RF

–> excitatory center - inhibitory surround RF vs.
Inhibitory center - excitatory surround RF

46
Q

Center surround agonism

A

When the spot of light becomes large enough to cover the inhibitory area, this stimulation counteracts the centers excitatory response

–> decrease in the neurons firing rate

–> neurons will respond best to spots of light that have the size of the excitatory center

47
Q

Process of turning light energy into electrical energy

A
  1. PHOTOACTIVATION:

Photon enters the outer segment of the photoreceptor + is absorbed by a molecule of the visual pigment

–> photon transfers its energy to the retinal

  1. ISOMERIZATION
  2. REGENERATION
  3. ENZYME CASCADE
    - -> Sequence of reactions that results in transduction
  4. HYPERPOLARIZATION:

Ca+ channels close which causes a decrease in glutamate concentration

–> this signals the bipolar cell that the rod has captured a photon

48
Q

Horizontal cells

A

Retinal cell that contacts photoreceptors + bipolar cells

49
Q

Amacrine cells

A

Retinal cell that contacts

  • bipolar cells
  • ganglion cells
  • other amacrine cells
50
Q

On Bipolar cell

A

Responds to an increase in light captured by the cone

51
Q

Off bipolar cell

A

Responds to a decrease in light captured by the cone

52
Q

Role of on and off bipolar cells ?

A
  • provide information about whether retinal illumination increased or decreased

–> each foveal cone contacts both

53
Q

Bipolar cell

A

Retinal cell that synapses with

  • -> photoreceptors
  • -> horizontal cells

=> it then passes the signals on to ganglion cells

54
Q

Ganglion cell

A

Retinal cell that receives signals from photoreceptors via bipolar + amacrine cells

–> Transit information to the brain + midbrain

55
Q

P Ganglion Cell

A

Receives excitatory input from single midget bipolar cells

–> feed the parvocellular (small/petit) layer of the LGN

56
Q

M Ganglion cell

A

Receives excitatory input form diffuse bipolar cells

–> feed the magnocellular (large) layer of the LGN

57
Q

Characteristics of photoreceptors

A

Info is passed unto bipolar cells via graded potentials

–> electrical potential that varies continuously in amplitude

–> do not respond in an all-or-nothing fashion

58
Q

Why do cones have better visual acuity than rods ?

A
  1. Because they have less convergence

2. It takes more units of light to generate a response from individual cone receptors

59
Q

Lateral inhibition

A

Refers to an effect in which illumination of receptors ‘inhibits’ the firing of neighboring receptors

–> if you illuminate a single receptor (A) you will get a large response; however, when you add illumination to A’s neighbors, the response in A decreases

60
Q

Mach Band

A

Refers to an optical illusion that exaggerates the contrast between edges of the slightly differing shades of gray, as soon as they contact one another, by triggering edge-detection in the human visual system

61
Q

Hermann grid

A

Refers to an optical illusion where you see dark patches appear in the “street crossings”, except the ones which you are directly looking at

Perception (9 decks)

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