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Perception > Light and the eye > Flashcards

Light and the eye Flashcards

1
Q

What is visible light?

A

Visible light is a specific band of energy within the electromagnetic spectrum.

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2
Q

How is electromagnetic energy measured?

A

Distance between the peaks of each electromagnetic wave. Measured un meters and nanometers.

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3
Q

What is one nanometer?

A

10(-9) or 0.000000001 meter. (One billionth of a metre)

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4
Q

What does the visible light spectrum for humans range from?

A

400 to 700 nanometers.

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5
Q

What happens when there is a aperture in a wall?

A

The image will appear inverted on the other side.

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6
Q

What happens when the size of an aperture increases?

A

The image quality decreases.

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7
Q

Why are lenses better than apertures?

A

Because they bend incoming light rays to ensure sharp and bright images.

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8
Q

What is the cornea?

A

The transparent tissue at the very front of the eye.

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9
Q

What is the sclera?

A

Tough white tissue that coats the rest of the eye.

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10
Q

What is the iris?

A

Muscle tissue that controls the size of the pupil and thereby, the amount of light that enters the eye.

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11
Q

What do the cornea and the lens form?

A

An inverted image on the retina at the back of the eye.

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12
Q

How much of focusing does the cornea account for?

A

80%

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13
Q

What does the lens do?

A

Adjusts its shape according to the viewed object distance, accounts for the other 20% of focusing.

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14
Q

What is accomodation?

A

Occurs when the ciliary muscles tighten which causes the lens to thicken and focus on objects closer.

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15
Q

What is myopia?

A

Near sightedness, the inability to see far objects clearly.

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16
Q

What is refractive myopia?

A

cornea or lens bends too much light.

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17
Q

What is axial myopia?

A

Eyeball is too long.

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18
Q

How is myopia corrected?

A

Concave lens.

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19
Q

What is the near point?

A

The distance where the lens can no longer adjust for close objects.

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20
Q

What is prebyopia?

A

The process of gradually losing the ability to focus on near objects due to age.

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21
Q

Why does presbyopia occur?

A

Hardening of the lens and weakening of the ciliary muscles, corrective lens are needed for close activities, such as reading.

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22
Q

What is hyperopia?

A

Inability to see nearby objects clearly.

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23
Q

Why does hyperopia occur?

A

Usually eyeball is too short or focus point is behind retina.

24
Q

What do the outer segments of photoreceptors contain?

A

Light sensitive visual pigment, light is transduced into electricity.

25
Q

What happens to the electrical signal in the photoreceptors?

A

It is propagated from synaptic terminal via a set of neurons to the brain.

26
Q

What are the two components of the visual pigment molecules on photoreceptors?

A
  • Opsin: large protein.

- Retinal: a light sensitive molecule.

27
Q

When does visual transduction occur?

A

When the retinal absorbs light.

28
Q

What is isomerization?

A

When the retinal changes its shape after absorbing light.

29
Q

Where does the transduction of light to electricity take place?

A

In every photoreceptor, including rod and cone cells.

30
Q

What is fovea?

A

The place on the retina that has the highest visual acuity.

31
Q

How many rod and cone cells does a person haave?

A

120 million rods and 5 million cone.

32
Q

What is the blind spot?

A

The place where the optic nerve leaves the eye.

33
Q

Why don’t we see the blind spot?

A

Because one eye covers the blind spot of the other, it is located away from the centre of the visual field, the brain fills in the spot.

34
Q

How are cone cells spaced?

A

Small and numerous in the fovea, few in periphery .

35
Q

What time of vision do cone cells do?

A

Colour and day time spatial vision.

36
Q

What are the shape differences between rod and cone cells?

A
  • Rod: Large and cylindrical

- Cone: Small and tapered

37
Q

How are rod and cone cells distributed on the retina?

A

Fovea consists solely of cone cells, peripheral has both rod and cones but more rod than comes.

38
Q

What was the basic method used to test for dark adaptation curve in both rod and cone cells?

A

Observer is light adapted, light is turned off, observer adjusts the intensity of a test light until they can just see it. (the detection thresholds) threshold values are recorded at different times after the light was turned off.

39
Q

How does sensitivity split into stages in the dark adaptation experiment?

A

Sensitivity increases in two stages.

  • Stage 1 takes place for 3-4 minutes.
  • Then sensitivity levels off for 7-10 minutes, rod cone break
  • Stage 2 shows increased sensitivity for another 20-30 minutes.
40
Q

How large is the sensitivity of the rod cells after the dark adaptation?

A

100,000 times greater.

41
Q

What important role does the rod system serve?

A

It extends the range of illumination over which we can operate, an evolutionary advantage.

42
Q

What are bipolar cells?

A

They have two poles and convey information from one nerve to another.

43
Q

What are ganglion cells?

A

They pass information to optic nerve fibres in the eye from the bipolar cells.

44
Q

How many rod cells converge to one ganglion cell?

A

120

45
Q

How many cone cells converge to one ganglion cell?

A

6

46
Q

How many cone cells converge to one ganglion cell in the fovea?

A

It is one to one.

47
Q

What is the advantage of having a one to one connection between photoreceptor and ganglion or bipolar cell?

A

It gives maximal spatial resolution.

48
Q

What is gained from many rod or cone cell connections to a bipolar cell?

A

Spatial summation and an increased sensitivity to light.

However at the expense of spatial resolution.

49
Q

What is spatial summation?

A

When the stimuli is activated from multiple different rod or cone cells at once causing the threshold to be met.

50
Q

Why is summation at the cost of resolution?

A

Because the more information combined the less detailed information is held as a lot of information is being converged.

51
Q

What are the pros of rod cells being more sensitive to light than cones?

A

They take less light to respond, they have a greater convergence which leads to more summation as there is more rods being inputted to one ganglion or bipolar cell increasing the liklihood of response.

52
Q

What are the cons of rod cells being more sensitive to light?

A

The rod pathway to the brain cannot resolve detail and resolution as well as cone pathway.

53
Q

What are the pros of cone cells having one on one connections?

A

They produce higher visual acuity.

54
Q

What are the cons of cone cells having one to one connections?

A

They require more light to respond than rod cells.

55
Q

What is the spatial resolution in the fovea?

A

150,000 cones/mm squared

Perception (11 decks)

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