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Cognitive psychology > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

Light definition

A

Electromagnetic radiation with a specific frequency that falls within the observable spectrum.

  • Wavelength usually expressed in nanometers.
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2
Q

Cornea

A

Light first passes through the cornea.
The cornea protects the structures inside the eye and refracts and bends the light rays.

  • This happens because the cornea tissue is denser than air.
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3
Q

Pupil

A

The pupil is an opening in the iris. It appears to be black because light that enters the eye is absorbed by the retina.

  • The size of the pupil determines how much light enters the eye.
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4
Q

Lens

A

After the light passes through the cornea, it is refracted again by the lens to focus light on the retina.

  • Achieved by ciliary muscles that bend or flatten the lens.
  • 20% of refraction happens in the lens, 80% in the cornea.
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5
Q

Retina

A
  • The inside lining of the eye.
  • Cones and rods: Around 7 million receptors are cones, the other 123 million are rods.
  • Light passes through ganglion cells and bipolar cells before reaching the cones/rods.

The retina comprises 130 million light-sensitive receptors that are responsible for signal transduction.

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6
Q

Cones

A

Mostly packed in the ‘pit’ (fovea) in the central part of the retina (macula).

  • Responsible for perception of colour and fine details (foveal vision if central and sharp).
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7
Q

Rods

A

Mostly centred around the fovea.

  • Sensitive to low intensity light.
  • Colourblind.
  • Responsible for perception of low movement, peripheral vision, night vision.
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8
Q

Blind spot

A

Where the optic nerve leaves the eye.

  • Discovered by anatomist Mariotte.
  • Cephalopods don’t have a blind spot as retinal axons pass over the back of the retina. Our brain fills the blind spot with immediate surroundings.
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9
Q

Hyperopia (hypermetropia)

A

Eye is too short, focal place (where light is focused) lies behind the retina.

  • The person is farsighted and cannot focus on close objects.
  • This is corrected with convex lens+
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10
Q

Myopia

A

Eye is too long, focal plane lies before the retina.

  • The person is nearsighted and sees distant objects as blurred.
  • This is corrected with concave lens-
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11
Q

Presbyopia

A

Type of farsightedness due to hardening/diminished elasticity of the lens as we get older (<40 years),

  • Corrected with reading glasses - convex lens.
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12
Q

Astigmatism

A

Imperfections in the spherical curvature of the cornea of the lens results in multiple focal points (blurry vision at all distances).

  • Can be corrected with a cylinder.
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13
Q

Cataract

A

Clouding of the lens (age, diabetes).

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14
Q

Macular degeneration

A

Retinal degeneration of the fovea, the focus is black and distorted.

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15
Q

Glaucoma + what causes it

A

Worsening/loss of peripheral vision

  • Failure of nerve cells due to increased eye pressure.
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16
Q

Receptive fields of ganglion cells (also how light passes through the eye)

A

Compressed information from cones/rods are sent via bipolar cells to ganglion cells, that relays the information to the optic nerve.

  • One ganglion cell receives input from multiple cones/rods.
  • Donut like - On centre v. Off centre cells.
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17
Q

On-centre cells

A

They are neurons with receptive fields that are primarily activated by a stimulus presented in the central region of their receptive field (donut hole)

  • Can offer an explanation for some visual illusions like Hermann grid.
18
Q

Hermann grid + receptive field

A

The white bands are equally intense throughout, but gray circles appear at their intersections.

  • Receptive field 1 receives more surround inhibition than 2.
    Meaning more on light surround = more inhibition = firing at slower rate than 2 –> 1 is perceived less intense than 2.
19
Q

Mach bands + receptive field

A

The luminance is the same within one band, but perceived luminance within the band varies. The contrast is exaggerated on the edges.

  • Receptive field 2 receives more surrounding inhibition than 1. Meaning more light on surround = more inhibition = firing at slower rate than 1 –> 2 perceived as less intense than 1.
20
Q

Visual pathway explained

A

The ganglion cells feed forward information to V1. The nasal part of the optic nerve crosses at the optic chiasm(a), the temporal part continues to the ipsilater (same) side. This results in the projection of the left visual field in the right hemisphere.

21
Q

Lateral geniculate nucleus in the visual pathway

A

The vast majority of the nerve fibres in the optic tract project to the LGN in the dorsal part of the thalamus.

  • LGN is the main relay station in the pathway to the primary visual cortex.
22
Q

Optic nerve is damaged/severed

A

All vision is lost in that eye.

23
Q

Optic chaism(a) is damaged/severed

A

Outer part of the visual field is lost in both eyes.

24
Q

Visual pathway from LGN to V1 is damaged/severed

A

Visual field is lost in both eyes.

25
Q

Off-centre cells (firing rate)

A

Neurons that decrease their firing rate when a stimulus is presented in the central region of their receptive field. These cells are primarily sensitive to the absence of stimulation in their central region.

26
Q

LGN - layered (cells in V1)

A
  • 100m cells in V1 have retinotopic organisation and there is cortical magnification.
  • Cells in V1 selectively respond to lines with particular orientation within specific retinal location.
27
Q

2 main routes for visual paths

A
  1. Ventral pathway
  2. Dorsal pathway
28
Q

Ventral pathway

A

Pathway to temporal cortex: WHAT (shape identity of object).

29
Q

Dorsal pathway
(what do those areas do?)

A

Pathway to parietal areas (perceiving spatial relations, aiming, reading).

  • Originally viewed as WHERE but is now viewed as HOW.
30
Q

3 properties of colour perception

A
  1. Hue (which colour? Wavelength).
  2. Saturation (complexity of light. Range of different wavelengths).
  3. Brightness/intensity (wave amplitude).
31
Q

Additive mixing

A

Red, green, and blue light can be combined (wavelengths are added in the mix).

32
Q

Trichromatic theory (Young-Helmholtz)

A

All colours can be obtained by mixing red-green-blue in different proportions.

33
Q

3 types of cones in the eye.

A
  • Small, medium, large
34
Q

Small (s) cones

A
  • ~2% of cones in retina
  • Respond most to blue spectrum
  • Peak ~420 nm = violet.
35
Q

Medium (m) cones

A
  • ~33% of cones in retina.
  • Respond most to green-yellow spectrum.
  • Peak ~530 nm = yellowish green.
36
Q

Large (l) cones

A
  • Majority of cones in retina.
  • Response most to red spectrum.
  • Peak at ~560 nm = yellow.
37
Q

Subtractive mixing

A

Mixing coloured ink, paint, etc.

  • Wavelengths are removed in the mix.
  • Primary colours are subtractive as they cannot be mixed from anything.
  • Cyan, magenta, yellow, key [black]: colour coding model based on subtractive mixing.
38
Q

How colours are distinguished in the retina

A

Most parvocellular (small) ganglion cells are sensitive to difference in wavelengths that is reflected in their receptive fields.

39
Q

Opponent-process theory

A

Six primary colours organised into 3 pairs (red-green, blue-yellow, black-white).
The opponents inhibit each other on ganglion-level, which leads to perceptive achromatic (colourless) light.

  • Explains red/green colourblindness.
  • Goes against trichromatric theory
40
Q

Why can’t I see colours at night?

A

Cones need light with high intensity. At night, only rods are used (rods are colourblind).
Since the fovea is packed with cones, fixating next to an object at night (rather than fixating directly on the object) makes it clearer

41
Q

What does it mean that my eyes ‘have to adapt to the dark’?

A

After photons hit rods, the cells need to recover (rods saturate more easily than cones), which can take about half an hour (when going from the bright sunlight to complete darkness). But, after that, rods become very sensitive.

  • About 9 photons are required at the receptor level to detect a light source
  • These photons are spread over many rods, so a rod must be capable of detecting a single photon

Cognitive psychology (13 decks)

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