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Perception and Attention > Low-level visual processing > Flashcards

Low-level visual processing Flashcards

1
Q

What is ‘accommodation’?

A

The adjustment of the lens to focus light on the retina.

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2
Q

What percentage of the brain comprises the visual cortex?

A

20%

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3
Q

How many steps are there before visual stimuli reach the visual cortex?

A

3

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4
Q

Which steps have to occur before visual stimuli reach the visual cortex?

A
  • Reception: absorption of physical energy by receptors in the eye.
  • Transduction: the conversion of physical energy to electrochemical patterns in the neurons.
  • Coding: One to one mapping between the physical stimulus and neural activity. One ‘block’ of light is dealt with by one neuron.
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5
Q

What are cone cells responsible for in the eye?

A
  • colour vision

- visual acuity

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6
Q

What are rod cells responsible for in the eye?

A
  • vision in low light

- movement

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7
Q

Which types of receptors are more numerous in the eye?

A

Rod cells.

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8
Q

What are the two (important) visual pathways?

A

Parvocellular and magnocellular.

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9
Q

What does the parvocellular pathway involve?

A
  • Input comes from cone cells

- Deals with colour and fine detail

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10
Q

What does the magnocellular pathway involve?

A
  • Input comes from rod cells

- Movement/motion

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11
Q

Describe the 5 components of the pathway from the eye to the brain.

A
  • Retina
  • Optic nerve
  • Optic chiasma
  • Lateral geniculate nucleus
  • Cortical area V1
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12
Q

What is the retina?

A

A layer of light sensitive cells at the back of the eye.

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13
Q

What is the optic nerve?

A

A pair of nerves which transmit impulses from the retina to the brain.

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14
Q

What is the optic chiasm?

A

The location at which the optic nerve crosses over.

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15
Q

What is the lateral geniculate nucleus?

A

Two bodies in the thalamus where the optic nerve terminates.

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16
Q

What is the receptive field?

A

The region of sensory space in which light will trigger the firing of that relevant neuron.

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17
Q

What is lateral inhibition?

A

A reduction in the activity of one neuron caused by activity in a neighbouring neuron.

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18
Q

What is the center-surround receptive field?

A

Specific neurons are linked to specific patterns of light in a receptive field. (e.g dark middle or light outside)

19
Q

What is retinotopic organisation?

A

The arrangement of neurons being directly linked to the section of the visual field that they respond to.

20
Q

What is V1 responsible for?

A

Basic information from the visual field, such as edges, orientations and wavelengths of light.

21
Q

Several LGN cells combine to form…

A

Simple cells

22
Q

Several simple cells combine to form…

A

Complex cells.

23
Q

What is cortical blindness?

A

A condition which is diagnosed when patients cannot consciously report objects presented in a region of space. Caused by damage to V1.

24
Q

What is the ‘what’ pathway involved in?

A

Colour and form processing. Temporal/ventral.

25
Q

What is the ‘where’ pathway involved in?

A

Movement processing. Parietal/dorsal

26
Q

Who devised functional specialisation theory?

A

Zeki (1992, 1993)

27
Q

What does the functional specialisation theory suggest about the visual cortex?

A

That different parts of the visual cortex are specialised for different functions.

28
Q

According to functional specialisation theory, what are the roles of each visual area?

A

V1 & V2 - shapes
V3 (V3a) - form & moving objects
V4 - colour
V5 - visual motion

29
Q

What evidence is there for V4 and V5?

A

Zeki (1991) conducted a PET study and found that:

  • V4 was more active for coloured images compared to greyscale images.
  • V5 was more active for moving dots compared with static dots.
30
Q

What evidence is there against V4 being linked to colour?

A

Patients with cortical achromatopsia, who can’t see colours due to V4 damage. However, damage also to V2 and V3.

31
Q

What is the name of the condition that arises when there is damage to visual area V5 (MT)?

A

Akinetopsia.

32
Q

What evidence is there for V5?

A

Patient LM had damage to V5, was good a locating stationary objects, but could not detect motion in objects.

33
Q

What is the synchronisation hypothesis?

A

Form, colour, motion etc is bound together across the different areas.

34
Q

What are the three different aspects of colour?

A
  • Hue
  • Brightness
  • Saturation
35
Q

What is hue?

A

The actual colour category. (red, blue, yellow, etc)

36
Q

What is brightness?

A

The perceived intensity of light

37
Q

What is saturation?

A

The paleness of the colour.

38
Q

What is trichromatic colour theory and who devised it?

A

Hermann von Helmholtz postulated that there must be 3 types of colour receptors in the eye, each responding to different wavelengths of light.

39
Q

What were the three colours and wavelengths that Trichromatic theory proposed?

A
  • Blue (short)
  • Yellow/green (medium)
  • Red (long)
40
Q

What does the opponent-process theory suggest?

A

There are three ‘opponent processes’ - pairs of colours. Suggests that we cannot perceive both colours in an opponent-process at once.

41
Q

Which two studies have investigated the opponent-process theory?

A

Hering (1878)

DeValois & DeValois (1975)

42
Q

What does the dual-process theory suggest?

A

One achromatic channel combines activity of medium and long-wavelength cones to measure the intensity of the light.

A blue yellow channel measures the difference between medium and long wavelength cone signals

A red-green channel represents the difference between these signals.

43
Q

What is colour constancy?

A

The tendency for a surface or object to appear to have the same colour, despite the fact they have changed slightly.

44
Q

What is chromatic adaptation?

A

The decrease in the sensitivity to light of any given colour over time.

Perception and Attention (10 decks)

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