Perception

Question 1

Why must sensory information be interpreted?

Answer 1

1. Information is incomplete
2. Too much raw information
3. Must extract what is important or dangerous

-> Our brain must consciously perceive the most important info. in spite of poor quality and vast amount of unnecessary and irrelevant info.

Question 2

Why is there a focus on vision in the study of perception?

Answer 2

1. Large part of our brain is dedicated to vision
2. Seeing is a difficult task and demands interpretation
3. Vision is a good source of environment information

Question 3

What are the 3 misconceptions about visual perception?

Answer 3

1. It is automatic and effortless
2. Provides exact copy of the world
3. Provides rich and continuous visual environment

Question 4

What are the components of visual perception in the brain?

Answer 4

> Eyes (retinas and foveas)
Optic nerves
Optic chiasma
Optic tracts
Lateral geniculate nucleus (LGN - within thalamus)
Visual (primary) cortex (in occipital lobe)

Question 5

What are the light receptor cells and where are they located?

Answer 5

In the retina:

• Rods: low light, not sensitive to colour info. -> black and white
• Cones: well-lit conditions, sensitive to colour info., found in fovea

Question 6

Why is binocular vision only possible for the middle part of the visual field?

Answer 6

Fixating an item so that it is central to visual field make information fall directly onto fovea (contains cones)
-> colour vision occurs only for items we’re directly fixating

Question 7

Why is our mental representation of seeing all surrounding environment not in 3D colour and detail?

Answer 7

Colour vision occurs only for items we’re directly fixating

only middle part of visual field falls directly onto fovea and its containing cones

Question 8

How does the lateral geniculate nucleus direct most of the visual information?

Answer 8

Via optic radiations towards primary visual cortex (= V1, striate cortex)

Question 9

What are the two principles of vision?

Answer 9

1. Vision is hierarchical

2. Vision is modular

Question 10

What makes vision hierarchical?

Answer 10

Brain starts with simple properties (dots and lines), and interprets it into more complex information
- no clear representation of an item in V1

Question 11

What makes vision modular?

Answer 11

Specific parts are dedicated to particular types of information

• if V1 is damaged we become cortically blind
• if V4 is damaged -> colour blindness
• if V5 is damaged -> motion blindness

Question 12

Why do we become cortically blind if the primary visual cortex (V1) is damaged?

Answer 12

It is crucial for fundamental extraction of visual input from incoming information

Question 13

What are the two visual pathways?

Answer 13

1. Dorsal stream
   - ‘where stream’
   - occipital -> parietal cortex
   - V1 - V5
2. Ventral stream
   - ‘what stream’
   - occipital -> temporal cortex
   - V1 - V4

Question 14

What would damage to parts of the ventral stream result in?

Answer 14

‘What stream’

- visual agnosia: failure to recognise objects or even simple shapes

Question 15

How can patients with visual agnosia identify items?

Answer 15

When exploring with their hands

- it’s the combination of basic visual feature with its object-related characteristics that has been lost

Question 16

What would damage to parts of the dorsal stream result in?

Answer 16

Disorders with spatial representational deficits

- primarily affecting the contralateral space of visual field (opposite to injury)

Question 17

How did Haxby (2009) demonstrate the functions of the ventral and dorsal streams?

Answer 17

Neuroimaging:

• activation in dorsal stream for location judgements
• activation in ventral stream for object recognition decisions

Question 18

Why is our visual world not an exact copy of the visual world?

Answer 18

Saccades provide integrated successive fixations across the visual field
-> illusion of stable visual world

Question 19

How did Rensink demonstrate change blindness?

Answer 19

He interleaved an original scene and a changed scene with a blank grey which causes a flicker

• flicker = motion across the whole image as it’s flashing up
• > masks the transient motion associated with the change in image directly

-> moment-to-moment representation of visual field that we possess is not very detailed

Question 20

What is the blind spot present in each of our eyes?

Answer 20

No rods or cones -> no visual input processed

Question 21

Why do we have no perception of constantly missing a small part of the visual field, even though there’s a blind spot in each of our eyes?

Answer 21

Our brain gives us the mental representation of a continuous perception across the whole visual field
-> illusion

Question 22

Why is perception an effortful and intricate process?

Answer 22

> Input from the world contain insufficient information

• > our visual system adapts by computing certain expectations that we have
• it can overcompensate -> illusory images

> We can process little information at any one time

• visual input contain overwhelming sensory info.
• > attention selects relevant parts of visual field

Question 23

What happens when the visual input is ambiguous?

Answer 23

Our visual system gives us a clear interpretation of what we’re seeing

• we can simultaneously perceive multiple possibilities of a single ambiguous image
• our visual system automatically uses context to interpret the visual scene