Perception Flashcards
Why must sensory information be interpreted?
- Information is incomplete
- Too much raw information
- 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.
Why is there a focus on vision in the study of perception?
- Large part of our brain is dedicated to vision
- Seeing is a difficult task and demands interpretation
- Vision is a good source of environment information
What are the 3 misconceptions about visual perception?
- It is automatic and effortless
- Provides exact copy of the world
- Provides rich and continuous visual environment
What are the components of visual perception in the brain?
> Eyes (retinas and foveas)
Optic nerves
Optic chiasma
Optic tracts
Lateral geniculate nucleus (LGN - within thalamus)
Visual (primary) cortex (in occipital lobe)
What are the light receptor cells and where are they located?
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
Why is binocular vision only possible for the middle part of the visual field?
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
Why is our mental representation of seeing all surrounding environment not in 3D colour and detail?
Colour vision occurs only for items we’re directly fixating
only middle part of visual field falls directly onto fovea and its containing cones
How does the lateral geniculate nucleus direct most of the visual information?
Via optic radiations towards primary visual cortex (= V1, striate cortex)
What are the two principles of vision?
- Vision is hierarchical
2. Vision is modular
What makes vision hierarchical?
Brain starts with simple properties (dots and lines), and interprets it into more complex information
- no clear representation of an item in V1
What makes vision modular?
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
Why do we become cortically blind if the primary visual cortex (V1) is damaged?
It is crucial for fundamental extraction of visual input from incoming information
What are the two visual pathways?
- Dorsal stream
- ‘where stream’
- occipital -> parietal cortex
- V1 - V5 - Ventral stream
- ‘what stream’
- occipital -> temporal cortex
- V1 - V4
What would damage to parts of the ventral stream result in?
‘What stream’
- visual agnosia: failure to recognise objects or even simple shapes
How can patients with visual agnosia identify items?
When exploring with their hands
- it’s the combination of basic visual feature with its object-related characteristics that has been lost
What would damage to parts of the dorsal stream result in?
Disorders with spatial representational deficits
- primarily affecting the contralateral space of visual field (opposite to injury)
How did Haxby (2009) demonstrate the functions of the ventral and dorsal streams?
Neuroimaging:
- activation in dorsal stream for location judgements
- activation in ventral stream for object recognition decisions
Why is our visual world not an exact copy of the visual world?
Saccades provide integrated successive fixations across the visual field
-> illusion of stable visual world
How did Rensink demonstrate change blindness?
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
What is the blind spot present in each of our eyes?
No rods or cones -> no visual input processed
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?
Our brain gives us the mental representation of a continuous perception across the whole visual field
-> illusion
Why is perception an effortful and intricate process?
> 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
What happens when the visual input is ambiguous?
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
