The Visual System 2
- Created by: meg_lou
- Created on: 05-05-17 14:30
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- The Visual System 2
- Structure of the brain
- Visual field
- Area projected onto the retina
- The 2 eyes have slightly different visual fields that overlap
- V1
- At the back of brain
- Information processed in hierarchy
- Processes become more complicated ascending
- Visual field
- Problems
- Eye
- Problems with lens focussing
- Myopia (**) - light focussed in front of retina
- Corrected with a concave lens
- Hypermetropia (LS) - light focussed behind the retina
- Corrected with a convex lens
- Myopia (**) - light focussed in front of retina
- Problems with the retina
- Macular degeneration - losing central vision, usually in aging
- Detereorationof macula on the retina which is responsible for central vision
- Macular degeneration - losing central vision, usually in aging
- Problems with lens focussing
- Brain
- Neurons have a critical period where they obtain specialised function to help in perception
- Dorsal stream is vulnerable here
- Impaired m cell development means the brain cannot correctly determine eye movements
- Could be responsible for several conditions including, ADHD, SZ, depression
- Neurons have a critical period where they obtain specialised function to help in perception
- Eye
- Dorsal and ventral streams
- Dorsal
- From V1 to the dorsal prostrate cortex to posterior parietal cortex
- 'Where' objects are
- Ventral
- From V1 to the ventral prestriate cortex to the inferotemporal cortex
- 'What' objects are
- What vs where theory
- Damage to some areas of cortex may impair some aspects of vision but not others
- Patients with damage to posterior parietal cortex find it difficult to reach for objects but can describe them (affects dorsal)
- Performed poorly because task involved with visually guided movements
- Patients with damage to inferotemporal cortex find it difficult to describe objects but can reach for them (affects ventral)
- Performed poorly because task involved with conscious awareness
- Control of behaviour vs conscious perception theory
- Not about the kinds of information they carry but how they use it
- Dorsal is involved with visually guided movements
- Ventral is involved with conscious perception
- What sets us apart from our ancestors (Goodale)
- Some patients with bilateral lesions to ventral stream cannot consciously see objects but can interact with objects
- DF could scale dimensions of object when she picked it up but couldn't consciously perceive the dimensions
- Some patients with bilateral lesions to dorsal stream can consciously see objects but cannot interact with them
- AT could demonstrate object size with her fingers but could not grasp it
- Could be related to uncomplete separation of M and P cells along parietal and temporal pathways
- Dorsal
- Disorders of visual perception
- Visual agnosia
- Inability to recognise familiar objects
- Occurs after damage to posterior occipital/temporal lobe
- May be able to describe objects but not recognise them
- Apperceptiveagnosia
- Incapable of recognising objects
- Difficult distinguishing between shapes and copying objects
- Incapable of recognising objects
- Associative agnosia
- Unable to assign meanings to objects
- Can draw and copy things
- Could be due to disconnection between language and visual system or problem with semantic processing
- Unable to assign meanings to objects
- Blindsight
- Ability to respond to visual stimulus even with no conscious awareness of it
- Conections could still exist in V1 or they may not pass through scotoma
- Ability to respond to visual stimulus even with no conscious awareness of it
- Hemispatial neglect
- One hemisphere of the brain is damaged - deficit in attention to opposite side
- E.g. only draw one side of objects
- One hemisphere of the brain is damaged - deficit in attention to opposite side
- Visual agnosia
- Structure of the brain
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