- Hubel and Wiesel Nobel Prize winners, discovered the functional organisation and physiology of V1.
- Three types of neurons were distinguished: Simple cells, complex cells, and hypercomplex cells.
- V1 neurons transform information - they are orientation selective and direction selective.
- Also found that the V1 is organized in an orderly fashion
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- Specificity and complexity increases with each level - e.g. receptor destruction, total loss of sense. Secondary sensory cortex destruction leads to a specific sensory deficit.
- Sensation - detecting a stimulus.
- Perception - higher order process intergrating, recognizing, interpreating stimulus.
- Damage: Primary visual cortex.
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Damage: Primary Visual Cortex
- Damage to area of PVC - Scotoma.
- How to test: Fixed red dots flash on and off around different areas of visual field, maps the scotomas.
- Unaware - similar to completion fo blind spot to fill in the gaps.
- The ability to respond to a visual stimulus even with no conscious awareness (due to a scotoma).
- May be that some connections still exist in V1, allowing for reactions without awareness.
- May be that this message gets to the brain that do not pass through the scotoma.
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- Each of the three levels of cortex contains functionally distinct areas - i.e. respond to different aspects of the stimuli.
- Magnocelluar pathway, colour in-sensitive in LGN, orientation selectivity in V1, processing visual motion MT.
- Parvocelluar, parvocelluar LGN layers show colour opponency, V1 complex cells processing visual object shape.
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Sensory areas of the cortex
- Secondary - input mainly from primary.
- Association - input from more than one sensory system, usually from secondary sensory cortex.
- Macaque monkeys - 30 different PV areas, 24 secondary areas, 7 association areas all processing visual information.
- Evidence - Akinetopsia
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Object discrimination task/Landmark discrimination task
- Bilateral lesion to the temporal lobe lead to a deficit in object discrimination.
- Bilateral lesion to parietal lobe leads to deficit in location discrimination.
- Damage to the ventral stream - no conscious perception, but can interact with objects (the woman that could grasp objects she did not consciously see).
- Damage to the dorsal stream - can consciously see objects but cannot interact with that - the case of AT, the woman who could not accurately grasp unfamiliar objects that she saw.
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Sensory areas of the cortex 2
- Association - input from more than one sensory system, usually from secondary sensory cortex - most of the cortex surface.
- Responsible for the complex sensory processing.
- Interactions between input (primary sensory systems) and output (generation of behaviour).
- Known as cognition - means the process by which we come to know the world.
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