Mechanisms of perception, conscious awareness and Attention

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V1 Physiology

  • 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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Hierarchical Organisation

  • 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

Evidence

  • 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.

Blindsight

  • 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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Functional Segregation

  • 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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Double disassociation

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.

Double disassociation

  • 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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