COGS101 Lecture Notes - Lecture 8: Extrastriate Cortex, Agnosia, Simultanagnosia
18 May 2018
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AGNOSIA
WHAT IS AGNOSIA?
• Absence of knowledge, can come in different forms, objects and places etc;
• Can be acquired or developmental;
• They know, say for example, what a comb is, but they can't recognise it when shown it. Not
a memory or language problem.
WHY IS OBJECT PERCEPTION INTERESTING?
• Computers do not get close to what our brains do;
• We do not know how our brains do it;
• Our brains interpret a percept based on input and prior experience.
INFLUENCES ON OBJECT PERCEPTION
Our own knowledge – our brain generates perceptions.
THREE STAGE MODEL OF OBJECT PERCEPTION
Image -> local features -> shape representation -> object representation
NEUROPSYCHOLOGICAL EVIDENCE
Agnosia:
• Damage to extra-striate cortex
• Complete visual fields
• Normal colour, depth and movement
• Disordered object perception
TWO FORMS OF AGNOSIA
Apperceptive:
• Deficient shape representation
• Stage two
Associative:
• Deficient object representation
• Stage three
DIFFERENT TYPES OF AGNOSIA
AGNOSIA’S
Apperceptive agnosia:
• Failure in recognition that is due to a failure of perception.
• Unable to group elements, recognise or match objects.
Simultanagnosia:
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
What is agnosia: absence of knowledge, can come in different forms, objects and places etc, can be acquired or developmental, they know, say for example, what a comb is, but they can"t recognise it when shown it. Why is object perception interesting: computers do not get close to what our brains do, we do not know how our brains do it, our brains interpret a percept based on input and prior experience. Our own knowledge our brain generates perceptions. Image -> local features -> shape representation -> object representation. Agnosia: damage to extra-striate cortex, complete visual fields, normal colour, depth and movement, disordered object perception. Failure in recognition that is due to a failure of perception: unable to group elements, recognise or match objects. Simultanagnosia: rare inability to perceive more than a single object at a time, can recognise elements but not the whole scene, multiple objects can be seen, manipulated, counted, cannot grasp the meaning of the whole scene.
