COGS101 Lecture Notes - Lecture 6: Fusiform Face Area, Agnosia, Extrastriate Cortex
2 Jun 2018
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Agnosia – Week 6
What are Agnosias?
• Means ‘absence of knowledge’
• Can be absence of knowledge of faces etc.
• Different modalities of vision, hearing, smell, taste etc.
• Can be acquired (brain injury/trauma) or developmental (lifespan)
• Cannot recognize things from vision (it is not a memory or semantic problem)
What are object perception and agnosia?
• A disorder in object perception
• OP allows us to interact with the world
• Why is object perception interesting?
o Computers do not get close to what our brains do
o We do not know how our brains do it
o What we see is not what we see
o Our brains generate a percept based on input and prior experience
• Top-down influences on object perception (picture of dog and mess)
• Three-stage model of object perception:
o Local features
o Shape representation
o Object representation
• Agnosia:
o Damage to extra-striate cortex
o Complete visual fields
o Normal colour, depth and movement
o Disordered object perception
Different Types of Agnosia in Different Sensory Systems:
• Apperceptive agnosia
o Still normal acuity, brightness discrimination, colour vision, depth and
contour perception
o Unable to:
▪ Group elements
▪ Recognise or match objects
• Simultanagnosia
o Dorsal form
▪ Able to recognize elements but not the whole scene
▪ One object at a time
▪ Gaze, pointing and reaching problems
o Ventral form
▪ Multiple objects can be seen, manipulated, counted etc.
▪ Cannot grasp the meaning of the whole scene
• Associative agnosia
o Meaning of an object is affected (not anomia)
o Confabulation (guessing) often occurs
o Listing of distinct features
▪ Glove as a container with five pouches
• Optic aphasia
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