Week 6 - Cortical pathways for vision & Perception Flashcards
What is Agnosia?
Inability to recognise objects. Ability to recognise shape, motion perception are intact. However, these can’t be put together to understand what the object is as a whole. Just perceiving its parts is NOT ENOUGH
What are the two cortical pathways for vision?
Dorsal stream & ventral pathway
Dorsal stream = V1 (occipital) to posterior parietal cortex. Important for object location (where). Concerned about where the object is located in space, not so much what it is.
Ventral stream = occipital –> temporal lob. Important for object perception. Thus, you can lose the ability to recognise an object if there is damage (agnosia)
Explain severe Agnosia
Dorsal stream is intact, however not the ventral stream.
Task 1 - could put card into slot machine (using visual info in a different way to guide action. Main concern is location information).
Task 2 - couldn’t match the angle of the slot (because you firstly have to recognise the object to do this. Therefore when you have to look at something and verbally report its property, you need ventral neurons.
What is Optic Ataxia?
Opposite of Agnosia.
Damage in the dorsal stream
Intact object recognition, however inability to use visual info to guide action
Lesions in the Parietal Cortex
Face perception. What does it require?
Face perception requires holistic processing; when you look at two faces side by side, you can tell they are different immediately.
Perception of whole object goes beyond just perceiving its elements.
E.g. shown picture of Larry & Larry’s House (whole condition. Next: shown Larry’s nose & a door - is this Larry’s door or not? (part condition)
Whole object condition = higher accuracy % correct. Part object condition = lower accuracy % correct.
Suggests that in our neurological brain we are still perceiving objects holistically. So what we can learn from agnosia is that there is something else going on holistically.
