L11 - Visual Processing of Objects: cortical organisation

Question 1

Where are the two visual streams?

Answer 1

• Dorsal
  
  • From primary visual cortex (v1) to posterior parietal lobe (occipito-parietal)
• Ventral
  
  • From primary visual (V1) to inferior temporal cortex (occipito-temporal)

Question 2

What does the dorsal stream visual stream do?

Answer 2

• “where” - Ungerleider & Mishkin (1982)
  
  • Computes spatial location
• “how” - Goodale & Milner (1992)
  
  • Uses vision to guide action
  • Strong interactions with motor system
  • PPT couldn’t reach accurately but could state orientation

Question 3

What does the ventral stream do?

Answer 3

• “what” - Ungerleider & Mishkin
  
  • Computes shapes and object identity (both theories agree)
• “action”
  
  • Contributes to conscious perception and awareness (Milner & Goodale)

Question 4

So what are the two theories about the dorsal and ventral stream?

Answer 4

• ‘What’/’Where’ (Ungerleider & Mishkin)
  
  • Functional characterisation in terms of information
• ‘Perception vs Action” (Milner & Goodale)
  
  • Functional characterisation in terms of process (what is vision for?)

Question 5

Are both theories about the dorsal and ventral stream valid?

Answer 5

• Both ideas of the dorsal and ventral stream are correct
• 3 dorsal streams continue beyond posterior parietal cortex
  
  1. Connections to prefrontal cortex, involved in spatial working memory – “where”
  2. Connections to premotor cortex, involved in action – “how”
  3. Connections to medial temporal lobe (hippocampus
     and parahippocampal gyrus), involved in spatial navigation – “where” on an environmental scale
• So dependent on what tasks required, different area will be used