1. Object vision and spatial vision: two cortical pathways
Mishkin, Ungerleider & Macko (1983)
Presented by Joel Tan

2. Question
What is the functional organization of the extrastriate cortex?
More specifically: Are there separate streams for processing object information / location information?

3. Alternatives (1)
Visual functions are exclusively in striate cortex (Lashley)
Extrastriate cortex has visual functions
Solved! Lashley loses

4. Alternatives (2) Extrastriate cortex has unified visual functions
Extrastriate cortex is divided in functionally and anatomically separate “streams”
Solved! There are streams

5. Ungerleider & Mishkin (80s)
Alternatives (3)
There is a tectofugal stream that guides action and a geniculostriate stream that guides perception. (Evidence from birds)
There is a dorsal stream for space perception and a ventral stream for object perception (Evidence from non-human primates)
There is a dorsal stream that guides action and a ventral stream that guides perception (Evidence from humans)
Pohl & Schneider (70s)
Ungerleider & Mishkin (80s)
Goodale & Milner (90s)

6. Logic Lesioning: The method of double dissociation.
Double dissociation “establishes” the correspondence between a particular function and a brain region. (1:1)
Example: Lesioning Area A impairs function C but not function D. Conversely, lesioning Area B impairs function D but not C. Hence, we associate A with C and B with D.

7. Method
Compiling a large database of lesioning studies in rhesus monkeys, using the method of double dissociation.

8. Results – Ventral for Objects
Lesioning the ventral stream led to deficits in object discrimination but not object localization.

9. Results – Dorsal for Space
Lesioning the dorsal stream led to deficits in landmark discrimination but not object recognition.

10. Interpretation
In primates, extrastriate cortex consists of two anatomically and functionally separate streams!

11. Interpretation Dorsal stream: Spatial vision
Ventral stream: Object vision

12. Interpretation – arising issues
Integration:
If the two functions are separate, how does the brain recombine them into a coherent percept?
This is called the “binding” problem.
Particularly tricky if there is more than one object in visual world (as usual)
Is this the function of consciousness?

13. Problems Species: How do the results generalize
Alternatives: Doesn’t rule out perception for action vs. perception hypothesis.
Lesioning is not a bulletproof method: Often unspecific and unprecise, the problem of diaschisis, unaccounted for side-effects.