Double Dissociation

Question 1

functional modularity

Answer 1

the assumption that some areas of the brain may specialize to perform high level functions

Question 2

can we associate a (computational level) behavior or function with a

Answer 2

specific (implementational) level portion of the brain?

Question 3

if a single injury causes the loss of both abilities, we might conclude that…

Answer 3

…the abilities are related and the same brain mechanism seems associated with BOTH abilities

= no dissociations

Question 4

if an injury causes the loss of ONLY ONE function, while another function is retained, perhaps …

Answer 4

…different areas of the brain implement those two functions

Question 5

single dissociation

Answer 5

a brain region seems associated with only one ability and dissociated from another

Question 6

the ambiguity with a single dissociation

Answer 6

we know that the damaged brain region was important for one function (the lost or impaired function). However, we don’t know if other brain regions may also be important
for that function.

Question 7

to show functional independence of two brain regions (the what and the where/how pathways) we need to show….

Answer 7

A DOUBLE DISSOCIATION

Question 8

double dissociations

Answer 8

two functions/abilities involve different brain regions

Question 9

double dissociation example

Answer 9

alice has temporal lobe damage (ventral stream): can’t name objects but can determine objects’ locations = single dissociation: of object location processing is not dependent on temporal lobe

Bert has parietal lobe damage (dorsal stream): he can name objects but can’t determine their locations in space = single dissociation: of object recognition not dependent on dorsal stream

conclusion of the combination of the two cases: the behavioral functions (naming objects, determining object’s locations in space) seem to be dependent upon different brain regions

only one organizational structure fits this data:

• loss of ventral stream = loss object naming (recognition)
• loss of dorsal stream = loss of object location

Question 10

ablation studies with monkies

Answer 10

strong instances of double dissociation

1) animal trained on some task = baseline for perceptual capacities and ability to perform that task
2) a specific part of the brain was removed or destroyed (ablated)
3) animal was retrained to determine how much of the perceptual abilities remained or could be regained.
4) the results revealed which portions of the brain were responsible for specific behaviors = if the ablated area was responsible for a certain task or perceptual ability then they wouldn’t be able to relearn or complete that task

Question 11

object discrimination problem

Answer 11

monkies had part of the inferior temporal lobe removed and afterwards could no longer be trained on target identification tasks

Question 12

landmark discrimination problem

Answer 12

part of the parietal lobe was removed: the monkey couldn’t be retrained to use spatial relationships but the monkey could still identify the landmark

stronger double dissociation because they could control exactly where the damage was