Lecture 11 - Object Recognition Flashcards
pathways that transmit and process visual information
to produce basic features
Ganglion axon pathway • Visual thalamus – lateral geniculate nucleus (LGN) • Striate cortex (V1) • Hierarchical organization • Feature detectors
basic palette to start creating objects
how do we find the objects?
visual form agnosia
brain damage: visual form agnosia: can’t recognize objects as a certain kind of thing
inferior temporal lobe
On the basis of stroke patients with visual agnosia, it was known that this area was involved with OBJECT RECOGNITION
called the “What pathway” because it was critical for target identification tasks.
stroke patients with parietal lobe damage
problems dealing with spatial relationships (being able to understand where things are in relation to other thing)
difficulty using landmarks: “‘where is the door?’ ‘it’s near the exit sign’”
can’t reference an object in the environment and then infer something from it and how they could use it, even though they could recognize it
difficulty with spatial relationships and remembering
landmarks.
Ungerleider & Mishkin (1982) tested functional separation in monkeys with ablation studies.
- First, an animal was trained on some task to indicate their perceptual capacities and then measure their ability to do that task
- Second, after training, a specific part of the brain was removed or destroyed (ablated).
- Third, the animal was retrained and measure their ability to see how much they can get back and to determine which perceptual abilities remain.
comparison: how much of the ability could be recovered? If almost all of it could be recovered then you can infer then that area of the brain wasn’t strongly related to that function
• The results reveal which portions of the brain were responsible for specific behaviors.
Object discrimination problem
– Monkey was shown an object and rewarded (with food) for recognizing it as a target.
– Removal of inferior temporal lobe tissue
resulted in problems with the object discrimination task = determined the IT is “What pathway”
because it was critical for target identification tasks.
Landmark discrimination problem
– Monkey was trained to pick the food well
next to a cylinder.
– Removal of parietal lobe tissue resulted in
problems with the landmark discrimination task = determined this area was called the “Where pathway” as it was necessary for using landmarks and spatial relationships.
parietal lobe
“where/how pathway”
How do we isolate visual processing streams in people?
go out and find large populations: what deficits are associate with which type of brain damage = See if people, as a result of brain injury or illness, tend to lose
specific functions while retaining others. [Natural experiments, because you’re not inducing anything]
looking for a dissociation
Dissociation
loss of both?
loss of one?
One function is absent while another is present.
- For example, if a person loses the ability to name objects, do they also lose the ability to determine their locations?
- If a single injury causes the loss of both abilities, we might conclude that the abilities are related and the same brain mechanism seems associated with both abilities.
- However, if an injury causes the loss of one only one function, perhaps different areas of the brain implement those two functions (dissociated).
- In this case, the brain region seems associated with only one ability and is dissociated from the other.
dissociation example
you are able to identify an object but can’t do spatial reasoning with that object
single dissociation
example ?
Two functions/abilities seem to involve different
brain mechanisms.
based on one piece of damage
Alice damage to temporal lobe - can’t name objects BUT SHE CAN determine their locations in space - keeps the where info loses the what info
no dissociation
if Alice lost the temporal lobe and then couldn’t name objects or determine their locations in space
double dissociation
two functions/abilities involve different brain
mechanisms and operate independently (requires two individuals).
you need two different people to show it: show different behaviors
Bert has parietal lobe damage, can name objects find but can’t determine spatial relationships = this damage is associated with a different kind of error
Alice can do one task that Bert can’t and has different damage and vice versa
same area doesn’t seem to be related to the same functional deficits
a way of getting at which area of the brain is associated with which function
Dissociations can also be shown in individuals with intact brains and abilities (Ganel et al., 2008).
- Visual illusions provide one way of dissociating object visual judgments (perceptual identity information) from action information (‘how’ an object is used).
- Line 2 appears longer than line 1; however, this is a perceptual illusion => converging lines give an illusion of depth => visual identification pathway is telling you based on experience, 2 has got to be bigger cause i’ve seen 100000 things like that
