Neuroscience of object and face perception Flashcards
How is object recognition rooted in fundamental aspects of cognition?
o Memory
o Decision-making
o Actions and so forth
Where is the visual centre of the brain?
- The visual centre: the back part of the brain
o Occipital lobe
o If you hit the back of your head, you are more likely to ‘see stars’ – visual centre
o However, there is a very large portion of your brain that is linked with vision
What does LOC stand for?
Lateral occipital complex
How is the LOC linked to object recognition?
- Broken into 2 streams
o Lateral and ventral aspects of the occipital lobe - Responds to complex object shapes (e.g., shapes, faces and 3D forms)
o Tend to find, with fMRIs, that this area of the brain responds most to complex objects
o Responds to whole objects, but not scrambled objects
What has been found in patients with LOC damage/lesions?
E.g. patient DF with LOC damage
- Not only was LOC severely damaged, but the remaining areas in the ventral stream showed no more activity
- E.g. if you showed DF a picture of a bed, they would not be able to recognise it
- DF: poor object recognition
- Matching task, DF scored poorly when compared with controls
o Say which things are the same or different - Grasping task: comparable with controls
o Location of the object – more about picking something up – accurately picking something up and recognising where it is in space
o DF was perfectly in line with controls – preserved spatial recognition - DF can still say where things are in space, this could be as the dorsal pathway of his visual pathway is not damaged
What do V1 and V2 do? Similarities and differences?
- V1 and V2 do relatively basic visual processing
o Share when looking at where things are and what they are
o But diverge, you have more activation going into the parietal cortex (spatial abilities) and another stream going down into the temporal cortex
o STS is also involved – ventral stream
What are the dorsal and ventral pathways?
- Shared processing in earlier visual areas and then these diverge
o Dorsal pathway is where
o Ventral pathway is what - Linked to the parietal and temporal cortex
What is the dorsal pathway?
- The occipito-parietal pathway
- The ‘where’ pathway
o helps determine where an object is
o analysing spatial configurations between objects - Specialised for spatial perception
What will a lesion in the bilateral parieto-occipital region do?
o “To the patient a chair is flat, though he knows from experience that his visual impressions are cheating him …. A stair is a flat inclined plane with no protruding steps, and yet he knows from the light and shade that he ought to see the steps ……”
- The patient was able to identify objects, but he was impaired at judging the distance/depth of objects relative to health control.
o Problem: processing of depth
What is the ventral pathway?
- The occipito-temporal pathway
- The ‘what’ pathway
o helps determine what we’re looking at - Specialised for object perception and recognition
What will damage to temporal-occipital regions do?
- Deficits in recognition following damage/lesion
- Leads to several types of agnosia
What will LOC lesions lead to?
- Not only was LOC severely damaged, but the remaining areas in the ventral stream showed no more activity
o Mainly damage to the ventral stream and has more damage with object recognition
Through what two visual streams does visual processing occur?
o Ventral ‘what’ stream – object recognition
o Dorsal ‘where’ stream - vision for action to objects
What is agnosia?
- Breakdown of the ventral and dorsal pathways
- From the Greek word for ‘lack of knowledge’
- The inability to recognise objects when using a given sense, even though that sense if basically intact
What are lesions?
- Non-human animals
- Damage brain area or impair its function and then observe the effect on task performance
o we can determine whether an area ‘is involved’ in task - Neuropsychology (humans)
- Look at behavioural, cognitive or emotional effects of damage occurring ‘naturally’ to the brain
o e.g. strokes, tumours, head trauma, neurodegenerative disease & neurological disorders – but PLASTICITY…
What is apperceptive agnosia? (simple terms)
o Failures in object recognition linked to problems in early perceptual processing
o Damage to both V1 and V2 areas – issues with ventral and dorsal pathways
What is integrative agnosia? (simple terms)
o Can see individual parts but unable to use this information to recognise things – issues with “wholes”.
What is associative agnosia? (simple terms)
o Can integrate parts to see wholes but issues with final recognition
o Fail at the last stage of perception
Can’t say what something is
What is prosopagnosia? (simple terms)
o Normal vision and recognition except for faces
What do individuals with apperceptive agnosia have (lesions)?
Right-sided parietal lesions
What do individuals with apperceptive agnosia broadly have trouble with?
- Patients may be able to identify conventional objects
- Recognition poor with unusual views, parts-separated objects
o But able to identify conventional objects even with poor discrimination of parts - Recognition poor in perceptual matching tasks
- People with damage to the parietal lobe cannot match objects which are inverted
- Can see some differences with images that have ‘a base’ – trucks have a base, but the keys don’t. So, when they know it should look a certain way, they can recognise what it should look like because they know it needs to be transposed
- Similarly, there was poor recognition performance with parts-separated objects.
- But the patients were able to identify whole objects with conventional views.
What is the perceptual problem in individuals with apperceptive agnosia?
The integration of spatial information
What are individuals with apperceptive agnosia able to identify and not identify?
o Able to identify conventional objects but sometimes have real issues with copying objects
o But recognition poor with unusual views, parts-separated objects,
o Able to identify conventional objects even with poor discrimination of parts
o Unable to draw copies of objects by extracting the relevant parts of it
What do individuals with integrative agnosia have (lesions)?
E.g. Patient HJA – impaired intermediate vision
o Bilateral lesions affecting lingual and fusiform gyri extending into inferior, posterior temporal lobe
