Lecture 16 - Memory and Perception Flashcards
1
Q
How is memory not a single function?
A
- Memory is not a single function
- Episodic – memory of specific events e.g. where you were during 9/11
- Semantic – memory for facts e.g. dopamine hypothesis
- Working – short term, rehearsal e.g. phone numbers (briefly)
- Procedural – motor memory e.g. riding a bike/playing piano
- These types of memory can be dissociated from each other and disrupted independently
- (E.g. by different types of lesion)
- Damage to memory is often referred to as amnesia
2
Q
Describe the neurology of memory
A
- Hippocampus, amygdala and related structures in the medial temporal lobe (MTL)
- Medial = inside
- Fornix = major output of the hippocampus
- Mammillary body = further output ~ pushing towards thalamus (information relay station)
- Amygdala = emotion processing
3
Q
What is anterograde amnesia?
A
- Poor ability to acquire new information
- Information acquired before damage is relatively spared, especially further back in time
- Also, information in working memory (ongoing rehearsal) is spared
- Specifically:
- Impaired declarative (explicit) memory: episodic and semantic
- Relative preservation of non-declarative (implicit) memory:
- perceptual (familiarity with stimuli)
- procedural (motor skills & habits)
4
Q
What causes anterograde amnesia?
A
Disorders e.g. Korsakoff’s syndrome
- Thiamine (vitamin B1) deficiency
- Due to alcoholism: poor diet and impaired absorption of thiamine from intestine
- Produces bilateral degeneration of mamillary bodies
Temporal lobectomy (1950s)
- E.g. for patients with intractable seizures
- Bilateral removal of temporal lobes
5
Q
Who was HM?
A
- Henry Molaison (1926-2008)
- Major seizures (epilepsy) since 16 years of age
- Drugs failed to contain seizures
- Surgical bilateral removal of anterior hippocampal regions at age 27 (1953)
- Important case in neuropsychology of memory:
- Circumscribed lesion (surgical)
- Surgery successful in combating epilepsy
6
Q
What were some of HM’s deficits?
A
- Pure deficits: IQ unaffected by surgery, no personality change or other deficits outside memory
- Even within memory, deficits are specific to the formation of new memories
7
Q
What happened to HM’s working memory?
A
- Intact working memory:
- Normal digit span (e.g. repeat the sequence: 5 3 8 2 9 1 6)
- Unless interrupted (constant rehearsal)
- Rate of forgetting within normal range
- Can hold a conversation, but later that day will not remember having held it
8
Q
What happened to HM’s semantic and episodic memory?
A
- Semantic memory disrupted, absence of new episodic memory:
- Language essentially frozen in 50’s
- Reported date and age as prior to operation
- Could not remember events or people met post-operation
- Could not learn location of new home
9
Q
What happened to HM’s ability to learn new motor skills?
A
- Could learn new motor tasks
- E.g. typical improvement on mirror tracing task (Milner 1962, 1965)
- Improvements in short term. Lost when pushed to LTM
- Deficits specific to semantic & episodic memory
10
Q
What are dissociations (experimental design)?
A
- Some tasks impaired, while others spared
- Suggests these tasks use different resources or regions
- E.g. semantic dementia patients: impaired semantic, spared episodic
- Problem: maybe one task is more difficult, so it will always fail first
- “Solution”: Double Dissociations
- One patient group: Task A spared, Task B impaired
- Other patient group: Task A impaired, Task B spared
11
Q
What is the difference between anterograde and retrograde amnesia?
A
- Anterograde = since lesion
- Retrograde = prior to legion
12
Q
Describe the neurology of retrograde amnesia
A
- Hippocampus, amygdala and related structures in the medial temporal lobe (MTL)
- More amygdala-driven than hippocampus-driven
13
Q
How was HM affected by retrograde amnesia?
A
- Temporally graded retrograde amnesia:
- Old memories (childhood) intact
- Memories immediately before lesion lost e.g. forgot death of favourite uncle in 1950
14
Q
What do patients like HM suggest about the neurology of memory?
A
- Patients like HM suggest that the hippocampus does not store memories - old memories are preserved
- Role of hippocampus in memory not yet completely understood
- It may enable consolidation of new memories, which are stored elsewhere
- This consolidation process must take time possibly decades
15
Q
What is the consolidation timeline?
A
- Testing retrograde amnesia:
- HM: photos of celebrities suggest retrograde amnesia spans decades, with more distant memories relatively preserved (Marslen-Wilson & Teuber, 1975)
16
Q
Describe the neurology of vision
A
- Occipital lobes and surrounding temporal and parietal
- Including PVC, ventral and dorsal streams
- Damage to these systems can cause agnosia (damage to the ventral) or optic ataxia (damage to the dorsal)
- Agnosia = the inability to recognize. A lack of knowing or perception
- Optic ataxia = deficits in spatial perception, visuospatial processing and visual guidance of action
17
Q
What is visual agnosia?
A
- Agnosia = the inability to recognise. A lack of knowing or perception
- Agnosia can come in many flavours; visual, auditory, somatosensory etc.
- Modality specific: individuals with visual agnosia would be able to name an object through touch
18
Q
What are the two types of visual agnosia?
A
- Types of visual agnosia:
- Apperceptive: unable to perceive full shape of object despite intact low-level processing
- Associative: ability to perceive shape, but inability to recognize it, e.g. to name it
- Visual agnosia not due to deficit in ‘early’ perception: e.g. acuity, field cut, loss of colour vision
19
Q
Describe apperceptive visual agnosia
A
- Unable to perceive full shape of object despite intact low-level processing. Inability to extract global structure
- Intact low-level perception
- Acuity
- Brightness discrimination
- Color vision
- Evidenced by impairments in drawing, copying and visual recognition, even of common objects
- Can see parts, but not whole
- Patient D.F – reason we know so much about dual stream visual processing
20
Q
Describe associative visual agnosia
A
- Intact ability to recognise the whole form of shapes
- No problem copying figures
- However, inability to draw from verbal instruction or to recognize objects using vision.
- E.g. a bike described as “a pole with two wheels” or a farmer observing a picture of a cow, which he couldn’t name, made “milking” movements with his hands. These movements signalled to him that he was looking at a cow
21
Q
What is prosopagnosia?
A
- Can be characterized into two types: associative and apperceptive
- Apperceptive prosopagnosia is defined as the inability to even perceive and cognitively process faces
- Associative prosopagnosia is defined as inability to recognize or apply any meaning to the face, despite perceiving it (can still identify individuals through voice, hairstyle etc.)
- Tends to involve damage to the fusiform gyrus in the lower part of the occipital and temporal lobe
- Usually right-sided
- ‘Fusiform face area’ (FFA) = renamed as a face area due to so many corroborating studies
22
Q
Are faces special? (experts)
A
- We are experts at processing faces
- Faces tend to include all the same features (eyes, nose, mouth), and very similar features are present in different individuals (e.g. family members), but we still recognize individuals well
- The particular configuration of features is unique to an individual
- Face-processing involves perception of the configuration as well as the features
- A specialized face-processing system in the brain may process faces ‘holistically’ (as a whole), including configural information
23
Q
Are faces special? (difficult)
A
- Faces are just difficult
- Most ‘prosopagnosics’ have difficulty recognizing differences within other categories e.g. types of car, breed of dog, cows in a herd (when we see similar but different of)
- The FFA is not only concerned with faces:
- Also active when observing pictures of birds or cars (Gauthier et al., 1999, 2000)
- If faces are special, why are ‘pure’ prosopagnosics so rare?
- The idea that faces are ‘special’ (with dedicated neural & cognitive processing systems) is still controversial
