Long-Term Memory and Amnesia

Long-term Memory

• Long-term memory, amnesia, and varieties of long-term memory are to be discussed.

Multi Store Model - Atkinson & Shiffrin

• The model illustrates the flow of information from environmental input to long-term memory.
• Environmental input is processed as sensory input (sights, sounds, etc.).
• Attention filters sensory input into sensory memory.
• Information can undergo maintenance rehearsal in short-term memory (STM).
• Elaborate rehearsal leads to storage in long-term memory (LTM).
• Forgetting occurs through decay or displacement in sensory memory and STM.
• Forgetting in LTM occurs through interference or retrieval failure.

Duration and Capacity of Memory Stores

• Sensory memory has a duration of less than 1 second and a large capacity.
• Short-term memory has a duration of 30 seconds and a limited capacity.
• Long-term memory has an unlimited duration and a large capacity.
• Differences in duration and capacity provide evidence for distinct types of memory.

Evidence for Distinction Between Short-Term and Long-Term Memory

• Two key pieces of evidence:
  • Serial position curve
  • Dissociations and brain damage

Serial Position Curve

• In free recall, more items are recalled from the start of the list (primacy effect) and the end of the list (recency effect).
• First items recalled tend to be from the end of the study list.
• Recency Effect: Items are still in STM.
• Primacy Effect: Longest rehearsal makes items more likely to be successfully stored in LTM.

Effects of Delay on Serial Position Curve

• Primacy effect is not affected by delay between study and test.
• Recency effect disappears as STM decays with delay.

Selective STM Deficit

• Patient KF suffered left parietal-occipital lobe damage in a motorcycle accident and had some speech and language impairment.

Patient KF (Warrington & Shallice, 1969)

• Impaired STM (digits span).
• Preserved LTM (Paired-associated learning).
• KF's digit span was significantly lower than normal.

Patient KF (Shallice & Warrington, 1970)

• Immediate free recall of a 10-word list showed recency effect for only the last word, indicating a reduced STM span.

Patients KF, JB, WH (Warrington, Logue & Pratt, 1971)

• Immediate free recall of a 10-word list.
• A 30-second delay reduces recency effect (but only last word!).
• No effect of delay on primacy effect.

Amnesia

• Patient NA was a young soldier who suffered a bizarre accident in his early twenties – a fencing foil pierced his brain.
• Amnesia can result from brain trauma (accidents, lesions to treat epilepsy), damage from alcoholism, or electroconvulsive therapy (ECT).
• Two Components of Memory Loss in Amnesia:
  • Retrograde: Loss of pre-trauma memories.
  • Anterograde: No new memories post-trauma.

Preserved Functions in Amnesiacs

• Knowledge of language; can communicate and understand normally.
• Sufficient memory to keep track of what is being said within a conversation.
• No deficit in STM and digit span.
• No deficit in IQ.

Amnesic K. C.

• Motorcycle accident causing severe bilateral damage to the medial temporal lobe.

Warrington & Weiskrantz (1970)

• Amnesiacs performed worse than controls on memory tests like recall and recognition.

Cohen & Squire (1980)

• Word pair learning in various types of amnesiacs.

Tasks Measuring Working Memory & Long-Term Memory

• Card Sorting task: working memory, executive function.
• Face Recognition task: long-term memory.

Dissociation Between STM and LTM

• Dissociation between STM and LTM is evidence of different memory systems.
• K.M. had frontal lobe damage (WM).
• H.M. etc. had hippocampus damage (LTM).

Performance of Normal, N. A., K. C., K. F.

• Dissociation between STM and LTM is evidence of different memory systems.

Alternative Conceptions of Working Memory

• Information can be stored in LTM without passing through STM.
• STM deficit is an inability to manipulate or use, rather than inability to store, information in working memory.
• Working memory is just an "activated" area of LTM under the current focus of attention (Cowan, 1999).
• STM deficit is a problem of the central executive’s ability to focus attention in LTM.

Long-Term Memory Taxonomy

• Long-term memory is divided into declarative (explicit) memory and nondeclarative (implicit) memory.
• Declarative memory includes events (episodic memory) and facts (semantic memory).
• Nondeclarative memory includes procedural memory, perceptual representation system, classical conditioning, and nonassociative learning.

Intact LTM in Amnesia: Procedural Memory

• Amnesiacs show fewer errors over time, indicating intact learning.

Declarative vs. Procedural

• Declarative: Conscious memory.
• Procedural: Perceptual-Motor learning.

Intact LTM in Amnesia: Perceptual Priming

• Amnesiacs show fewer errors on the second identification test, indicating perceptual identification.

Procedural Memory: Not only motor skills?

• Cohen & Squire (1980) demonstrated that amnesiacs could be trained in reading backward-image words.

H.M. Tactile Maze Learning

• What did H.M. learn and not learn?

Declarative vs. Procedural Memory

• Declarative: "knowing that…", conscious memory.
• Procedural: "knowing how…", motor & cognitive skills.

Explicit and Implicit Tests of Memory

• Explicit tests: Free recall, cued recall, recognition.
• Implicit tests: Fragment identification, word-stem completion.

Explicit vs. Implicit Tests of Memory

• Explicit Tests:
  • Free Recall: Write down as many words as you can remember from the study list.
  • Cued Recall: Complete these word stems (FL, IS) with words you remember from the study list.
• Implicit Tests: No instruction to consciously use memory.
  • Stem Completion: Complete with a word (FL, IS).
  • Fragment Identification: What word is this? (FOE_)

Warrington & Weiskrantz (1970)

• Amnesiacs performed worse than controls on explicit memory tests like recall and recognition.
• Amnesiacs equal to controls on implicit memory tests like word fragment identification and word stem completion.

Declarative vs. Non-Declarative

• Declarative: Conscious memory.
• Non-Declarative: Non-Conscious memory?
• Explicit vs. Implicit.

Summary: Amnesia

• Amnesiacs are impaired in declarative memory tasks but perform normally in non-declarative memory tasks.
• Explicit and Implicit memory tasks access different types of long-term memory.

Amnesics Learning Real Skills

• Amnesic MT trained to find her way around rehabilitation unit (Brooks et al., 1999).
• No accurate explicit memory, preserved implicit & procedural learning.

Brooks et al. (1999)

• Incremental learning in real and virtual environments.
• 8 weeks of daily training on routes like Bedroom to Dining Room, Bedroom to Gym.
• After learning, could still find route weeks later BUT did not know that she knew the route.

Dissociations Between Explicit and Implicit LTM

• Dissociations between explicit and implicit LTM tasks is evidence of different memory systems.

Long-term Episodic Memory

Episodic Memory

• Encoding
• Storage & Consolidation
• Retrieval

Consolidation in Long-Term Memory

• Memories initially fragile and easily disrupted.
• Become consolidated (stronger) over time.
• Pinel (1969) experiment with rats learning spatial location and electroconvulsive shocks.

What is Consolidation?

• Strengthening (synaptic & structural).
• Hippocampus plays a key role in consolidation and other areas in medial temporal lobe.

Consolidation

• Time helps consolidation.

Muller & Pilzecker (1900)

• Learned 2 word lists (List 1, List 2).
• No delay or delay between Lists.
• Recall of List 1 much better after delay.
• Memory initially fragile and easy to disrupt by learning List 2.
• Delay allows consolidation of List 1 memory
• 28\%
• 48\%.

Consolidation

• Sleep helps consolidation.

Gais, Lucas, Born (2006)

• Tested the effect of sleep deprivation on forgetting between first and second recall tests.
• Learn list: Water - Wasser Train - Zug (+ 1st recall test) Girl - Mädchen ….

Gais, Lucas, Born (2006)

• Time interval held constant.
• Sleep deprivation increased forgetting.
• Sleep helps consolidation and protects learning.

Consolidation

• Sleep protects learning from interference (new information does not overwrite learning).
• Sleep actively promotes consolidation.
• During slow-wave sleep, neuronal patterns formed during learning are reactivated and strengthened.

Consolidation Is An Ongoing Process

• Connections at the synaptic & structural level.
• Reorganization: initial dependence on hippocampus & medial temporal lobe to more permanent representations in neocortical areas which are damaged in amnesia.

Summary of Lecture Topics

• Evidence for distinction between STM and LTM
• Amnesia and Types of Long-Term Memory
• Consolidation in Long-term Memory