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