Long Term Memory: Structure, Types, and Processes

Long Term Memory Structure and Processes

• Atkinson and Shiffrin proposed the Modal Model of Memory in 1968.
• Long-term memory (LTM) is for relatively permanent storage of information over long periods.
• LTM has a relatively permanent duration and a relatively unlimited capacity.
• LTM is acquired across a lifespan.

Types of Long Term Memory

• Explicit (Declarative) Memory is consciously recalled, with awareness internally or externally.
  • Episodic memory involves experienced events throughout life that can be relived through mental time travel, such as remembering a party.
  • Semantic memory includes knowledge, concepts, and facts about the world.
• Implicit (Non-Declarative) Memory operates without complete awareness.
  • Procedural memory involves skills and actions.
  • Priming is a type of implicit memory.

Serial Position Curve

• The Serial Position Curve, studied by Murdoch Jr. in 1962, illustrates how the position of words in a list affects recall accuracy.
• The primacy effect is remembering items at the beginning of a list because they are rehearsed more and experience less interference.
• The recency effect is remembering items at the end of a list best, better than items in the middle or beginning.

Primacy Effect

• Dewey Rundus (1971) researched the primacy effect.
• Presenting words separated by 5-second intervals and using articulatory suppression to prevent memorization was studied.
• Preventing rehearsal leads to problems in remembering items at the beginning of a list.
• The number of rehearsals tends to be higher at the beginning of the list and decreases toward the end.

Recency Effect

• Glanzer and Cunitz (1966) investigated whether the recency effect relates to short-term memory, if STM plays a role then study waiting some time before you start writing those elements.
• In a study, one group immediately recalled items, while another group counted backwards for 30 seconds before recall.
• Participants recalled rehearsed items better but struggled with items at the end of the list after the delay.
• Long-term memory relies on rehearsal, transferring information from short-term to long-term memory.
• The recency effect only involves information recently learned if it doesn't pass into Long Term memory.

The Hippocampus

• Hippocampus: Latin for seahorse, with two in each hemisphere.
• The hippocampus formation is implicated in memory formation.

Patient HM

• Patient HM, studied by Brenda Miller, suffered from seizures that originated in the medial temporal lobes, including the hippocampus.
• Surgical removal of these areas stopped his ability to form new long term memories.
• Amnesia refers to the loss or disorder of memory.
  • Anterograde amnesia is the inability to form new memories.
  • Retrograde amnesia is the inability to access old memories.

Declarative vs Non-Declarative Memory

• HM lost explicit memories for events or knowledge after surgery and could not encode them.
• HM retained good implicit new memories but wouldn't remember meeting Brenda Milner

Semantic and Episodic Memory

• Endel Tulving researched semantic and episodic memory.
• Patient KC suffered damage to the medial temporal lobe and hippocampus due to a bike accident.
• KC lost episodic memory, experiencing both retrograde and anterograde amnesia for past events, but retained semantic memory.
• Semantic and episodic memory are distinct but used together, with semantic knowledge influencing how episodic memories are encoded.
• Petrican et al. studied the interaction between semantic and episodic memory in older adults using newspaper articles of past events.
• The study calls the shift from episodic to semantic memory semanticization.

Implicit Memory

• Implicit memory involves non-conscious remembering.
  • Procedural memory is related to skills and actions.
  • Priming occurs when exposure to a stimulus affects future behavior without conscious memory of the stimulus; for instance, smelling pizza may cause a craving later without remembering the smell itself.
• Peter Graf et al. (1985) found that individuals with amnesia and those with normal brains could rate lists of words without being told to remember them.

Memory Recall

• Word stem tasks, involving exposure to words, were completed using existing knowledge.
• Explicit recall tasks ask where certain words were presented.

Biological Basis of Memory

• Karl Lashley (1930s) studied the biological basis of memory.
  • Rats were trained to run mazes.
  • Systematic lesioning of different brain areas shows where memories might be stored.
  • Engrams are not stored in a single place.
• Engrams are the physical basis of memory involving the structure and interaction of neurons and synapses distributed across the brain.
• Consolidation is how engrams become imprinted into the nervous system.
  • Consolidation affixes or connects engrams to long-term memory.
  • This process stabilizes memory traces and happens at the synaptic level.
  • At the systems level, memory involves networks of neurons and connections.
  • Memory is stored between connections of neurons

Donald Hebb

• Donald Hebb (Lashley's student) proposed, "Neurons that fire together wire together." Two neurons firing action potential at the same time will form stronger connections.
• Long-term potentiation (LTP) strengthens connections, increasing neurotransmitters and vesicles.
• Long-term depression (LTD) weakens connections.

Memory Storage

• Memories are stored across the entire brain.
• The hippocampus serves as a "memory index" in the temporal lobe, initiating or locating memories and projecting them to the cortex.
• Synaptic theory of memory suggests that memories are relative weights or connection strengths, between neurons.
• In the hippocampus, LTP and LTD create networks of neurons with strong synapses but weak connections without light signals.
• Over time, the cortex forms connections with other neurons connected with the hippocampus neurons; allowing its own networks.

Encoding Things into Memory

• Successful encoding depends on attention.
• Mnemonic devices are learning aids or strategies that enhance recall like PEMDAS, ABCs, and ROYGBIV.

Levels of Processing

• Shallow processing (superficial) leads to less memorable information.
• Deep processing (meaningful) enhances memorability, studied by Craik and Tulving (1975).
• Self-reference effect, researched by TB Rogers et al. (1977), show that information that is meaningful and self-relevant improves memorability

Factors for Remembering

• Survival is one of the most important factors in remembering things, if they help you survive
• Visual imagery means you are more likely to remember things if you picture them in mind
• Practice tests make it more likely to remember if you have been tested on it

Memory Retrieval

• Retrieval reactivates or reconstructs memories from storage.
• Recall involves generating remembered information independently.
• Recognition involves identification of selecting previously remembered information from several options.
  • Retrieval cues are hints that facilitate recall.
  • Cued recall is better than free recall

Encoding and Retrieval

• Context-dependent memory (Godden and Baddeley) demonstrates better recall when the physical or external context during encoding and retrieval is similar.
• State-dependent memory (Goodwin et al.) shows memory is best when internal/mental state context matches during encoding and retrieval.
• Mood-dependent memory (Eich and Metcalfe) is best when mood matches between encoding and retrieval.