LTM Lecture Part 1 and 2

Introduction to Long-Term Memory

• Long-term memory (LTM) is a relatively permanent storage vault for a lifetime's worth of knowledge and experience.
• LTM is used to remember:
  • General knowledge (semantic memories)
  • Events from our lives (episodic memories)
  • Skills (procedural memories)

Distinguishing STM and LTM

• STM (Short-Term Memory) holds a small amount of information in an active, highly available state.
• LTM is a relatively permanent storage vault for a lifetime's worth of knowledge and experience.
• If you are currently thinking about something, it is in STM. If not, but it is accessible later, it is in LTM.

STM and LTM Continually Interact

• STM and LTM continually interact.
• STM sends information to LTM for storage.
• STM accesses information stored in LTM.
• LTM can increase STM's capacity by combining single pieces of information into meaningful chunks.

The Serial-Position Effect

• The serial-position effect demonstrates how information passes between STM and LTM.
• The effect shows that:
  • More words from the start of the list are recalled than the middle.
  • More words from the end of the list are recalled than the middle.

Why Does the Serial-Position Effect Occur?

• The primacy effect occurs because early list words are rehearsed more and enter LTM for durable storage.
• The recency effect occurs because late-list words are still in STM and are easily recalled.

Are STM and LTM Separate Systems?

• Some theories argue that STM and LTM are not separate systems, and that STM is simply a part of LTM that is activated at any given moment.
• However, studies on amnesic patients show a double-dissociation between STM and LTM, suggesting they are separate systems.

STM and LTM in the Brain

• STM and LTM involve separate brain areas, including the prefrontal cortex and hippocampus.
• The hippocampus is associated with LTM, but there is debate over whether it is also involved in STM processing.

The Hippocampus and LTM

• Traditionally, the hippocampus was believed to create LTM's, but not be involved in STM.
• However, later research suggests the hippocampus may also assist with STM maintenance.

Coding and Encoding

• Different external stimuli are stored in LTM in different formats/codes.
• The process of storing external stimuli in LTM is called encoding or coding.
• There are many types of coding, including:
  • Visual coding
  • Auditory coding
  • Semantic coding

Semantic Encoding/Coding

• Semantic coding is a type of coding in which the general meaning of a sentence or story is coded and stored in LTM.
• When recalling the information, the semantic representation appears in our minds.

Multiple Representations

• We can code multiple aspects of a stimulus and hold multiple representations of it in LTM.
• For example, we can recall the plot of a movie as semantic coding and picture the characters as visual coding.

Atkinson and Shiffrin's Model of Memory (1968)

• Atkinson and Shiffrin proposed the first major model describing human memory's structure.
• They suggested we have three major memory systems: STM, LTM, and sensory memory.

Squire's Model of LTM (1992)

• Squire proposed the first major model of LTM, which is still the main model today.
• He said we have two qualitatively different categories of LTM:
  • Declarative Memory (explicit memory)
  • Nondeclarative Memory (implicit memory)

The Biological Bases of Squire's Model of LTM (1992)

• The medial temporal lobe, including the hippocampus, is involved in LTM.

Key Takeaways

• By the end of this lecture, you should be able to:
  • Explain how STM and LTM differ at a functional level.
  • Explain whether or not STM and LTM are biologically distinct.
  • Explain how information is encoded/coded in LTM and what semantic coding is.
  • Explain how declarative and nondeclarative memory differ.
  • Name the different declarative and nondeclarative memory systems in Squire's (1992) LTM model.

Long-Term Memory Structure

• Long-term memory (LTM) is divided into declarative and non-declarative memory systems
• Declarative memory is further divided into episodic and semantic memory

Episodic and Semantic Memory

• Episodic memory: specific memories of personally experienced events (e.g., first day at university, breakfast today)
• Semantic memory: general knowledge, memories of facts, meanings, and concepts (e.g., capital of France, types of furniture)

Episodic Memory Tests

• Free recall: recalling information in any order
• Serial recall: recalling information in a set order (e.g., backwards)
• Cued recall: using cues or aids to recall information
• Recognition: identifying information as old (studied) or new (not studied)

Semantic Memory Tests

• Picture/object naming: naming familiar objects, often seen in pictures (e.g., scissors)
• Category fluency: naming as many category exemplars as possible in a set time (e.g., fruits)

Are Episodic and Semantic Memory Separate?

• Different feelings when recalling episodic and semantic memories
• Cognitive neuropsychology research shows brain lesions impact one or the other
• Cognitive neuroscience research shows distinct brain areas process both

Procedural Memory

• Stores knowledge of learned skills
• Created in three stages: cognitive, associative, and autonomous
• Example: tying shoelaces, writing a sentence, riding a bicycle

Priming

• Occurs when the presentation of one stimulus influences processing of a later stimulus
• Types: repetition priming, semantic priming
• Helps speed up mental processing in everyday life

Repetition Priming

• Presentation of a stimulus speeds up its processing (e.g., seeing "nurse" twice)
• Studied using picture recognition tasks

Patient H.M.

• Famous amnesic patient who underwent surgery to cure epilepsy
• Developed severe memory problems, including impaired episodic and semantic memory
• Could not form new episodic memories, but had excellent knowledge of words learned pre-surgery
• Showed separate declarative and non-declarative memory systems

Separate Declarative and Non-Declarative Memory Systems?

• Patient H.M. showed improved mirror tracing skills over time, but no recollection of learning the skill
• Patient H.M. showed intact priming, but impaired episodic memory
• Evidence suggests separate declarative and non-declarative memory systems that interact with each other