Memory

Highly Superior Autobiographical Memory

• Jill Price has highly superior autobiographical memory.
• She can remember every day of her life since February 5th, 1980.
• When tested with random dates, she can recall exact details (Parker et al., 2006).
• Jill has hyperthymesia, a rare syndrome where people can recall vast amounts of episodic memory in vivid detail.
• There are about 60-80 documented cases worldwide.
• For some, hyperthymesia can be a curse, making it difficult to forget negative past experiences.
• Some individuals with hyperthymesia use calendars to determine the current day.
• Jill's experiences highlight the extraordinary nature of memory and the importance of forgetting as a normal function.

Overview of This Week's Videos

• Part 1: Ways of thinking about memory
• Part 2: Sensory memory and short-term memory
• Part 3: Long-term memory
• Part 4: Working memory

Lecture Learning Outcomes

1. Identify and explain the different components of the multi-store model of memory (sensory memory, short-term memory, and long-term memory).
2. Define working memory, characterize its components, and explain how it is different from short-term memory.

A Definition of Memory

• Memory is a change in the brain or mind following an experience.
• Yavin Dudai defines it as "The retention of experience-dependent internal representations over time."
• It involves retaining, retrieving, and using information about stimuli, images, events, ideas, and skills after the original information is no longer present.
• Research focuses on distinctions between different types of memory.
• Different types of memory likely function in different ways.

Early Theories of Memory

• William James distinguished between primary and secondary memory in the 19th century.
• Primary memory: Current contents of consciousness.
• Secondary memory: Mental representations of the distant past, not currently in consciousness, requiring retrieval.

Content-Based vs. Process-Based Theories of Memory

• Content-based theories: Describe the different types of memory and their properties.
  • e.g., semantic memory for facts, episodic memory for experiences
• Process-based theories: Describe the processes and algorithms for holding memories in the mind.
  • e.g., encoding vs. consolidation vs. storage vs. retrieval
  • e.g., the Temporal Context Model, pattern separation in the hippocampus, retrospective vs. prospective working memory, etc.
• This lecture focuses on content-based theories.

The Many Types of Memory

• Sensory Memory
• Short-Term Memory
• Working Memory
• Long-Term Memory
  • Declarative Memory (Explicit Memory)
    • Events (Episodic Memory): Specific personal experiences from a particular time and place.
    • Facts (Semantic Memory): World knowledge, object knowledge, language knowledge, conceptual priming
  • Nondeclarative Memory (Implicit Memory)
    • Skills (Procedural Memory):
    • Perceptual Representation System: Perceptual Priming
    • Classical Conditioning: Conditioned responses between two stimuli
    • Nonassociative learning: Habituation, sensitization
    • Medial temporal lobe, middle diencephalon, and neocortex
    • Basal ganglia and cerebellum
    • Perceptual and association neocortex.
    • Skeletal muscle
    • Reflex pathways

The Multi-Store Model of Memory

• Atkinson & Shiffrin (1968) proposed the multi-store model.
• The model includes:
  • Sensory memory
  • Short-term memory
  • Long-term memory
• Information flows from sensory memory to short-term memory via attention.
• Information can be transferred from short-term memory to long-term memory via rehearsal.
• Information can be retrieved from long-term memory back into short-term memory.

Sensory Memory

• Sensory memory is a buffer that briefly holds all information arriving at our senses.
• Characteristics:
  • Extremely large capacity
  • Extremely short timescale
• Separate sensory memory store for each sense:
  • Vision: iconic memory (less than 1 second duration)
  • Audition (hearing): echoic memory (up to 10 seconds duration)
• New information constantly overwrites old information.

Iconic Memory

• Iconic memory is sensory memory for visual information.
• Explains the persistence of vision, where new sensory information blends with existing information.
• Examples include:
  • Sparkler's trail of light
  • Illusion of motion in films and zoetropes
  • Superpositions in thaumatropes

Echoic Memory

• Echoic memory is sensory memory for auditory information.
• Speech perception and conversation rely on echoic memory.
• Example: Responding to a question after a delay because the information was briefly stored in echoic memory.

The Duration of Sensory Memory

• Sperling (1960) investigated the duration of sensory memory.
• Whole report: Participants reported as many letters as possible from a displayed array.
  • Average: 4.5 out of 12 letters (37.5%)
• Partial report: Participants heard a tone indicating which row to report immediately after the array disappeared.
  • Average: 3.3 out of 4 letters (82.5%)
• Delayed partial report: Tone presented after a delay.
  • Performance rapidly worsened as the delay increased.

Short-Term Memory

• Short-term memory retains a limited amount of information for a limited time.
• Characteristics:
  • Limited capacity
  • Short timescale (15-20 seconds without rehearsal)
• Rehearsal can extend the duration of information in short-term memory.
• Rehearsal is a conscious, effortful process.

What is the Duration of Short-Term Memory?

• Peterson & Peterson (1959) measured the duration of short-term memory using a task where participants had to remember trigrams (e.g., TGH, SRD, CLS, GDA) after varying delay periods.

What is the Capacity of Short-Term Memory?

• Digit span task measures capacity (Gilker, 1992).
• Typical result: 5-9 items (Miller's law of 7 oldsym
  pm 2).
• What constitutes an 'item'?

Chunking

• Small units can be combined into larger, meaningful units to increase storage capacity.
  • e.g., 0-4-1-7-2-1-0-0-2-2 vs. 0417-210-022
• A chunk is a collection of strongly associated elements, weakly associated with other chunks.
• Chunking is a skill that can be improved.
• Ericcson et al. (1989) trained a student with average memory to use chunking.
  • S.F. initially had a digit span of 7.
  • After 230 1-hour sessions, S.F. could remember up to 79 digits by chunking.

Long-Term Memory

• Long-term memory retains very large amounts of information for very long durations.
• Information must be retrieved from long-term memory to be used.

Declarative and Non-Declarative Long-Term Memory

• Declarative memory requires conscious effort for recall.
  • Information must be 'declared' to consciousness.
  • Also called explicit memory.
  • Subtypes: episodic and semantic memory.
• Non-declarative memory can be recalled without effort.
  • Sometimes without awareness.
  • Also called implicit memory.
  • Subtypes: learned skills, habituation/sensitisation, conditioned responses.

Types of Declarative Long-Term Memory

• Semantic memory: Memory for facts and concepts.
  • Examples: Paris is the capital of France, your mother's name, dogs are furry.
• Episodic memory: Memory for events.
  • Examples: What you did last New Year's Eve, your first kiss, what you ate for breakfast this morning.

Double Dissociations

• Memory systems are often described in dichotomies.
• Double dissociation is the gold standard in neuropsychology to confirm these are truly distinct systems.
• Analogy: Some people are blind but not deaf, others are deaf but not blind, indicating independence of sight and hearing in the brain.
• To show two memory systems are distinct, look for patients with a deficit in one system but not the other.

Double Dissociation: Episodic Memory and Semantic Memory

• Patient K.C.
  • In 1983, K.C. had a motorbike accident.
  • Closed head injury with damage to the medial temporal lobe and hippocampus.
  • Severe anterograde amnesia and some retrograde amnesia for episodic memory.
  • No episodic memory: cannot relive past events.
  • Intact semantic memory: can remember general information and facts about the past.
• Patient L.P. ('Italian woman')
  • Had severe encephalitis in 1984, damaging the left temporal lobe.
  • Impaired semantic memory but preserved episodic memory.

Working Memory (Versus Short-Term Memory)

• Working memory is a limited-capacity system for temporary storage and manipulation of information for complex tasks (comprehension, learning, reasoning).
• Distinction between short-term and working memory is subtle but important.
• Short-term memory is a component of working memory.
• Short-term memory holds information; working memory processes and manipulates it.
  • Short-term memory: Repeat the digits.
  • Working memory: Repeat the digits in reverse order.

A Model of Working Memory

• Baddeley & Hitch (1974) proposed a model of working memory.
• The phonological loop and visuospatial sketchpad are short-term memory stores with different coding types.
• The central executive coordinates and manipulates information from these stores.

The Phonological Loop

• Specialized for auditory and linguistic information (spoken words, written language, sounds).
• Has a fixed duration.
• Three sources of evidence:
  1. The phonological similarity effect
     • Letters/words are most likely to be mistaken for similar-sounding ones.
  2. Articulatory suppression
     • Repeating a separate word aloud interferes with working memory for verbal stimuli.
  3. The word length effect
     • Memory is poorer for lists of long words than short words.
     • Long words take longer to rehearse; fewer fit in the loop's duration.

The Visuospatial Sketchpad

• Stores visual and spatial information (pictures, objects, maps).
• 'Mental images' are retained in the sketchpad.
• Evidence for mental imagery comes from studies of mental rotation.

The Central Executive

• Controls the focus of attention.
• Focusing, switching, dividing attention.
• Suppresses irrelevant information.
• Retrieves and manipulates information from other stores.
• Makes working memory 'work'.