Cognitive Psychology C81COG5. Memory – Structure & Processes

Dr Jonathan Stirk

Background Reading

Baddeley, A.D. (1999). Essentials of human memory. Hove, UK: Psychology Press.– Chapters 2 & 3

Overview

Dichotomies in the description of memory Memory Processes Structural attempts to separate STM and LTM

– forgetting by decay or interference – capacity differences – coding by sounds or by meanings?

The simple multi-store model fails, so– an alternative to structural distinctions?– a revised model, based upon “working

memory”

Common distinctions in the description of memory

Short-term (1°) vs. Long-term memory (2°)– The phone number of your dentist (look it up in the

phone book, then dial it) vs.– A very familiar phone number (e.g. Home)– Distinction based on temporal aspects of memory

Temporary and fleeting vs. more permanent and stable

Common distinctions in the description of memory

MEMORY(LTM)

Procedural [non-declarative]

(Skills, priming, conditioning)

Episodic Semantic

Declarative(Knowledge)

Open to intentional retrieval

Larry Squire (1992)

Measured through performance rather than conscious

recall/recognition

Procedural vs. Declarative LTM

How to tie your shoelaces vs. the name of the current US president

How? That?

Episodic vs. Semantic LTM

What did you have for lunch today? vs. What kinds of animals are canaries?

Semantic Memory – Tulving (1972)

“It is a mental thesaurus, organised knowledge a person possesses about words and other verbal symbols, their meanings and referents, about relations among them, and about rules, formulas, and algorithms for the manipulation of these symbols, concepts, and relations.”

Memory Processes

Memory Structure - Multi-store Model (Modal model)

DECAY DISPLACEMENT INTERFERENCEForgetting mechanisms

Short-term store

Long-term store

Sensory

registers

(Atkinson & Shiffrin,1968)

Differences Between Memory Stores

Evidence for separate and distinct memory stores has been supported by looking at:– Forgetting mechanism(s)– Storage capacity– Temporal duration– Effects of brain damage

Properties Of The Short Term Store

FORGETTING MECHANISMS– Loss of information through autonomous decay – Distraction results in loss of information (Peterson &

Peterson, 1959)

LIMITED STORAGE CAPACITY – STM span limited to 3 items (pure STM capacity limit;

not Miller’s 7+-2; see next slide)– Recency in serial recall curve is read-out from Primary

Memory (Craik, 1964) – Delayed recall eliminates recency (Glanzer & Cunitz,

1966)

Chunking Allows More Information To Be Stored

Miller (1956) suggested that memory capacity is not limited by number of items that can be stored but by number of chunks. Chunking requires support by LTM

Evidence for forgetting by decay in a STM task

Peterson & Peterson (1959) distracter task1. Listen to a consonant trigram (e.g. SKB)2. Now start counting backwards in threes from

this number (e.g. 751)– Varied how long they did this for (variable

delay to allow the counting to have an effect)3. Now recall the trigram4. Repeat 1-3 for more trials/trigrams

Q. What % of trigrams are correctly recalled, and how is this influenced by the delay between presentation and recall?

Loss Of Information From STM By Decay

Delay between presentation of trigram & recall, during which participants are distracted by counting backwards, & during which forgetting is possible

Interpretation: We lose information from STM through autonomous decay when information is left unattended.Around the 1960’s forgetting in LTM was thought to be by interference

See also Brown (1958)•Also known as Brown-

Peterson distracter task

Results

Glanzer & Cunitz (1966) – Further evidence of 2 stores (STS & LTS)

Primacy Effect

Usual recency effect (about 3

items!)

Recency effect is

eliminated by delay

LTMSTM

Other factors effecting the serial-position curve: Word Frequency & STM

00.10.20.30.40.50.60.70.80.9

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Serial (List) Position

Pro

por

tion

Cor

rect high freq

(common)

low freq (rare)

LTM STM

Raymond, 1969

Double Dissociation

The primacy effect is altered by– The word frequency of

items used in the task Low frequency words

→ lower recall of first few items in list

The recency effect is altered by – the use of a delay

between learning & recall

distracter task → lower recall of last items in list

Double Dissociation: two situations or theoretical entities are affected in opposite ways by one or more independent variables

But NOT by a delay! But NOT by word frequency!

Recall These 8 Letters In Order

1. V C B D G E P T

2. R F Q P L N Z K

Recall These 8 Letters In Order

1. V C B D G E P T

2. R F Q P L N Z K

Did you perform better for list 2?

Further Properties Of The Short Term Store 

Coding Coding in LTM is thought to be semantic (based

on meaning)/associative. What about coding in STM then?

– Evidence for Acoustic codingConfusions in recall between items which

have similar sounds (Conrad, 1964; RLTKSJ →RLCKSA)

– Categorical but non-associative storageMeaningful relationships between words

are not appreciated (Tulving & Patterson, 1968; )

Summary of Properties Of STM

The short-term store retains a limited amount of information for a brief interval, and what it retains is categorical but non-associative items using an acoustic code– Limited capacity– Short duration (information lost by decay if

not rehearsed)– Phonologically coded

Problems With Earlier Interpretation of Peterson & Peterson’s (1959) exp’t!

Keppel & Underwood (1962) An average taken for each subject across numerous trials This assumes no performance change across trials

After an 18 sec delay, PI from triplets presented on earlier trials builds up.

Pro-active interference/inhibition (interference from info presented before the to be remembered info)

No forgetting on trial 1, some on 2, more on 3

Problem: Evidence of Semantic Coding In a STM task

Warren & Warren (1976)

1. S hears PRINCE, KNIGHT, QUEEN (the “memory set”)2. 10 seconds of a distracter task3. Subject recalls the “memory set” (“Prince…”)4. Next trial sometimes contains a homophone-related set

e.g. MORNING, NOON, EVENING5. 10 seconds of distraction, etc, etc

Question - Do subjects ever confuse KNIGHT and NIGHT in the recall of the homophone-related set? (Is night offered in error in the recall of MORNING, NOON, EVENING?)

Answer - YES, therefore there has been some semantic processing of these words even though they are in a STM task

Separate Stores?

So evidence for 2 separate stores is not conclusive!

Rather than focusing on structure, why not look at the processing of information instead?– Craik & Tulving (1975)

Levels Of Processing Approach (Craik & Tulving, 1975)

Structural model breaks down– Atkinson & Shiffrin (1968)

Rehearsal always enhances transfer to LTM Not true!

Remembering is influenced by the “level of processing” during input (e.g. visual processing vs. semantic processing)

The emphasis is now upon process rather than structure

Craik & Lockhart (1972)- Levels of processing hypothesis

Depth of processing predicts durability of memory

Craig & Tulving (1975) - List of visually presented, unrelated words.

3 groups each with a different decision task – 1. Is the word in CAPITALS? – 2. Does it rhyme with “ate"?– 3. Is it a type of fish? Or does the word fit into the

following sentence? Measured latency (decision time) Then surprise memory test – recognition from

list of targets & distracters

Craik & Tulving’s Results

As the depth of processing increases decisions take longer to make (latencies increase – red figures)

and Unexpected

recognition improves (blue bars)

0.614

RED = latencies (secs)

0.689

0.746

Updating The Multi-store Model Of Memory

Baddeley & Hitch (1974) Model emphasises both storage AND processing Not unitary – verbal /visual-spatial subsystems Original incarnation was tripartite (3 components)

Working Memory

Central executive: directs and controls all WM functions; can be thought of as ‘attention’. Integrates info

Visuospatial scratchpad/sketchpad: a system for holding visual information

Articulatory/phonological loop: a system for holding and recycling auditory/acoustic information– Rehearsal/Articulatory loop : a process for recycling,

using subvocalization– Phonological buffer/store: a structure for holding acoustic

information

Working Memory Updates

Later version (Baddeley, 2000) incorporate an “episodic buffer” which time-stamps memories– So we know when something happened and not

just that it happened Later versions split the articulatory loop and

visuo-spatial sketch pad into two dual slave systems which are used by the CE