Lecture 1: Short Term and Working Memory
Outline
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What is memory?
The Short Term / Long Term distinction
Baddeley’s model of Working Memory
Evidence for Baddeley’s model
The episodic buffer
By the end of the lecture you should have learned:
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Why a distinction is made between short and long term
memory
Key experiments that provide evidence for the 3 original
components of Baddeley’s model of Working Memory
Why the original model was revised
History of the STS/LTS distinction
1890 - William James draws distinction between primary and
secondary memory.
PRIMARY MEMORY
SECONDARY MEMORY
Reward portion of present
space of time
Linked to conscious experience
Genuine past
Unconscious - permanent
Retrieval is effortless
Retrieval is effortful
The development of computers in the 1960s provided another
analogy which split memory into two:
CPU/RAM = STS, STORAGE = LTS
Modal model of memory developed by Atkinson & Shiffrin (1968)
The modal model of memory
Sensory
Rehearsal
Store
Sensory
Store
Short
Long
Term
Term
Store
Store
Transfer
Sensory
Store
Displacement
(Forgetting)
But what is the evidence for separate STS / LTS?
Evidence for STS / LTS distinction
Converging evidence appeared to support the STS / LTS
distinction as proposed by the modal model:
• Capacity differences - STS = limited / LTS = unlimited
• Encoding differences - STS = phonological / LTS = semantic
• Serial Position Curves - STS = Recency / LTS = Primacy + Asym
• Forgetting - STS = trace decay / LTS = interference
• NP Evidence -
HM = intact STS, impaired LTS
KF = intact LTS, impaired STS
BUT - psychology is never simple...
Evidence for STS / LTS distinction
• Encoding differences - How do we comprehend text / learn
language / remember faces?
• SPCs - Recency effects after 20sec distraction following each
item (Tzeng, 1973). Long term recency (Baddeley & Hitch, 1977)
constant ratio rule (t / T) (Glenberg et al, 1980).
• Forgetting - Interference effects in STS (e.g. Release from
Proactive Interference - RPI)
• NP Evidence - Why is KF able to encode information in LTS if
the STS is a critical bottleneck?
The modal model provided the first systematic attempt to account for the
structures and processes which comprise the memory system
But by the end of the 1960s there were several well established findings that it
was unable to account for.
Baddeley and Hitch’s model of Working Memory
Articulatory loop
Central Executive
Background
By late 1960s - STS research “laboratory bound”
Modal model unable to account for important data:
1. Relationship between type of encoding and type of store
2. Why STM patients had normal LTM
3. Dual task data
Baddeley and Hitch - “What is the STS for?”
Assumed to be used for learning, reasoning and
comprehension - but little or no evidence.
Baddeley and Hitch developed dual task paradigms :-
Ss perform a primary task whilst simultaneously performing a
secondary task which is presumed to take up STS capacity.
Overt rehearsal of secondary task ensures that subjects are
not simply switching between tasks.
Dual Task Paradigms
Ss remember (and overtly rehearse) sequences of 0-8 digits
At the same time subjects perform a simple reasoning task
A precedes B:
AB (TRUE)
B is not preceded by A:
AB (FALSE)
Increase in reasoning time
is significant, but not large
(35%).
More importantly:
No effect on errors
Dual Task Paradigms
Primary task: learn a list of words
Secondary tasks:
1) copying pairs of digits
2) rehearsing 3 digit sequence
3) rehearsing 6 digit sequence
Condition 3 has a
small effect on
primary task
performance, but it
does not affect the
recency component of
the SPC.
The Phonological Loop
Dual task results imply system responsible for digit span
cannot be the same as system responsible for learning /
reasoning.
Baddeley and Hitch (1977) - performance on verbal span tasks
involved a speech-based system.
The phonological loop (AKA articulatory loop) comprises two
components:
Phonological Store: holds small amount of
speech based information
Articulatory Control
Process: Based on inner
Phonological
speech
Auditory
Presentation
Store
Visual
Presentation
Phonological Similarity Effect
Phonological similarity effect:
Recall of characters or words is impaired if they are
phonologically similar. (Conrad, 1964; Baddeley, 1966)
PVCGE is harder to recall than XRFYZ
This effect can be explained because items in phonological
store are based on phonological codes.
Neuropsychological Data
Modal model cannot explain data from STM patients such as
KF - LTM should also be impaired (STS is bottleneck)
Data can be explained if it is assumed that these patients have
impaired phonological stores.
Word Length Effect
Phonological
Span for shortsimilarity
words iseffect:
greater than span for long words.
Is this an effect of
syllables or
spoken duration?
E.g. is syllable a
“Unit of storage”?
Word Length Effect
Spoken duration appears to be crucial:
Memory spans are greater for words like “Bishop” and “Wicket”
than for “Harpoon” and “Labile” (Baddeley et al, 1975).
Language
Chinese
English
Welsh
Articulation Rate
265ms/digit
321ms/digit
385ms/digit
Digit Span
9.9
6.6
5.8
(Hoosain & Salili, 1988; Ellis & Hennelly, 1980)
Memory span and articulation rate are highly correlated in all
age groups - our span increases as we are able to articulate
more rapidly.
Overt or covert articulation serves to maintain items in the
phonological store by refreshing their fading traces. The faster
it can run, the longer the memory span.
Unattended Speech Effect
Performance on span tasks is impaired if items are
accompanied by other verbal material:
Colle & Welsh (1976) - immediate recall of digits is impaired if
accompanied by sound of someone reading German.
Explanation - unattended phonological material can gain
access to the phonological store.
Salame & Baddeley, (1987) - Spoken digits - “one”, “two”
impair digit span to the same degree as similar phonemes
like “tun, woo”
Both impair span more than non-similar words “happy, tipple”.
Explanation - code is phonemic, not semantic.
This suggests that listening to music with vocals may impair
your comprehension of complex texts.
Articulatory Suppression
The operation of the loop is disturbed if overt or covert
articulation of irrelevant items is performed. (Baddeley, 1984)
The word length effect is
abolished by articulatory
suppression.
Articulatory suppression
also removes
phonological similarity
effects, and unattended
speech effects
Explanation - articulation of irrelevant items dominates ACP Words cannot be “rehearsed” - word length has no influence.
What is the phonological loop for?
1. Learning to read:
Children with impaired reading ability have reduced memory
spans and have difficulties in tasks which require the
manipulation of phonological information (e.g. given Stop,
reply Top).
2. Language comprehension:
STM patients such as TB have some difficulty in
comprehending verbose or complex sentences e.g.
“The boys pick the apples” = OK; “The two boys pick the green
apples from the tree” = Impaired
3. Vocabulary acquisition
There is a strong correlation between non-word repetition
(which strongly taxes the phonological loop) and vocabulary
size (Gathercole & Baddeley, 1989)
The visuospatial sketch-pad
Baddeley - listening to American football disrupts driving
VSSP - A workspace in which an image can be stored and
manipulated to guide behaviour.
1
3
4
2
5
6
Brooks Matrix Task (1967)
Subjects told to imagine a 4x4 grid
Subjects learn sequence of
sentences:
Spatial: “In the next square to the
right put a 2”
Non-spatial: “In the next square to
the quick put a 2”
Subjects remembered 8 spatial vs 6 non-spatial.
Spatial instructions better when presented auditorily
Non-spatial instructions better when presented visually
The visuospatial sketch-pad
Baddeley et al, 1975 - Ss perform Brooks matrix task with and
without concurrent distractor - pursuit rotor.
Tracking disrupts the
spatial task, but not
its verbal equivalent:
Sketchpad relies on
spatial coding
Recent research has suggested that the VSSP be itself be
fractionated into separate visual and spatial components
(e.g. Pickering, 2001)
What is the sketchpad for?
Not as well studied as the articulatory loop.
• Geographical orientation: - learning our way around our
environment.
Planning and
performing
spatial tasks
• Hatano & Osawa (1983) -Japanese abacus experts
memory for numbers is disrupted by concurrent spatial but not
verbal task.
What is the sketchpad for?
(Eye Movement Desensitisation Reprocessing)
From the website: “What is EMDR”
“an innovative method of psychotherapy…The focus of EMDR treatment is the resolution of emotional
distress arising from difficult childhood experiences, or the recovery from the effects of critical
incidents, such as automobile accidents, assault, natural disasters, and combat trauma [PTSD]. Other
problems treated with EMDR are phobias, panic attacks, distress in children, and substance abuse.
Another innovative focus of EMDR is performance enhancement: which aims to improve the
functioning of people at work, in sports, and in performing arts”
“Therapy” used by people who should know better (Psychiatrists, Clinical
Psychologists etc), primarily in the treatment of PTSD.
Involves following the finger of therapist whilst imagining “negative
information identified with problem”
EMDR & VSSP
Most disabling symptom of PTSD is recurring, intrusive images
of precipitating trauma.
These images are presumably instantiated in VSSP
Effective volitional eye tracking involves the storage and
manipulation of both visual and spatial information
IN OTHER WORDS IT COMPETES FOR VSSP RESOURCES
Therefore EMDR is simply another “desensitisation” procedure
- of the type traditionally used by behavioural therapists.
Stickgold R (2002) EMDR: A putative neurobiological mechanism of action JOURNAL OF CLINICAL
PSYCHOLOGY 58 (1): 61-75
“We propose that the repetitive redirecting of attention in EMDR induces a neurobiological state, similar to that of
REM sleep, which is optimally configured to support the cortical integration of traumatic memories into general
semantic networks. We suggest that this integration can then lead to a reduction in the strength of hippocampally
mediated episodic memories of the traumatic event as well as the memories' associated, amygdala-dependent, negative
affect. Experimental data in support of this model are reviewed and possible tests of the model are suggested.”
McNally RJ (1999) EMDR and mesmerism: A comparative historical analysis J ANXIETY DISORD 13 (1-2): 225236 JAN-APR 1999
The Central Executive
• Most complex and least understood component of WM
• “In some ways the central executive functions more like an
attentional system than a memory store” - Baddeley (1997)
• “our initial specification of the CE was so vague as to serve
as little more than a ragbag…” Baddeley (1996).
• Model suggests CE coordinates the activity of the two slave
systems
• Other potential roles for the CE include coordinating
retrieval strategies, selective attention, temporary activation
of long term memory, suppression of habitual responses.
• Baddeley suggests that a model of action control developed
by Norman and Shallice (1980,1986) may serve as a model
of the central executive
Norman and Shallices (1986)
model of attentional control
Supervisory
Attentional
System
Perceptual
System
Trigger
Data
Base
Effector
System
Inhibition
Schema Control
Units
Contention
Scheduling
Evidence for the CE
Dual task performance and DAT:
• Pursuit rotor and digit span tasks were adjusted so that
individual performance was identical in DAT and matched
controls
• Combining the two tasks caused greater costs in the DAT
patients than the controls - CE impaired in DAT
Random number generation:
• Ss required to generate random sequences of letters make
more repetitions and stereotyped responses the faster the task
• Dominant schema (ABC, ITV etc) must be constantly
inhibited by the SAS and novel schema activated.
Evidence for the CE
Neuropsychological evidence: - Dysexcutive Syndrome
Original Norman and Shallice model developed to account for
behaviour of patients with frontal lobe lesions.
Perseveration - patients have lost ability to interrupt ongoing
schemas
Catatonia - patients can remain motionless and speechless for
hours - unable to initate schemas.
Distractibility - schemas easily “captured” by external/internal
stimuli
Utilisation behaviour - Lhermite (1983)
Problems for original WM model
1. Articulatory suppression:
According to the model, AS should prevent registration of
visual material (which must be recoded phonologically)
In fact, span only drops slightly (Baddeley et al, 1994)
2. Neuropsychological data:
STM patients, with digit spans of 2 or less, have visual spans
of about 4 (Baddeley et al, 1997).
3. Chunking:
If stimuli comprise a meaningful sentence, span is
considerably increased (e.g. info in LTM is used to chunk)
Problems for original WM model
4. Rehearsal
Not all rehearsal can be subvocal: How are items in VSS
rehearsed? What about children?
5. The role of consciousness
CE originally proposed to assist in binding - our ability to
integrate information about location, colour, size, smell, feel etc
of objects.
How could it do this without a multimodal short term store?
Baddeley (2000) suggests the above problems can be solved
by an Episodic Buffer.
A Revised WM Model
Central
Executive
Visual
Semantics
Episodic
LTM
Language
The Episodic Buffer
“A limited capacity temporary storage system that is capable of
integrating information from a variety of sources”
• Controlled by the CE
• Feeds information into and retrieves information from LTS
• Uses a common “multidimensional” code
The Episodic Buffer makes the link between Working Memory
and LTM more explicit
BUT:
Are VSS and AL still necessary?
Summary
• Original WM model was able to account for a considerable
body of data that the modal concept of an STS could not
explain.
• The concept of WM has proven to be enormously influential,
and is used by Neuroscientists, Neuropsychologists,
Psycholinguists and AI researchers.
• Problems with the original model led to the recent addition of
the Episodic Buffer
• The central executive component remains under-specified,
and controversial.