Lecture 1: Short Term and Working Memory Outline

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Lecture 1 Short Term and Working MemoryOutline

• What is memory?
• The Short Term / Long Term distinction
• Baddeleys model of Working Memory
• Evidence for Baddeleys model
• The episodic buffer
• By the end of the lecture you should have
  learned
• Why a distinction is made between short and long
  term memory
• Key experiments that provide evidence for the 3
  original components of Baddeleys model of
  Working Memory
• Why the original model was revised

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History of the STS/LTS distinction
1890 - William James draws distinction between
primary and secondary memory.
SECONDARY MEMORY
PRIMARY MEMORY
Reward portion of present space of time
Genuine past
Unconscious - permanent
Linked to conscious experience
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)
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The modal model of memory
But what is the evidence for separate STS / LTS?
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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...

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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.

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Baddeley and Hitchs model of Working Memory
Articulatory loop
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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.
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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
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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.
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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
Articulatory Control Process Based on inner
speech
Auditory Presentation
Visual Presentation
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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.
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Word Length Effect
Phonological similarity effect
Span for short words is greater than span for
long words.
Is this an effect of syllables or spoken
duration? E.g. is syllable a Unit of storage?
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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 Articulation Rate Digit
Span Chinese 265ms/digit 9.9 English 321ms/digi
t 6.6 Welsh 385ms/digit 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.
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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.
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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.
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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)
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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.
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
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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)
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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.

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What is the sketchpad for?
(Eye Movement Desensitisation Reprocessing) From
the website What is EMDR an innovative
method of psychotherapyThe 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
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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) 225-236 JAN-APR 1999
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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

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Norman and Shallices (1986) model of attentional
control
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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.

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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)
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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)
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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.
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A Revised WM Model
Central Executive
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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?

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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.