Learning Center
Plans & pricing Sign in
Sign Out



									    Lecture 1: Short Term and Working Memory
•    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 be able to appreciate:

•    The importance of memory in our everyday lives
•    Why a distinction is made between short and long term
•    Evidence for the 3 original components of Baddeley’s model
     of Working Memory
•    Why the original model was revised
   Clive Wearing
Without our memories, what is left?

                QuickTime™ and a
         Sorenson Video decompressor
         are needed to see this picture.

      “Its exactly like death.”
          History of the STS/LTS distinction
1890 - William James draws distinction between primary and
secondary memory.


    Reward portion of present           Genuine past
          space of time
 Linked to conscious experience   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

                     Short                   Long
                      Term                   Term
                     Store                   Store
 Store             Displacement

  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 +
Asymp /

• 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.
                   Working Memory
“Courtney Young… was the undisputed Security Service
crossword king. He always claimed it was too easy to do the
Times crossword with a pencil. He claimed to do it in his head
instead. For a year I watched him do this, until finally I could
resist the temptation no longer. I challenged him, whereupon
he immediately wrote in each answer, without hesitation.”

Peter Wright, in Spy Catcher.

 (Quote used at beginning of chapter on Working Memory in Al Parkin’s text book)
Baddeley and Hitch’s model of Working Memory

                                  Articulatory loop

              Central Executive
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:
B is not preceded by A:

Increase in reasoning time
is significant, but not large

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 effect the
                                         recency component of
                                         the SPC.
         Evidence for the Phonological Loop
 Dual task results imply system responsible for digit span
 cannot be the same as system responsible for learning /
 Baddeley and Hitch (1977) - performance on verbal span tasks
 involved a speech-based system.
 The phonological loop (AKA articulatory loop) comprises two
               Phonological Store: holds small amount of
               speech based information
Articulatory Control
Process: Based on inner
speech                           Phonological          Auditory
           Visual                    Store             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.

PGCVE all have similar phonological codes.

Similar codes are harder to discriminate.

Hence recall is worse
                  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”?
                    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/digit                 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.
              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.
                       Patient Data
Learning to read
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.
To what extent does rehearsal depend on “inner speech”?
Dysarthria: Inability to use speech musculature due to brain
Dysarthric patients have normal digit spans, and show normal
phonological similarity effects:
Articulatory control processes do NOT depend on peripheral
speech musculature - we can run a motor program centrally.

SO: Phonological loop preferred to articulatory loop
        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. Vocab acquisition
There is a strong correlation between non-word repetition
(which strongly taxes the phonological loop) and vocabulary
size (Gathercole & Baddeley, 1989)
Imagery ignored by the behaviourists, - studied again in the

“Imagery debate” - Kosslyn and Pylyshyn

Are processes involved in imagery same as those involved in
visual perception?
Imagery = Analogue or Propositional ?

Debate proved rather barren - but generated interesting

Neuropsychological and neuroimaging data suggests neural
substrates involved in vision also involved in imagery.
              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.

                 3     4      Brooks Matrix Task (1967)
                              Subjects learn sequence of
          1      2     5      sentences:
                              Spatial: “In the next square to the
                       6      right put a 2”
                              Non-spatial: “In the next square to
                              the quick put a 2”1

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
             What is the sketchpad for?
Not as well studied as the articulatory loop
Geographical orientation: - learning our way around our

    Planning and
    spatial tasks

Hatano & Osawa (1983) -Japanese abacus experts memory
for numbers is disrupted by concurrent spatial but not verbal
                     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”
EMDR is a “Therapy” used by Psychotherapists, Psychiatrists, Clinical
Psychologists etc primarily for the treatment of PTSD.

Involves following the finger of therapist whilst imagining “negative
information identified with problem”

From the website: HOW DOES EMDR WORK?
“It is not clear how EMDR works because neuroscience researchers are still exploring how the brain
works... However, there is evidence for an innate information processing system that exists as part of
human thinking processes….”

“EMDR appears to produce a direct effect on the way the brain processes upsetting material.
Researchers have suggested that the eye movements trigger a neurophysiological mechanism that
activates an "accelerated information processing system." Accelerated information processing is a
phrase used in EMDR to describe the rapid working through, „metabolizing‟, of upsetting experiences.”

Stickgold R (2002) EMDR: A putative neurobiological mechanism of action JOURNAL OF CLINICAL
PSYCHOLOGY 58 (1): 61-75
…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 Psychology to the rescue…
McNally RJ (1999) EMDR and mesmerism: A comparative historical analysis J ANXIETY DISORD 13
(1-2): 225-236 JAN-APR 1999

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
Therefore EMDR is simply another “desensitisation” procedure
- of the type traditionally used by behavioural therapists.
Christman SD, Propper RE, Dion A. (2004) Increased interhemispheric interaction is associated with
decreased false memories in a verbal converging semantic associates paradigm. Brain Cogn. 56:313-9.
                 The Central Executive
Most complex and least understood component of WM model

“In some ways the central executive functions more like an
attentional system than a memory store” - Baddeley

Model suggests CE coordinates the activity of the two slave

Other potential roles for the CE include coordinating retrieval
strategies, and selective attention
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


Perceptual                                        Effector
 System                                           System

                                              Schema Control
              Inhibition                          Units
                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
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
Catatonia - patients can remain motionless and speechless for
hours - unable to initate schemas.

Distractibility - schemas easily “captured” by external/internal

Utilisation behaviour - Lhermite (1983)
              Utilisation Behaviour
Utilisation behaviour:
The tendency to grasp common objects when presented, and
perform the function commonly associated with the object
E.g 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


 Visual          Episodic
Semantics         LTM
                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


Are VSS and AL still necessary?
• Original 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, and AI

• Problems with the original model led to the addition of the
Episodic Buffer

• The central executive component remains under-specified,
and controversial.

To top