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Short-term working memory Students of memory (e.g., James, Galton) have long considered that there is a memory system that keeps in consciousness a small number of ideas William James referred to this system as primary memory the primary memory is probably more closely related to working memory than to STM; this model will be discussed later on today

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Short-term working memory. Students of memory (e.g., James, Galton) have long considered that there is a memory system that keeps in consciousness a small number of ideas William James referred to this system as primary memory - PowerPoint PPT Presentation

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Page 1: Short-term working memory

Short-term working memoryShort-term working memory

• Students of memory (e.g., James, Galton) have long considered that there is a memory system that keeps in consciousness a small number of ideas

• William James referred to this system as primary memory

• the primary memory is probably more closely related to working memory than to STM; this model will be discussed later on today

Page 2: Short-term working memory

Short-term working memoryShort-term working memory

• The capacity of short-term memory is traditionally measured using a memory-span procedure

• in this procedure a participant is presented a sequence of items, and is required to repeat them back; start with one item, increasing the number of items by 1 until the participant begins to make mistakes

Page 3: Short-term working memory

Short-term working memoryShort-term working memory

• the point at which the participant is able to recall all items correctly 50% of the time is designated as her/his memory span

• factors affecting memory span– auditory presentation leads to larger memory

span estimates than visual presentation– rhythmic presentation is better than non-rhythmic

presentation

Page 4: Short-term working memory

Short-term memoryShort-term memory

– The next slide contains a series of digits. The digits are presented in pairs. Read the pairs of digits rhythmically aloud. Pause between each pair. For example, suppose the digits were24 89 17 14 29 12 3

– After you have read the pairs aloud, I want you to write down as many digits as you can remember. Any questions?

Page 5: Short-term working memory

Short-term memoryShort-term memory

– Write down as many digits as you can remember.

Page 6: Short-term working memory

Read aloud these digitsRead aloud these digits

• 41 64 00 40 11 49 2

Page 7: Short-term working memory

Short-term memoryShort-term memory

– Write down as many digits as you can remember.

Page 8: Short-term working memory

Read aloud these digitsRead aloud these digits

• 416 400 401 1492

Page 9: Short-term working memory

Short-term memoryShort-term memory

– Write down as many digits as you can remember.

Page 10: Short-term working memory

Short-term working memoryShort-term working memory

• factors affecting memory span (cont’d)– recoding or chunking information; George Miller

showed in his classic paper (1956) that memory span is determined by the number of ‘chunks’ or integrated items you need to recall, not the number of items presented

Page 11: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

• Brown-Peterson paradigm– Brown (1958) and Peterson & Peterson (1959)

showed that it is possible to induce very rapid forgetting if you distract person

– paradigmstudy: present a small number of items followed by

a number such as 632. Participant is required to count backward by threes until given a recall signal. Then he/she attempts to recall studied items

Page 12: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

Peterson & Peterson (1958) Recall of three consonants

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Page 13: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

Note: Murdock (1961) showed that performance is about the same for 3 consonants as it is for 3 words, illustrating the importance of chunking

– why is information forgotten in the Brown-Peterson paradigm?

Page 14: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

• why is information forgotten in the Brown-Peterson paradigm?– trace decay: automatic fading of memory– interference: memory is disrupted by other

memory tracesproactive interference: effects of prior items on

recall of subsequent itemsretroactive interference: effects of subsequent

items on recall of previous items

Page 15: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

• why is information forgotten in the Brown-Peterson paradigm?– Petersons argued that it must be trace decay; it

couldn’t be retroactive interference because numbers are very different from consonants

– Keppel & Underwood (1962) showed that proactive interference seemed to be responsible because if performance on the first trial only is examined there is little decline in performance over the retention interval

Page 16: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

• Further evidence for the importance of proactive interference (PI)– release from PI– numerous studies have established that if you

present several lists of items using a Brown-Peterson procedure (Study: present list of 3 items; count backwards by 3s for 15 sec, then attempt recall of the studied items. Results show that performance declines across lists

Page 17: Short-term working memory

Inducing rapid forgettingInducing rapid forgetting

• Results show that performance declines across lists (build up of PI)

• If you change categories, then performance increases (release from PI)

Page 18: Short-term working memory

One or two memory systemsOne or two memory systems

• The theoretical question underlying much of this research had to do with whether there was evidence for the STM/LTM distinction

• One approach to investigating this question involves determining whether certain tasks have separable components

• One task is free recall

Page 19: Short-term working memory

Free Recall performance (Craik, 1970)

Free Recall performance (Craik, 1970)

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Page 20: Short-term working memory

Interpretation of free recall studyInterpretation of free recall study

Primacy and intermediate components of the serial position curve are lower in the delayed compared to immediate condition; recency portion of the curve is differentially lower in the delayed condition

interpretation: delayed condition has a stronger influence on recency portion of curve because recency reflects STM performance

Page 21: Short-term working memory

Neuropsychological Evidence for separation of STM and LTM

Neuropsychological Evidence for separation of STM and LTM

Data from amnesics support the viability of the distinction between STM and LTM because amnesics have normal digit span, which is mediated by STM, but are impaired in their ability to acquire and retain LTM memories

Page 22: Short-term working memory

Neuropsychological Evidence for separation of STM and LTM

Neuropsychological Evidence for separation of STM and LTM

Free recall data in amnesics also supports this distinction. Given your understanding of free recall I want you to predict performance of amnesics (Baddeley & Warrington, 1970) In immediate free recall, how should amnesics

perform on the recency portion of the curve? What about the primacy portion of the curve?

Page 23: Short-term working memory

Short-term working memoryShort-term working memory

• Atkinson-Shiffrin model of memory (1968)– distinguishes between two types of memory: short-term

and long-term memory– short-term memory (STM): a temporary storage system

capable of holding a small amount of information (e.g., telephone number)

– information in STM is forgotten quickly unless it is rehearsed or transferred into LTM

– Long-term memory (LTM): a permanent memory store with no capacity limitations

Page 24: Short-term working memory

Atkinson-Shiffrin ModelAtkinson-Shiffrin Model

(Atkinson & Shiffrin, 1968)

Page 25: Short-term working memory

• Modal model assumes that STS plays a critical role in the transfer of information into LTS– Specifically, this model suggests that the

capacity of the STS should determine the probability that an item enters LTS and

– The amount of exposure in STS should affect the likelihood that an item enters into LTS

Problems with modal modelProblems with modal model

Page 26: Short-term working memory

• Both these implications are incorrect– several studies have shown that under some

conditions the number of times material is rehearsed is a poor predictor that it will be recalled subsequently (shallow rehearsal)

Problems with modal modelProblems with modal model

Page 27: Short-term working memory

– Shallice and Warrington (1970) and others have established that at least some people with poor memory span (this suggests that STS is damaged) have normal long-term memory KF memory span WAIS score = 2, Mean = 10,

Standard deviation = 3established that KF understood spoken words by

presenting a list of spoken words; task was to tap table when words were from a given category

KF also was impaired when RN STM test administered

Problems with modal modelProblems with modal model

Page 28: Short-term working memory

• Evidence supporting STM vs LTM distinction– tasks such as free recall seem to have both STM

and LTM components– Neuropsychological evidence suggests that both

components can be damagedamnesics have damaged LTM component, but

intact STM componentKF (and others) have damaged STM but intact LTM

SummarySummary

Page 29: Short-term working memory

• However, the modal model (Atkinson-Shiffrin) does have problems accounting for– the finding that patients with STM deficits appear

to have intact LTM– maintaining an item in STM does not ensure its

transfer to LTM

SummarySummary

Page 30: Short-term working memory

• Baddeley’s early work focused on testing the hypothesis that STS is important because it acts as a working memory, a system that is important for holding and manipulating information, and it is needed for a broad range of cognitive tasks

Working memory model of Baddeley

Working memory model of Baddeley

Page 31: Short-term working memory

• Experimental paradigm (dual task paradigm)– primary task: grammatical reasoning

Determine whether sentences are true/falsee.g., A follows B -- BA (true)e.g., B is not preceded by A - AB (false)

– secondary task: concurrent digit task: remember number sequences ranging in length from 0 to 8

Working memory model of Baddeley

Working memory model of Baddeley

Page 32: Short-term working memory

Baddeley (1986) cont’dBaddeley (1986) cont’d

• Results– as shown in the accompanying figure, reasoning

time increased with concurrent digit load. However, performance remained high, and errors remained low (about 4% and did not vary with digit load)

– thus, overall performance remains quite good, even when the overall digit load is 8 (memory span capacity)

Page 33: Short-term working memory

Baddeley (1986)Baddeley (1986)

Speed of reasoning by concurrent digit load

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Page 34: Short-term working memory

Other important resultsOther important results

• Baddeley, Lewis, Eldridge, & Thomson (1984) showed that:

a concurrent digit span task had a strong effect on encoding and remembering new material

however, it had no effect on accuracy of performance when the concurrent digit span task was performed during retrieval (although retrieval latency was slowed)

this suggests that the system responsible for holding digits does not play a critical role in retrieval as suggested by previous models of memory

Page 35: Short-term working memory

ConclusionsConclusions

• These findings and others are difficult to reconcile with a model in which overloading the short-term store leads to a complete breakdown of performance on the primary task

Page 36: Short-term working memory

Working memory model of Baddeley

Working memory model of Baddeley

– Baddeley proposed to account for these results by postulating that the digit span limitations are set by one system, leaving other components of working memory relatively unimpaired

– Basic model of working memory consists of a controlling attentional system (called the central executive) and two slave systems, an articulatory or phonological loop system and a visuo-spatial sketch pad

Page 37: Short-term working memory

Baddeley’s working memory model

Baddeley’s working memory model

Central Executive

Visuo-spatialsketchpad

Phonologicalloop

Page 38: Short-term working memory

Working memoryWorking memory

• Phonological loop characteristics– consists of a phonological store (codes speech-

based information), and maintains information for about 2 seconds

– articulatory control process that refreshes items in store by means of subvocal rehearsal

Page 39: Short-term working memory

Working memoryWorking memory

• Phonological loop– appears to play an important role in reading

poor readers tend to have poor short-term memory span

– also appears to play a role in the comprehension of language and in the acquisition of vocabulary

Page 40: Short-term working memory

Visuo-spatial sketchpadVisuo-spatial sketchpad

• Information can enter the sketchpad visually or through the generation of a visual image

• access to this store by visual information is obligatory

• the information in this store may be visual or spatial or both

Page 41: Short-term working memory

Central ExecutiveCentral Executive

• The central executive plays an important role in controlling attention. Our discussion of the central executive will begin with a discussion of the interplay of attention and memory

Page 42: Short-term working memory

Brain and working memoryBrain and working memory

– Psychological theory and data suggest that there is an important distinction between maintaining information in consciousness (James, Galton, Miller idea) and manipulating information (Baddeley idea)

Page 43: Short-term working memory

Brain and working memoryBrain and working memory

– Neuroimaging data suggest dorsal regions of prefrontal cortex (PFC) necessary manipulation in addition to maintenance, whereas ventral PFC needed for maintenance

– Conclusion different cognitive processes are mediated by different brain regions, consistent with psych data

Page 44: Short-term working memory

Brain and working memoryBrain and working memory

– Different pattern of findings has been obtained from neural brain region recordings of monkeys

– This research showed that dorsal regions of PFC were activated for spatial memory, whereas ventral regions of PFC were specialized for object working memory

– Conclusion: this finding suggests that brain regions are organized on the basis of the content of information being processed

– Issue is not yet resolved

Page 45: Short-term working memory

Central ExecutiveCentral Executive

• Vigilance– recall vigilance refers to sustained attention

Parasuraman (1979) showed that vigilance performance decreases if the vigilance task has a short-term memory component involving storage and manipulation of information. For example, if the participant has to detect three consecutive odd numbers from a stream of digits or must judge whether adjacent items are of the same hue, performance declines

Page 46: Short-term working memory

Central ExecutiveCentral Executive

• Vigilancehowever, if the participant must evaluate each

item on its own (e.g., detect whether a product such as a frying pan) has flaws, then performance tends to remain stable

• Dual task performanceas discussed in a prior lecture, it is difficult to

perform two tasks at the same time. However, the degree of difficulty depends upon the tasks being performed and the expertise of the person

Page 47: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS• Norman and Shallice developed a model of

the control of action called the Supervisory Attentional System – this model was developed by considering our

knowledge of action slips and frontal lobe function

Page 48: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS• Action slips

– probably all of us have had the experience of performing some unintended actione.g., driving home from York in your car and forgetting to

make a detour to pick up your clothes from the dry cleaners

e.g., William James… going upstairs and ending up in bed

Reason (1979) has studied action slips and showed that these errors tend to occur when you are pre-occupied with some other thought

Page 49: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS• Action slips are actions that are inappropriate

for the goals of the participant. However, the actions themselves are meaningful, and reasonably well performed– my driving is safe, I obey traffic rules etc.

• This suggests that some actions, once they are initiated, can be accurately performed with little conscious attention being paid to them

Page 50: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS– Other actions and other types of behaviour seem to

require a central system and performance declines if such a system is not in placeresearch with damaged frontal lobe patients and

monkeys suggests that performance is impaired if it requires

coordination of different elements of a complex activityfocused attentionfocusing on the whole of a taskworking on new situations

Page 51: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS– It is well established that patients with frontal lobe

damage may have relatively intact performance on IQ tests

– Luria (1966) proposed that the frontal lobes are involved in programming, regulation, and verification of activity

Page 52: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS– Sample problem given to pt with frontal damage

There were 18 books on two shelves, and there were twice as many books on one shelf than on the other. How many books were on each shelf?

Pt. ResponseStep 1. 18/2 = 9 (Clause 1)Step 2. 18 x 2 = 36 (Clause 2)

Page 53: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS• Sample problem 2

– Bat and ball cost $1.20– Bat costs $1.00 more than ball– How much does the bat cost?

Page 54: Short-term working memory

A model of the Central ExecutiveSupervisory Attentional System

SAS

A model of the Central ExecutiveSupervisory Attentional System

SAS– For problems such as these Shallice, Norman,

and others have proposed that a central executive is needed

– their model is presented in the next slide

Page 55: Short-term working memory

PerceptualStructures

TriggerDataBase

EffectorSystem

ContentionScheduling

SupervisoryAttentional

System

Page 56: Short-term working memory

SAS systemSAS system

• According to this system routine actions run off relatively automatically– perceptual information comes into the system

and it makes contact with stored information and that information triggers certain responses. These responses eventually result in actions that are produced by the effector system

– e.g., walking on a country road

Page 57: Short-term working memory

SAS systemSAS system

• At any given moment this model postulates that our behaviour is controlled by schemata, that control lower-level programs– for example the schema that controls our driving

requires visual spatial and motor control systems, and may call particular component schema in well-defined circumstances (e.g., if light turns orange, and you are well away from the intersection, start braking)

Page 58: Short-term working memory

SAS systemSAS system

– schemata are assumed to be activated by triggering inputs, and to be selected if the level of activation exceeds a threshold

– they also tend to be mutually inhibitory– once a schema is selected, the component schema

associated with a given schema become activated (e.g., component schema for braking, turning on lights, windshields etc.)

– the process of routine selection between alternative actions is called contention scheduling

Page 59: Short-term working memory

SAS systemSAS system

– the process of routine selection between alternative actions is called contention scheduling; see Figuree.g., light is orange and you are close to

intersection, do you brake, accelerate, or maintain speed and continue through intersection

Page 60: Short-term working memory

SAS systemSAS system

– in addition, this model assumes that there is an additional system, the supervisory attentional systemthis system has access to the environment and to

the organism’s intentionsit does not directly control behavior, but instead

modulates the lower level contention-scheduling system by activating or inhibiting particular schemata

Page 61: Short-term working memory

SAS systemSAS system

– the supervisory attentional system is involved in initiating willed actions, and in working in situations in which routine actions are not satisfactory--e.g., dealing with novelty, overcoming temptation, etc.

Page 62: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Overview– This article updates Baddeley’s 3-component

model of working memory– It proposes a 4th component, an episodic buffer

It has limited capacityStores information in a multimodal codeBinds information from subsidiary perceptual

systems and LTM into episodic memoryInformation is consciously retrieved

Page 63: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Background– 3 component model of working memory consists

of central executive and two slave systems, the phonological loop and the visuo-spatial sketchpad

– Central executive is an attention controller– Phonological loop stores speech-based info– Visuospatial sketchpad stores visual info

Page 64: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Problems with 3-component model of WM– Articulatory suppression

Saying ‘the’ repetitively (occupying the phonological loop) does not have a devastating effect on recall of visually presented numbers

Recall drops from 7 to 5 digitsOne might expect recall to drop dramatically

because Phonological loop is occupied and VSS is not very good at storing this type of information

Page 65: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Problems with 3-component model of WM– Prose recall of a patient (PV) with word-span of 1

word is 5 words. This is less than the span of 15 words, but much more than 1 words

– Possible accounts1. Sentences are stored in PV’s LTM. Implausible

because PV has normal LTM. Also amnesic px have normal memory span

Page 66: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Possible accounts– 2. PV stores information in phonological loop

Implausible because her capacity is 1 word

Page 67: Short-term working memory

Episodic buffer of working memory (Baddeley’s new model)

Episodic buffer of working memory (Baddeley’s new model)

• Possible accounts– 3. Already existing information in LTM is

activatedImplausible because such a system could not

store novel information

Page 68: Short-term working memory

Episodic buffer of working memory

Episodic buffer of working memory

• Possible accounts– 4. information is stored in an episodic memory buffer

separate from LTMAccounts for this resultAlso accounts for finding that amnesics can retain relatively

large amounts of complex information briefly (e.g., sentence span, info about a bridge game)

People integrate information across modalities (note: may be two types of integration; automatic and controlled; episodic integration is controlled integration); see binding problem discussion

Page 69: Short-term working memory

Episodic buffer of working memory

Episodic buffer of working memory

• Binding problem– Information that is processed independently by separate

cognitive processes must be bound together because our experience of the world (and our memory of it as well) is coherent

– People can also retrieve information about an episode when give part of an episode (e.g., given a spatial cue, state what object was stored there)

– Episodic buffer is one way in which the binding problem can be solved

Page 70: Short-term working memory

4-component model of WM (see Fig.1)

4-component model of WM (see Fig.1)

visspat Episodic Buff Phon.

CentralExec

Episodic LTM

Page 71: Short-term working memory

Properties of ModelProperties of Model

• See previous notes for description of – Central Executive Function– Phonological Loop– Visual spatial sketchpad

Page 72: Short-term working memory

Properties of ModelProperties of Model

• Episodic buffer– Integrates information across modalities and

from different sources– Integrates information across time– Has limited capacity– Is capable of manipulating information– Is consciously accessible from Central

Executive