Short term working memory
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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

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Short-term working memory

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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

Short-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

Short-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

Short-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 were

    • 24 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?

Read aloud these digits

  • 41 64 00 40 11 49 2

Short-term memory

  • The next slide contains a series of digits. The digits are presented in groups. Read groups of digits aloud. Pause between each group. For example, suppose the digits were

    • 248 917 142 9123

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

Read aloud these digits

  • 416 400 401 1492

Short-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

Inducing 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

    • paradigm

      • study: 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

Inducing rapid forgetting

Inducing 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?

  • Inducing rapid forgetting

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

      • trace decay: automatic fading of memory

      • interference: memory is disrupted by other memory traces

        • proactive interference: effects of prior items on recall of subsequent items

        • retroactive interference: effects of subsequent items on recall of previous items

    Inducing 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

    Inducing 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

    Inducing rapid forgetting

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

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

    One 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

    Free Recall performance (Craik, 1970)

    Interpretation 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

    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

    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?

    Short-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

    Atkinson-Shiffrin model of memory











    Problems with modal model

    • 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 model

    • 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 model

    • 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 = 3

      • established 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


    • 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 selectively damaged

        • amnesics have damaged LTM component, but intact STM component

        • KF (and others) have damaged STM but intact LTM


    • 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

    Working memory model of Baddeley

    • 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

    • Experimental paradigm (dual task paradigm)

      • primary task: grammatical reasoning

        • Determine whether sentences are true/false

        • e.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

    Baddeley (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)

    Baddeley (1986)

    Other 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


    • 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

    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

    Baddeley’s working memory model





    Central Executive

    Working 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

    Working 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

    Visuo-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

    Central 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

    Central 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

    Central Executive

    • Vigilance

      • however, 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 performance

    • as 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

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

    • Overview

      • recently Baddeley updated the 3-component model of working memory

      • It proposes a 4th component, an episodic buffer

        • It has limited capacity

        • Stores information in a multimodal code

        • Binds information from subsidiary perceptual systems and LTM into episodic memory

        • Information is consciously retrieved

    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

    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 digits

        • One might expect recall to drop dramatically because Phonological loop is occupied and VSS is not very good at storing this type of information

    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 accounts

        • 1. Sentences are stored in PV’s LTM. Implausible because PV has normal LTM. Also amnesic px have normal memory span

    Episodic buffer of working memory

    • Possible accounts

      • 4. information is stored in an episodic memory buffer separate from LTM

        • Accounts for this result

        • Also 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

    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

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




    Episodic Buff


    Episodic LTM

    Properties of Model

    • See previous notes for description of

      • Central Executive Function

      • Phonological Loop

      • Visual spatial sketchpad

    Properties 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

    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

    A model of the Central ExecutiveSupervisory Attentional System SAS

    • Action slips

      • probably all of us have had the experience of performing some unintended action

        • e.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

    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

    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 place

      • research with damaged frontal lobe patients and monkeys suggests that performance is impaired if it requires

      • coordination of different elements of a complex activity

      • focused attention

      • focusing on the whole of a task

      • working on new situations

    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

    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. Response

      • Step 1. 18/2 = 9 (Clause 1)

      • Step 2. 18 x 2 = 36 (Clause 2)

    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













    SAS 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

    SAS 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)

    SAS 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

    SAS system

    • the process of routine selection between alternative actions is called contention scheduling; see Figure

      • e.g., light is orange and you are close to intersection, do you brake, accelerate, or maintain speed and continue through intersection

    SAS system

    • in addition, this model assumes that there is an additional system, the supervisory attentional system

      • this system has access to the environment and to the organism’s intentions

      • it does not directly control behavior, but instead modulates the lower level contention-scheduling system by activating or inhibiting particular schemata

    SAS 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.

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