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Working Memory

Chapter 4

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Working Memory

Some memories are very fragile and go into oblivion very quickly. Working memory is one such memory.

1. Try this. Do this mentally. Write your answers on paper.

a. 7 X 9 =

b. 74 X 9 =

c. 74 X 96 =

63

666

7104

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Working Memory (WM)

1. We know attention is limited. So information that gets to memory is also limited. Thus capacity of working memory is limited.

2. Working memory is brief, immediate memory we use for current information. A portion of working memory coordinates ongoing mental activities.

3. Working memory has been known as short-term memory, and is contrasted from long-term. Some investigators believe the two are the same (Nairne, 2002).

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Classic Research on Working Memory

(Short-term Memory)

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Short-term Memory

In the 19th century, Sir George Hamilton discovered that he could accurately store about 7 items

(marbles) in memory if he glanced at the items quickly. If the items were more than 7 his accuracy

decreased.

Sir George Hamilton

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Short-term Memory

George Miller

1. Miller (1956) wrote, “The magical number seven plus or minus two: some limits on our capacity for processing information”.

2. Miller suggested that the capacity of our short-term memory was small. We could store about 5-9 items in it.

3. He also showed that items could be “chunked”, which would increase our memory capacity.

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Try This !

R E C A L L !

C T A I I L T C S F R O

R E C A L L !

F R A C T O L I S T I C

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Another Example

870 + 230 + 5 3 3 9

(1) (1) (4)

Capacity of short-term memory may be increased by a process called “chunking”.

870-230-5339 (10 items)

2 chunks + 4 items (6 items)

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Miller’s Memory

Miller thus conceived of short-term memory as a passive store capable of holding 7±2 items or chunks.

Working Memory

7

5

870

apple

1876

P

water

3

Z

4

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Short-term Memory: Duration

Brown (1958) Peterson and Peterson (1959) used blocking of rehearsal to measure the duration of

short-term memory.

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Short-term Memory: Duration

These experiments suggested that duration of information in short-term memory stays for about

18 seconds and then decays, unless rehearsed.

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0 3 6 9 12 15 18

Pe

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Time Delay (Seconds)

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Recency Effect

1. Short-term memory (and long-term memory) have been studied through serial position effect procedures, which generate a U-shaped curve.

2. When a list of items are recalled, items at the beginning of the list and at the end of list are recalled more than the items in the middle. This is called the serial position effect.

3. Recall of beginning items refers to primacy effect and the items recalled at the end of the list refer to recency effect.

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Recency Effect

4. Recency effect can also determine the capacity of short-term memory.

Short-termMemory

RecencyEffect

PrimacyEffect

14 apple

15 jet

16 groom

17 pair

18 blue

19 pride

20 water

13 car

12 dizzy

List

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Model of Memory

1. Based on experiments like serial position effect Atkins and Shiffrin (1968) proposed two separate stores for short-term (recency effect) and long-term (primacy effect) memories.

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Model of Memory

2. Atkins and Shiffrin (1968) also suggested that control processes like rehearsal could improve short-term memory.

3. With recent advancements by Alan Baddeley our way of looking at short-term memory has changed. In fact the name short-term memory has changed to working memory.

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Factors Affecting Working Memory

1. Capacity of working memory may be affected by the length of the items on the list. If each item on the list was short (single syllable) it would take less time to pronounce it.

2. Memory capacity improved with shorter pronunciation time than when it was longer.

Short Pronunciation Long Pronunciation

Burma Switzerland

China Nicaragua

Greece Afghanistan

Cuba Philippines

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Pronunciation Time

3. The most through study on pronunciation time on the capacity of shot-term memory was carried out by Naveh-Benjamin and Ayres (1986).

4. The investigators took numbers in four languages and looked at memory spans.

5. Since number in English and Spanish were shorter than Hebrew and Arabic. Capacity of memory spans were greater in former than latter languages.

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Syllable Length

No. English Spanish Hebrew Arabic

1 One Uno Eh'ad Wa’hid

2 Two Duo Shnyim Ith’n’an

3 Three Tres Shlosha Tha’la’tha

4 Four Cuatro Arba'a arba’a

5 Five Cinco H'amisha Kham’sa

6 Six Seis Shisha Sit’ta

7 Seven Siete Shiv'a sab’a

8 Eight Ocho Shmona Tha’ma’niya

9 Nine Nueve Tish'a tis’a

10 Ten Diez Assara ‘ashra

Syl 1.0 1.6 1.9 2.4

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Memory Span

5.0

6.0

7.0

8.0

English Spanish Hebrew Arabic

1.0 1.6 1.9 2.4

Mean Syllable per Digit

Mem

ory

Sp

an

Results clearly show that as the pronunciation time increases the memory span decreases.

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Proactive Interference

1. Meaningfulness of words can have important affect on capacity of working memory.

2. Wickens and colleagues (1976) used proactive interference and release from it to show how capacity of memory can increase.

3. Proactive interference involves having trouble learning new material because older material interferes, especially if the material to be learnt is the same or similar.

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Proactive Interference: Release

4. However, there can be release from proactive interference when new material is different from older material.

5. Wickens and colleagues (1976) used 5 semantic categories, fruits, vegetables, flowers, meats, and occupations as new material to be learnt when the original category was fruits.

6. Results showed a consistent release from proactive interference as the categories became more and more dissimilar.

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Semantic Similarity

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1 2 3 4

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Occupations

Meats

Flowers

Vegetable

Fruit

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Working Memory Approach

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Non-unitary Nature of Working Memory

1. What caused Baddeley to suggest that working memory is not unitary?

2. Baddeley and Hitch (1974) gave participants random numbers 0-8 digits long to rehearse in order, and also gave them spatial reasoning task to perform. Showed BA, and then a statement Afollows B. Answer yes.

3. Simultaneously doing reasoning task did not increase errors on recall of random numbers. Suggesting that working memory had multiple parts, with overall larger capacity as envisioned by Miller.

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Model of Working Memory

Baddeley (2006) final division of working memory consisted of the following components.

VisuospatialSketchpad

EpisodicBuffer

PhonologicalLoop

PhonologicalLoop

EpisodicBuffer

VisuospatialSketchpad

CentralExecutive

WorkingMemory

Long-termMemory

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Phonological Loop

PhonologicalLoop

WorkingMemory

Rehearsal

1. Many studies proposed that phonological loop was acoustical in nature.

2. And involved rehearsing verbal material in this acoustical form.

3. If verbal material is acoustical in form then many errors in working memory can be based on acoustical confusions.

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Acoustical Confusions

4. Wickelgren (1965) showed that acoustical confusions lead to errors when similar sounding letters and numbers were recalled.

Lists Errors Recall

4 N F 9 G 4

B 3 0 R 2 P, E, V, D, 3 P

5 A 7 6 E 5

6 8 C Z 8 6

Y 2 4 K L Y

3 K N 2 D C, E, V, D, B C

N Q 5 H 1 N

T 1 C 5 7 T

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Acoustical Confusions

5. Kintch and Buschke (1969) showed that homonyms cause similar acoustic confusions. When asked to recall the word after the word so(sounds like sew) the participants erred in recalling tax. Recall Error Recall

Tacks

So Sew

Buy Buy

Owe

Tied

Sew So

Tax Tax

By

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Division of Phonological Loop

Gathercole & Baddeley (1993) have recently suggested that phonological loop could be further

subdivided into two parts.

PhonologicalStore

WorkingMemory

Sub-vocalRehearsalProcess

Phonological Loop

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Biology of Phonological Loop

Recent studies have suggested that phonological loop resides in left hemisphere. The phonological

store resides in parietal cortex and sub-vocal rehearsal process in the frontal cortex.

ParietalCortexFrontal

Cortex

LeftHemisphere

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Visuospatial Sketchpad

1. A division of working memory that generates and stores visual and spatial information.

2. Visuospatial sketchpad stores information about a visual scene and lets us navigate through it.

3. The sketchpad stores a coherent picture of objects in the scene and their relative position in it.

VisuospatialSketchpad

WorkingMemory

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Visuospatial Sketchpad

4. It stores visual information processed by verbal stimuli. Visualization or imagining related stories.

5. Visuospatial sketchpad also has limited capacity, like the phonological loop. To much information in the store makes it difficult to accurately recover the information.

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Visuospatial Sketchpad: Research

1. Perceptual processes and processes that require imagination cannot be carried simultaneously (Baddeley, 1999; 2006).

2. There is not a lot of research carried out on the visuospatial sketchpad:

a. No standard visual stimuli like letter or words for verbal tests.

b. People tend to respond to visual stimuli by giving them names.

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Visuospatial Sketchpad: Uses

1. The sketchpad is useful for people in engineering and architectural disciplines.

2. Sketchpad retains images thus we can interact with environment using our imagination.

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Visuospatial Sketchpad: Neurobiology

1. Visual and spatial information are processed in the right hemisphere.

2. Visual, frontal and parietal cortices are involved with processing visuospatial information for working memory

ParietalCortex

FrontalCortex

VisualCortex Right

Hemisphere

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Central Executive

The central executive integrates information from the phonological loop, visuospatial sketchpad,

episodic buffer and long-term memory.

VisuospatialSketchpad

EpisodicBuffer

PhonologicalLoop

PhonologicalLoop

EpisodicBuffer

VisuospatialSketchpad

CentralExecutive

WorkingMemory

Long-termMemory

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Central Executive : Characteristics

1. The central executive itself is not a memory store, but works like a CEO decides on a number of executive functions.

2. Decides on issues that are important and attends to them, giving less attention to non-important issues.

3. Gathers information from many sources, including phonological loop, visuospatialsketchpad, episodic buffer and long term memory to make such decisions.

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Central Executive: Characteristics

4. Limited ability to perform simultaneous tasks. Cannot make many decisions at the same time.

5. Selects strategies and figures out how to tackle a problem.

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Central Executive & Daydreaming

1. Central executive engages in strategies to tackle problems faced by working memory.

2. In some cases these strategies fail. Teasdale and colleagues (1995), asked participants to generate a random number list using 1 through 10 numbers for 5 minutes, producing each number a second.

3. The task became difficult and the individual starts to have stimulus independent thoughts (SITs) or daydreams.

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Central Executive & Daydreaming

4. During SITs the random number list does not remain very random, suggesting that the central executive ability to do simultaneous tasks is compromised.

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Central Executive: Neurobiology

The biology of the central executive is little understood. Investigators have suggested, based on imaging studies, that Dorsolateral Prefrontal Cortex

(DPFC) is active when people engage in central executive tasks.

DorsolateralPrefrontal

Cortex (DFPC)

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Episodic Buffer

1. After 25 years of research and investigations Baddeley proposed the fourth component of working memory, episodic buffer.

2. Episodic buffer fourth component of the working memory and holds information about episodes that take place in our personal life.

EpisodicBuffer

WorkingMemory

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Episodic Buffer

3. The capacity of episodic buffer is small.

4. Contents in episodic buffer can be combined from phonological loop (verbal), visuospatialsketchpad (visual-spatial) and long-term memory.

5. Because episodic buffer is new little is known about it.

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Depression & Working Memory

1. Depression is a common psychological disorder affecting 10-15% of people at any one point in their life (US data).

2. Depressive conditions includes: sadness, hopelessness, feeling fatigue, no interest in leisure activities.

3. So it is important to consider depression and its affects on working memory.

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Depression & Working Memory

4. Christopher and McDonald (2005) looked at a number of measures for working memory in depressed patients.

Working Memory Depressed Patient Normal

Phonological Loop

3.4 letters 5.3 letters*

Visuospatial Sketchpad

Mean Span 6.7 Mean Span 7.8*

Central ExecutiveSpan letters 2.8Span String 3.2

Span letters 4.9*Span strings 7.4*

* All significant differences

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Timeline of Working Memory

1. Short-term memory (1950-60) presented a rigid limited and passive form of memory, radically changed by Baddeley to what we now as working memory.

2. Research on working memory during 1970-90 focused on phonological loop, visuospatialsketchpad, and central executive.

3. From 1990 onwards discovery of episodic buffer, and research on it has been on the forefront of investigations in working memory.