4 icwm 2004

The time-based resource-sharingmodel

of working memory

Pierre Barrouillet

Valérie CamosUniversité de Bourgogne

LEAD - CNRS

How does working memory work ?

• How is the relevant information maintained active during processing ?

• What is the nature of the resource to be shared ?

• How is this sharing achieved ?

• What are the limiting factors of WM functioning ?

Time-Based Resource-Sharing ModelThe main proposals

Barrouillet, Bernardin, & Camos, JEP:G, 2004

1. Processing and maintenance require attention which is a limited resource (some sharing is needed)

2. As soon as attention is switched away, activation suffers from a time-related decay

3. Among attention demanding activities, retrievals from memory should have the most detrimental effect on concurrent maintenance

4. When processing involves retrievals, sharing attention is time based because a central bottleneck allows only one retrieval at a time

Activation is attention demanding

1. Processing and storage require attention

Processing Maintenance

Retrievals of declarative knowledge stored in long-term

memory

Frequent refreshment of decaying traces of the to-be-

maintained items

STM = Activated part of LTMProductions rules read and update the content of WM

Anderson’s ACT-R Framework

Activation of memory items

2. When attention is switched away, activation suffers from a time-related decay

• Activation is produced by attentional focusing (Cowan, 1995).

• Activation declines as soon as the focus of attention is switched away.

• While processing captures attention, relevant information declines in STM

• When attention is used to refresh decaying memory traces, processing is temporarily suspended.

3. Concurrent memory retrievals have the most detrimental effect on maintenance

• Two memory retrievals can not be performed simultaneously (Pashler, 1998; Rohrer, Pashler, Etchegarray, 1998).

• The refreshment of the decaying memory traces in STM necessitates their memory retrieval, but

Any processing component that requires retrievals from memory should have a highly detrimental effect on

concurrent maintenance of information.

4. Sharing attention is time-based

• There is a bottleneck for retrievals: only one retrieval at a time.

• Maintenance necessitates frequent retrievals

• When processing occupies the bottleneck …

Big problem

Time-Based Resource-Sharing Model

Processing Storage

Rapid switching

Switching mechanism and decay

R R R RRabbit Diner

CL

R R R RRabbit Diner

CL

R R R RRabbit Diner

CL

Possible reactivation of memory traces

Cognitive Load is

CL =Duration of attentional capture

Total time allowed

The proportion of time during which a given activity captures attention in such a way that the refreshment of memory traces is impeded.

The higher the cognitive load, the more difficult the switching.

A metric for Cognitive Load In tasks involving retrievals from LTM

The number of retrievals nTheir difficulty a

(the time they occupy central processes)

The total time allowed to perform them TWhen all the retrievals are identical in

nature:

CL = ai ni

TCL =

a N

T

R 8 3 1 6 4 K7 2 5 4 9 L63

842

Exploring cognitive load as theNumber of Retrievals / Time ratio

The Reading Digit Span Task

Read aloud the successive screens and recall the letters

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

6 Digits 10 Digits

Manipulating theNumber of Retrievals / Time ratio

Either 6 or 10 digits to be read

Constant duration of the interletter intervals (6 s)

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

Slow1000 ms

Fast600 ms


Fixed number of digits to be read

Either 600 or 1000 ms per digit

•Either 4, 8, or 12 digits during 6, 8, or 10 seconds

• 9 different values of the critical ratio (from 0.4 to 2)


Varying the number of digits to be read

and the time allowed to read them

1

1,5

2

2,5

3

3,5

4

4,5

5

5,5

6

0 0,5 1 1,5 2 2,5

Number of retrievals / Time ratio

R2 = .932


Barrouillet, Bernardin, & Camos, JEP:G, 2004

A physical law for mental effort

Cognitive Load is

CL =Work

Time

The physical law of power !

Cognitive Load of a given activity = Mental Power needed to perform it

Cognitive Loadas defined by the Time-Based Resource-Sharing model

depends on

rate of processing rather than complexity

nature of the processes involved

attentional demand of the processes

duration of the atomic steps of processing

Rate of processing rather than complexityLépine, Bernardin, & Barrouillet, EJCP, in press

In undergraduate students who remembered series of letters:

• Traditional Reading Span (self paced)

• Reading Letter Span (slow: 1200 ms per letter)

• Reading Letter Span (fast: 600 ms per letter)

1

1,5

2

2,5

3

3,5

4

4,5

RS self-paced RLS slow RLS fast

Reading letters can have the same detrimental effect on spans as reading complex sentences !

Rate of processing rather than complexityLépine, Bernardin, & Barrouillet, EJCP, in press

G 8

5

6

1 2

3P

Parity“ Even, odd, even, odd …”

location“ Up, up, down, down”

Retrievals from LTM required

Two different groups are presented with the same display but perform different activities:

Nature of the processes involvedBernardin, Portrat, & Barrouillet, submitted

G 8

5

61 2

3 P

G8

5

61

2

3 P

Regular presentation

Chaotic prese n tation

Involvement of central processes or tracking the target ?


0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

Position Parity

RegularChaotic

*ns

Tracking external events is far less demanding than occupation of central processesCognitive load mainly results from central processes occupation


R 5 3 1 2 4 K3 2 5 4 L 463

512

R 1 2 3 4 5 K1 2 3 4 L 132

465

Attentional demand of the processesGavens & Barrouillet, JML, in press

Random

Ordered

0

1

2

3

8-year olds 10-year olds

OrderedRandom

Attentional demand of the processesGavens & Barrouillet, JML, in press

Duration of the processes

CL =a N

T

Slower retrievals

Central processes occupied for a longer period

Higher CL

LOWER SPANS

A reading digit span with digits presented …

4 Four IV

442 ms 446 ms 625 ms

Reading digit spans should be lower when digits are presented in roman

Reading numbers (1 to 9) while maintaining letters1 digit per second


2

2,5

3

3,5

4

4,5

4 Four IV

Slower retrievals occupy central processes for longer periods and involve higher cognitive load.

*


Are time-constrained tasks as predictive as classical WM span tasks?

Lépine, Barrouillet, & Camos, Psych.B&R, in press

.36

.42

Compound score

Compound score.34

.50

Operation spanReading span

Classical tasks

Continuous Operation spanReading Letter span

New tasks

Standard National evaluation in litteracy

and mathematics

.39

.54

Predicting academic achievement in 93 sixth graders

Academic achievementWorking memory

The Time-Based Resource-Sharing modeland the new WM span tasks

Controling time parameters provides us with better WM span

tasks

More predictive

Simpler

Easier to manipulate

Easier to control

More knowledge free

Conclusions

The main function of WM is to share cognitive resources between maintenance and treatment: Perfect trade-off.

The more constrained this sharing, the higher the cognitive load: What matters is PACE !

Is there an intrinsic cognitive load for a given task ?: No, just an amount of work to be doneAny task that involves central processes can become very demanding when performed under sufficient time pressure.

Demanding activities in traditional cognitive psychology ?: Activities for which time pressure is inherent to their structure.

Cognitive Load is not a myth or even a metaphor. Cognitive Load is:

Proportion of time attention is totally capturedWork to be done / Time to do it

Mental power needed

Thanks to

Sophie BernardinRaphaëlle LépineNathalie GavensSophie Portrat

LEAD - CNRS Université de Bourgogne

4 icwm 2004

Technology

concurrent memory retrievals

frequent retrievals

retrievals frommemory

refreshment of memory

decaying memory traces

memory work

focus of attention

number of retrievals