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4 icwm 2004
- 1. The time-based resource-sharing model of working memory Pierre Barrouillet Valérie Camos Université de Bourgogne LEAD - CNRS
- 2. 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 ?
- 3. Time-Based Resource-Sharing Model The 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
- 4. 1. Processing and storage require attention Anderson’s ACT-R Framework Processing Maintenance Productions rules read and update the content of WM STM = Activated part of LTM Retrievals of declarative Frequent refreshment of knowledge stored in long-term decaying traces of the to-be- memory maintained items Activation is of memory items Activation attention demanding
- 5. 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.
- 6. 3. Concurrent memory retrievals have the most detrimental effect on maintenance • The refreshment of the decaying memory traces in STM necessitates their memory retrieval, but • Two memory retrievals can not be performed simultaneously (Pashler, 1998; Rohrer, Pashler, Etchegarray, 1998). Any processing component that requires retrievals from memory should have a highly detrimental effect on concurrent maintenance of information.
- 7. 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
- 8. Time-Based Resource-Sharing Model Rapid switching Processing Storage
- 9. Switching mechanism and decay Possible reactivation of memory traces CL Rabbit R R R R Diner CL Rabbit R R R R Diner CL Rabbit R R R R Diner
- 10. Cognitive Load is The proportion of time during which a given activity captures attention in such a way that the refreshment of memory traces is impeded. Duration of attentional capture CL = Total time allowed The higher the cognitive load, the more difficult the switching.
- 11. A metric for Cognitive Load In tasks involving retrievals from LTM The number of retrievals n Their difficulty a (the time they occupy central processes) The total time allowed to perform them T When all the retrievals are identical in nature: Σ ai ni aN CL = CL = T T
- 12. Exploring cognitive load as the Number of Retrievals / Time ratio The Reading Digit Span Task R8 31 Read aloud the successive screens 64 and recall the letters K7 25 49 L3 68 24
- 13. Manipulating the Number of Retrievals / Time ratio Either 6 or 10 digits to be read Constant duration of the interletter intervals (6 s) 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 6 Digits 10 Digits
- 14. Manipulating the Number of Retrievals / Time ratio Fixed number of digits to be read Either 600 or 1000 ms per digit 5 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 Slow Fast 1000 ms 600 ms
- 15. Manipulating the Number of Retrievals / Time ratio Varying the number of digits to be read and the time allowed to read them •Either 4, 8, or 12 digits during 6, 8, or 10 seconds • 9 different values of the critical ratio (from 0.4 to 2)
- 16. Manipulating the Number of Retrievals / Time ratio 6 5,5 5 4,5 4 3,5 3 2,5 R2 = .932 2 1,5 1 0 0,5 1 1,5 2 2,5 Number of retrievals / Time ratio Barrouillet, Bernardin, & Camos, JEP:G, 2004
- 17. A physical law for mental effort Cognitive Load is Work CL = Time The physical law of power ! Cognitive Load of a given activity = Mental Power needed to perform it
- 18. Cognitive Load as 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
- 19. Rate of processing rather than complexity Lépine, 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)
- 20. Rate of processing rather than complexity Lépine, Bernardin, & Barrouillet, EJCP, in press 4,5 4 3,5 3 2,5 2 1,5 1 RS self-paced RLS slow RLS fast Reading letters can have the same detrimental effect on spans as reading complex sentences !
- 21. Nature of the processes involved Bernardin, Portrat, & Barrouillet, submitted Two different groups are presented with the same display G 8 but perform different activities: 5 6 location Parity 1 2 “ Up, up, down, down” “ Even, odd, even, odd …” Retrievals from LTM required 3 P
- 22. Nature of the processes involved Bernardin, Portrat, & Barrouillet, submitted Involvement of central processes or tracking the target ? G8 G8 Chao cti ai prese n t t on 5 5 6 6 1 2 1 Regular presentation 2 3 P 3 P
- 23. Nature of the processes involved Bernardin, Portrat, & Barrouillet, submitted 4,5 ns 4 3,5 * 3 2,5 Regular 2 Chaotic 1,5 1 0,5 0 Position Parity Tracking external events is far less demanding than occupation of central processes Cognitive load mainly results from central processes occupation
- 24. Attentional demand of the processes Gavens & Barrouillet, JML, in press R5 R1 Ordered 31 23 24 45 K3 K1 25 23 Random 4L 4L 43 12 65 34 21 56
- 25. Attentional demand of the processes Gavens & Barrouillet, JML, in press 3 2 Ordered Random 1 0 8-year olds 10-year olds
- 26. Duration of the processes aN Slower retrievals CL = T Central processes occupied for a longer period Higher CL LOWER SPANS
- 27. Duration of the processes 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 letters 1 digit per second
- 28. Duration of the processes 4,5 4 3,5 * 3 2,5 2 4 Four IV Slower retrievals occupy central processes for longer periods and involve higher cognitive load.
- 29. Are time-constrained tasks as predictive as classical WM span tasks? Lépine, Barrouillet, & Camos, Psych.B&R, in press Predicting academic achievement in 93 sixth graders Working memory Academic achievement Classical tasks Operation span .36 Reading span .34 Compound score .39 Standard National evaluation in litteracy New tasks and mathematics Continuous Operation span .42 Reading Letter span .50 Compound score .54
- 30. The Time-Based Resource-Sharing model and the new WM span tasks More predictive Controling time Simpler parameters provides us with better WM span Easier to manipulate tasks Easier to control More knowledge free
- 31. 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 done Any 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 captured Work to be done / Time to do it Mental power needed
- 32. Thanks to Sophie Bernardin Raphaëlle Lépine Nathalie Gavens Sophie Portrat LEAD - CNRS Université de Bourgogne
Notes de l'éditeur
- However, little is known about the precise mechanisms that underlie WM functioning, and many questions remain unanswered.
- Our model is aimed to answer these questions. It is based on four main proposals
- As far as the first proposal is concerned, we assume that processing and storage both require attention. Within the ACT-R framework, processing most often require to retrieve knowledge from long-term memory, e.g., for reading, or solving operations. The storage component requires to regularly retrieve the items of relevant information because their memory traces suffer from a decay and tend to fade away. Thus, both activities require retrievals from memory that require attentional focusing and thus attention
- Second, we assume that the activation of memory items is produced by attentional focusing, as suggested by many models of WM such as Anderson ’ s ACT-R or Cowan ’ s model. Thus, when the focus of attention is switched away, activation declines with time.
- Third, According to Pashler, there is a central bottleneck that constrains retrievals. Thus, it would be impossible to perform simultaneously two memory retrievals. The retrievals required by processing impede the refreshment of ST memory traces. As a consequence …
- Forth, sharing attention is time-based. because there is a central bottleneck, the memory retrievals needed by the processing component captures attention and, as a consequence, the memory traces decay and vanish. We have a problem
- Thus, The solution is to rapidly switch between processing and storage.
- We assume that the constraints on the switching process determines cognitive load. Suppose that your are performing a WM span task, and that you are successively presented with these two words. Unfortunately, you have to perform some intervening task during the interval. This task involves memory retrievals, during which the memory traces of the words decay, but you can keep free short slots to retrieve and refresh these traces. Let us suppose that this activity involves a moderate cognitive load. Now, if you are given more time to perform the same task, you have longer periods of time to reactivate memory traces. The WM task becomes easier/ because cognitive load decreases On the other hand, if the time is reduced, it becomes difficult to concurrently refresh memory traces. Cognitive load increases /and WM span should decrease.
- CL depends on the number and difficulty of retrievals because retrievals, among other processes, block attention for a portion of time
- According to this analysis, the CL of a task that mainly involves memory retrievals depends on three parameters: the number of retrievals it requires, their difficulty, (some retrievals need more time than others), and the time allowed to perform them CL is given by the following equation, Which can be simplified when all the retrievals are identical in nature and difficulty. CL depends on the Number of retrievals / Time ratio .
- Our second hypothesis concerned the effect of time on cognitive load. Thus we tested our hypothesis that CL is a function of the number of retrievals / Time ratio We used a very simple task, the reading digit span task letters to be remembered and digits to be read are successively presented on screen And subjects are asked to read them aloud and to recall the letters.
- As we predicted, increasing the number of digits to be read had a detrimental effect on span
- Once more, there was a clear effect of pace. The faster the pace, the lower the span. Note that in this case, the task remained unchanged and its duration was reduced. Thus, the delays of retention were reduced. Towse and Hitch would predict higher spans for shorter delays. But shorter delays resulted in lower spans, that is absolutely at odds with their hypothesis.
- We verified the predictive value of the equation in a study in which we varied both the number of digits to be read and the time allowed to read them.
- As we predicted, WM spans decreased as CL of the reading digits tasks increased. As expected, the same phenomenon was observed in the baba span, but of course less pronounced
- What is CL? CL is in fact a function of the cognitive work to be done, divided by the time to do it. This function corresponds to the physical law of power. Cognitive load corresponds to the mental power needed to perform an activity. This means that simple tasks can result in very high cognitive load.
- Recall that our theory predicts that very simple tasks can have a highly detrimental effect on spans because complexity does not matter. What is important is pace. Actually, our experiments support this prediction. We can compare three tasks in which undergraduate students had to recall letters: The operation span that involves a quite complex activity of problem solving The continuous operation span in which adults have just to solve very elementary operations like adding or subtracting 1 or 2 And the reading digit span in which adults have just to read digits, a very simple activity.
- The mean reading digit span was about 3 Not surprisingly, continuous operation span is slightly lower than the reading digit span, But operation span is better! Lire l ’ écran
- We predicted also that among attention-demanding activities, the retrievals should have the most detrimental effect because retrievals are also needed to refresh decaying memory traces in STM. We designed a task … Our prediction is that, all other thinks being equal, the parity task would result in lower spans than the decision about location.
- In the same experiment, we compared spans from parity and location tasks in which the targets were not presented at a regular and smooth rhythm but at a Chaotic rhythm
- As we expected, an activity that requires retrievals from LTM is more disruptive than an activity that just requires response selection. By contrast, the way the targets are presented had only a small and non significant effect.
- If our analysis is correct, the time a given activity blocks the central processes has a direct impact on the CL. This is the parameter a in the CL equation. For example, slower retrievals occupy the central processes for longer periods of time, Thus involve a higher CL and then lower spans.
- We compared three conditions of a reading digit span in which numbers were presented either in their Arabic Verbal or Roman form. The corresponding Reading times are … Thus we predicted lower spans when numbers are presented in their Roman form.
- As predicted by the reading times, there was no big difference between spans when digits were presented in Arabic or Verbal form. However, the roman presentation, which takes longer to read resulted in lower spans. As preicted by the Time-based resource sharing model …
- The main interest of WM span tasks is their predictive value. Are the new tasks as predictive as the classical operation or reading span tasks? We investigated this question by evaluating the correlation between WM spans and academic achievement in 93 sixth graders. We used classical … as well as new WM span tasks. The reading letter span task is a task ni which children had to read letters on successive screens while remembering digits. Academic achievement was evaluated using the score on the national tests. The venerable operation span made a good job with a correlation of .36 But continuous operation span was slightly better. Daneman and Carpenter ’ s reading span was not so bad, but the reading letter span was far more predictive. In fact, when we compared the compound scores, the classical tasks correlated with academic achievement, but the new tasks were more predictive.
- In fact, time-constrained tasks have many advantadges. They are more predictive, but also they are simpler They are easier to manipulate. For example, we can easily manipulate the duration of the task, its difficulty They are easier to control, because they are computer-paced and you can control subject ’ s activity And finally, they are more knowledge free. They involve simple activities that everybody is able to complete. Some sixth graders are probably poor readers, or mathematically disabled, but they are all able to read letters or digits. Thus low spans can not be due to the fact that the subject is unable to correctly perform the secondary task.
- Some provisional conclusions from a work in progess.