5 psychonomic 2005 1

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  • WM is a system devoted to the maintenance of relevant information during processing Thus WM span tasks usually involve these two activities  with some memory items to be maintained  while a concurrent processing must be performed
  • For example, in the well known Operation span, participants are asked to solve arithmetic equations while maintaining words to be recalled at the end of the series.
  • We recently proposed a model accounting for the cognitive processes involved in WM span tasks, the TBRS model. In its initial version, the TBRS model was based on five main proposals 
  • Within this model, the main point is probably that resource sharing is achieved through a rapid switching between processing and maintenance that occurs during the processing component of the task.
  • 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 for example successive 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.
  • In this account, CL depends on the number and difficulty of retrievals because retrievals block attention for a portion of time.  In other words CL is given by this equation  the proportion of time during which attention is captured. 
  • According to this analysis, the CL of the task we presented above 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, CL depends here on the Number of retrievals / Time ratio .
  • CL, and as a consequence WM spans, would thus depend on three main parameters  Rate of processing rather than complexity of the processing component  (lire) with long durations resulting in higher CL and lower spans  (lire) Because we initially assumed that retrievals are more damaging than other activities
  • Let us recall what happens when the rate of processing is manipulated
  • We tested the hypothesis that CL is a matter of rate of processing  using 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.
  • First we manipulated the number of retrievals while keeping time constant  so, we presented either 6 or 10 digits  Within constant interletter intervals of 6 s  As we predicted, increasing the number of digits to be read had a detrimental effect on span
  • Then we manipulated the time allowed to perform an unchanged task  We presented a constant number of digits  That were presented either 600 or thousand ms  Once more, there was a clear effect of pace. The faster the pace, the lower the span.
  •  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.  (lire)  (lire)
  •  As we predicted, WM spans smoothly decreased as the CL of the reading digit task increased.  and the regression line  Nicely fitted these points
  • 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 compared three tasks in which undergraduate students had to recall digits:  in the traditional RS, adults were asked to read and understand sentences  Whereas in the reading letter span task, they were just asked to read successive letters presented at a slow  Or fast pace And the reading digit span in which adults have just to read digits, a very simple activity.
  •  The mean reading span was about 3  Not surprisingly, the reading letter span was higher and above 4  But when performed at a fast pace, the task became as difficult as the reading span task  (lire)
  • Now the second point concerning the duration of processing steps
  • If our analysis is correct, the time a given activity blocks the central processes has a direct impact on the CL. 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 task in which numbers were presented either in their  Arabic  Verbal or  Roman form. The corresponding Reading times are …    wit the roman form that takes longer   Thus we predicted lower spans when numbers are presented in their Roman form.  Participants had to read numbers while maintaining letters  At a rate of 1 digit per s.
  • As predicted by the reading times  there was no big difference between spans when digits were presented in Arabic  or Verbal form.  but, the roman presentation, which takes longer to read resulted in lower spans.   As predicted by the Time-based resource sharing model …  (lire)
  • Our last point concerns the impact of nature of the processes
  • Remember that we predicted 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 …  in which participants had to maintain letters and process numbers but  in two different ways  One group had to judge the parity of the number  Whereas the other was just asked to judge their location on screen  Our prediction was, all other thinks being equal, that the parity task would result in lower spans than the location task.
  •  As we expected, an activity that requires retrievals from LTM is more disruptive than an activity that just requires response selection.  Retrievals seem to be more demanding
  • But, what is the locus of the effect, the nature of the task or its duration
  • What is needed is a careful control of the actual processing time  For example, using the same task  We could measure the time taken to evaluate the parity of each number  Or its location  The actual processing time is the sum of these RTs
  • Thus we designed an experiment in which adults were asked to  Maintain series of letters  With interletter intervals of 6400 ms  During which were presented either 4, 6, or 8 numbers for a parity or a location task  The responses were given by pressing keys  And we used 6 independent groups
  • As we already knew, the spans decreased when the number of stimuli increased
  • And the parity task resulted in lower spans
  • Concerning the actual duration of processing, of course it increased with the number of stimuli to process
  • Concerning the actual duration of processing, of course it increased with the number of stimuli to process
  • To answer the question, we have to analyse spans as a function of time.  These are the actual processing times for the location span task  And the resulting spans observed Would these spans differ from the parity spans if the two tasks involved the same durations?  Remember that the parity judgments took longer
  • To answer the question, we have to analyse spans as a function of time.  These are the actual processing times for the location span task  And the resulting spans observed Would these spans differ from the parity spans if the two tasks involved the same durations?  Remember that the parity judgments took longer
  • To answer the question, we have to analyse spans as a function of time.  These are the actual processing times for the location span task  And the resulting spans observed Would these spans differ from the parity spans if the two tasks involved the same durations?  Remember that the parity judgments took longer
  • To answer the question, we have to analyse spans as a function of time.  These are the actual processing times for the location span task  And the resulting spans observed Would these spans differ from the parity spans if the two tasks involved the same durations?  Remember that the parity judgments took longer
  • To answer the question, we have to analyse spans as a function of time.  These are the actual processing times for the location span task  And the resulting spans observed Would these spans differ from the parity spans if the two tasks involved the same durations?  Remember that the parity judgments took longer
  • Thus there is no difference between tasks when durations were equated.  Our question was  And the answer is
  • 5 psychonomic 2005 1

    1. 1. Do Working Memory Spans Depend only on Time? Valérie Camos Pierre Barrouillet Université de Bourgogne LEAD - CNRS
    2. 2. Working Memory Span TasksThey involve:• Maintenance: items to be maintained and recalled• Processing: some task, usually complex, such as readingcomprehension or problem solving
    3. 3. Working Memory Span Tasks(6/3)+5=7? Operation span (Turner & Engle, 1989) Truck (3+6)/3=2? Deer (8-6)x3=6? Nail Recall
    4. 4. Time-Based Resource-Sharing Model The main proposals Barrouillet, Bernardin, & Camos, JEP:G, 20041. Processing and maintenance require attention which is a limited resource (somesharing is needed)2. As soon as attention is switched away from the memory items, their activationsuffers from a time-related decay3. Refreshing the decaying memory traces necessitates their retrieval throughattentional focusing (as proposed by Cowan, 1999)4. When processing component requires retrievals from LTM, it should have themost detrimental effect on concurrent maintenance5. In this case, sharing attention is time based because a central bottleneck allowsonly one retrieval at a time
    5. 5. Time-Based Resource-Sharing Model Rapid switchingProcessing Maintenance
    6. 6. Switching mechanism and decay Possible reactivation of memory traces CLTruck R R R R Deer CLTruck R R R R Deer CLTruck R R R R Deer
    7. 7. Cognitive Load is Duration of attentional capture CL = Total time allowedThe proportion of time during which a given activity captures attention in such a way that the refreshment of memory traces is impeded.
    8. 8. A metric for Cognitive Load In tasks involving retrievals from LTMThe number of retrievals nTheir difficulty a (the time they occupy central processes)The total time allowed to perform them T aN CL = T
    9. 9. Cognitive Loadas defined by the Time-Based Resource-Sharing model depends on  rate of processing rather than complexity  duration of the atomic steps of processing  nature of the processes involved
    10. 10. Cognitive Loadas defined by the Time-Based Resource-Sharing model depends on  rate of processing rather than complexity  duration of the atomic steps of processing  nature of the processes involved
    11. 11. Rate of Processing Manipulating the Number of Retrievals / Time ratio The Reading Digit Span TaskR8 31 Read aloud the successive screens 64 and recall the letters K7 25 49 L3 68 24
    12. 12. Rate of Processing Manipulating the Number of Retrievals / Time ratioEither 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
    13. 13. Rate of ProcessingManipulating the Number of Retrievals / Time ratioFixed 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
    14. 14. Rate of ProcessingManipulating 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)
    15. 15. Rate of Processing 6 5,5 5 4,5 4Mean Span 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
    16. 16. Rate of processing rather than complexity Lépine, Bernardin, & Barrouillet, EJCP, 2005In undergraduate students who remembered series of digits: • Traditional Reading Span (self paced) • Reading Letter Span (slow: 1200 ms per letter) • Reading Letter Span (fast: 600 ms per letter)
    17. 17. Rate of processing rather than complexity Lépine, Bernardin, & Barrouillet, EJCP, 2005 4,5 4 3,5 WM span 3 2,5 2 1,5 1 RS self-paced RLS slow RLS fastReading letters can have the same detrimental effect on spans as reading complex sentences !
    18. 18. Cognitive Loadas defined by the Time-Based Resource-Sharing model depends on  rate of processing rather than complexity  duration of the atomic steps of processing  nature of the processes involved
    19. 19. Duration of the atomic steps of processing Slower retrievals Central processes occupied for a longer period Higher CL LOWER SPANS
    20. 20. Duration of the atomic steps of processing A reading digit span with digits presented … 4 Four IV 442 ms 446 ms 625 msReading digit spans should be lower when digits are presented in romanReading numbers (1 to 9) while maintaining letters1 digit per second
    21. 21. Duration of the atomic steps of processing 4,5 4 * WM span 3,5 3 2,5 2 4 Four IV Slower retrievals occupy central processes for longer periods and involve higher cognitive load.
    22. 22. Cognitive Loadas defined by the Time-Based Resource-Sharing model depends on  rate of processing rather than complexity  duration of the atomic steps of processing  nature of the processes involved
    23. 23. Nature of the processes involved Bernardin, Portrat, & Barrouillet, in press 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 Lower spans predicted P
    24. 24. Nature of the processes involved Bernardin, Portrat, & Barrouillet, in press 4,5 4 3,5 * 3 WM span 2,5 2 1,5 1 0,5 0 Location ParityRetrievals from LTM more demanding than location judgments
    25. 25. Nature of the processes or time ??? Parity judgments involve lower spans but …they probably take also longer !
    26. 26. Nature or duration of the processes involved?WM spans as a function of the actual processing time within the interletter interval 4 7 2 T 9 K Stimulus onset ResponseParity RT Actual Processing Time = Σ RTLocation
    27. 27. Nature or duration of the processes involved? Series of ascending length of 1 to 7 letters to be remembered (3 series ofeach length) Interletter intervals 6400 ms Either 4, 6, or 8 stimuli to be processed in each interval Responses by pressing keys 2 Tasks x 3 Rates = 6 groups of 16 adults
    28. 28. Spans as a function of the number of stimuli and the nature of the task 6 Location 5.5 5 4.5 Mean span 4 3.5 3 2.5 2 4 6 8 Number of stimuli
    29. 29. Spans as a function of the number of stimuli and the nature of the task 6 Location 5.5 Parity 5 4.5 Mean span 4 3.5 3 2.5 2 4 6 8 Number of stimuli
    30. 30. Actual duration of processing as a function of the task and number of stimuli 4 3.5 3 Actual duration of processing Location 2.5 2 1.5 1 0.5 0 4 6 8 Number of stimuli
    31. 31. Actual duration of processing as a function of the task and number of stimuli 4 Parity 3.5 3 Actual duration of processing Location 2.5 2 1.5 1 0.5 0 4 6 8 Number of stimuli
    32. 32. Nature or duration of the processes involved? 6.5 6 Observed location spans 5.5 Mean Span 5 4.5 4 3.5 3 1.5 2 2.5 3 3.5 4 Actual Interletter Processing Time (sec)
    33. 33. Nature or duration of the processes involved? 6.5 6 5.5 Mean Span 5 4.5 4 3.5 3 1.5 2 2.5 3 3.5 4 Actual Interletter Processing Time (sec)
    34. 34. Nature or duration of the processes involved? 6.5 6 Predicted span values for a 5.5 location task thatobserved Parity spans would take longer Mean Span 5 4.5 4 3.5 3 1.5 2 2.5 3 3.5 4 Actual Interletter Processing Time (sec)
    35. 35. Nature or duration of the processes involved? 6.5 6 Mean location span 5.23 5.5 Mean parity span observed Mean Span 5 4.48 4.5 Mean span predicted 4.34 4 3.5 3 1.5 2 2.5 3 3.5 4 Actual Interletter Processing Time (sec)
    36. 36. Nature or duration of the processes involved? 6.5 6 Mean location span 5.23 5.5 Mean parity span observed Mean Span 5 4.48 4.5 Mean span predicted 4.34 4 3.5 3 1.5 2 2.5 3 3.5 4 Actual Interletter Processing Time (sec)
    37. 37. Tasks have no effect on spans beyond their durationDo working memory spans depend only on time?Working memory spans depend on the time during which the processing component captures attention
    38. 38. Thanks to Sophie Bernardin Raphaëlle Lépine Nathalie Gavens Sophie Portrat LEAD - CNRS Université de Bourgogne

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