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Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uear20
Subjective ordering, working memory, and aging a
Sjoerd Wiegersma & Karin Meertse
a
a
University of Utrecht Published online: 27 Sep 2007.
To cite this article: Sjoerd Wiegersma & Karin Meertse (1990) Subjective ordering, working memory, and aging, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 16:2, 73-77, DOI: 10.1080/07340669008251530 To link to this article: http://dx.doi.org/10.1080/07340669008251530
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
73
Experimental Aging Research, Volume 16, Number 2, 1990, ISSN 0734-0664 O1990 Beech Hill Enterprises Inc.
Subjective Ordering, Working Memory, and Aging SJOERDWIEGERSMA AND KARINMEERTSE
Downloaded by [Central Michigan University] at 15:00 31 December 2014
University of Utrecht
Cognitive decline in aging was studied by presenting four tasks involving short-term memory to young and old adults: digit span forward, missing scan, randomization span, and randomization span visual. Results showed that performance declined significantly with age in the latter two tasks, which require subjective ordering of a sequence of responses, and not in the first two tasks, which involve reproduction of a presented sequence and searching and comparison processes.
I
n reviews on age differences in adult human memory, Craik (1977) and Craik and Rabinowitz (1984) proposed that, whereas primary memory seems to remain intact with aging, there is a decline in the division of attention and the reorganization of material. A number of studies have documented the decline of performance with age in tasks requiring the division of attention among stimuli (Broadbent & Gregory, 1965; Parkinson, Lindholm, & Urell, 1980) or among competing operations (Broadbent & Heron, 1962; Gick, Craik, & Morris, 1988; Morris, Gick, & Craik, 1988; Wingfield, Stine, Lahar, & Aberdeen, 1988; Wright, 1981). The second aspect of the cognitive decline with age, reorganization of material, has been studied less widely. Reorganization of material taxes attentional capacity as opposed to passive repetition of material which poses minimal demands on attention. Hence, aging should affect the active processing aspects of working memory rather than the passive holding aspects (Gick et al., 1988; Morris et al., 1988). In the present study, four tasks involving short-term retention are presented to young and old adults. The four tasks all require the manipulation of numbers, but differ with respect to the degree and type of controlled processing and reorganization of material. The first task is digit span forward. Subjects are presented with random sequences of numbers of increasing lengths which have to be repeated immediately after presentation. This is assumed to have minimal requirements for reorganization of material, since subjects tend to repeat the sequence in the presented order. This is in line with findings that the digit spans of the aged are within the normal range of young adults, although at the lower end of the distribution (Parkinson, 1982). Digit span is mainly determined by passive recency effects and
the articulatory loop, which do not tax working memory capacity (Spinnler, Della Sala, Bandera, & Baddeley, 1988). In the present study, this task is mainly presented for the purpose of getting a baseline measure for comparison with the other three tasks requiring different types of processing. The second task is the missing scan. Random permutations of increasing sets of numbers (1-3, 1-4, etc.) are presented, in each of which one number is missing. It is the task of the subject to detect the missing item. In this task, the subject compares two sets of items: the set of designated numbers activated by instruction and those serially presented, searching the items of the first list while testing whether they are in the second (Buschke & Lenon, 1969; Yntema & Trask, 1963). This task requires the short-term retention of all numbers until the last item has been presented, as was the case in digit span forward. The task has low demands on active production processes and reorganization of material. Eventual differences on this task between young and old adults should be explained by the complexity of the comparison processes (searching and testing) involved. These processes are primarily based on recognition and, therefore, have low demands on retrieval and production, since only one single response is required (Buschke, 1963; Madsen & Drucker, 1966). The third task, randomization of a sequence of numbers, requires the production of all numbers of a set (1-3, 1-4, etc.) in a self-chosen ordering, with the explicit instruction not to produce any of these numbers twice or to use counting orders. This task requires the short-term retention of all produced numbers until the last number has been produced. It has been found in randomization, even when repetitions are not prohibited by instruction,
Correspondence and reprint requests should be addressed to Dr. S. Wiegersma, University of Utrecht, Vakgroep Psychonomie, Heidelberglaan 2, 3584 CS Utrecht, THE NETHERLANDS.
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that subjects tend to avoid repetition over distances of six or more items back in memory. A comparison mechanism, assuming short-term retention, can explain how such avoidance of repetition comes about (Wiegersma, 1982a, 1982b, 1984). One difference with the missing scan is clear: the order of the items in the missing scan is determined by the experimenter, whereas the randomization task requires ordering by the subject. This can be considered an instance of reorganization of material: the serially-ordered set of numbers must be subjectively reordered. The comparison processes in the randomization and missing-scan tasks are assumed to be approximately equal. However, some differences must be discussed. In the missing scan, comparison between designated and presented items is assumed to occur once, after all the items have been presented. In randomization, the subject must make a comparison of sets for every response made, with an increasing set of produced responses to compare with the designated ones when the sequence is growing. However, it seems reasonable to assume that in the latter task performance is determined by the last responses of the produced sequence, where the limits of performance are approached. The responses produced earlier in a sequence are easier to find, since fewer comparisons with earlier responses are required. Moreover, they are no burden for producing later responses. On the contrary, the extra comparisons made for earlier responses might provide extra practice in the randomization task, resulting in better performance with later responses. It is not clear whether or not subjects make such early comparisons in the missing scan, where no response is required until the last item has been presented. In conclusion, the comparison processes in randomization do not seem more difficult than those involved in the missing scan task. The difference between both tasks is in the additional load on reorganization of material in the randomization task. The fourth task, randomization-visual, is identical to the third, except that with each vocal response production all choice alternatives are presented to the subject in a different visual arrangement. Such a task was originally used by Petrides and Milner (1982) in a study of the cognitive disorders of frontal-lobe patients. Our task differs from theirs in that the choice alternatives are numbers and in the use of vocal responses rather than pointing responses. The subject has to select one number response from each sheet of paper, while the experimenter turns them over, and has to avoid repetition and counting orders. The difference with randomization is small. In randomization, the responses have to be selected from a memory set of responses which remains continuously activated during production of the sequence. In randomization-visual, such a memory representation does not seem to be required, since the choice alternatives are presented at each trial. However, since the alternatives are presented in a new arrangement at each trial, subjects seem to use a memory set of choice alternatives, just as they do in randomization, rather than relying on the vicissitudes of the visual display.
In summary, the digit span is assumed to measure storage capacity with low demands on processing capacity, the missing scan measures comparison processes in addition to storage capacity and the randomization tasks measure reorganization of material in addition to the processes involved in the other tasks. If there is a decline with age in the search for and comparison of information, differences between old and young adults should show up in missing scan as well as randomization. If the decline is due to reorganization of material, only the two randomization tasks should be affected by age.
Method
Design Four experimental tasks were presented to groups of young and old adults: digit span forward, missing scan and two subjective ordering tasks: randomization span and randomization span visual. The tasks were presented to 12 young adults and 12 older adults, in an order determined by latin squares providing balanced counterbalancing (Edwards, 1968, pp. 191-193). After these tasks had been completed, two additional tasks, digit span backward and word fluency were presented. Both of these tasks require sequential reorganization by the subject. Digit span backward was considered interesting because of previous findings of aging effects in this task, as contrasted with digit span forward (Bromley, 1958). Word fluency was tested with semantic categories (animals and professions) and initial letters (S, M and K).Subjects had to produce as many words of each type as they could within one minute. Aging effects on word fluency tasks have generally been found (e.g. , Howard, 1980; Schonfield & Stones, 1979).
Subjects Twelve young adults (mean age: 23.8 yrs; range: 16-33 yrs) and 12 aged adults (mean age: 70.7 yrs; range: 63-79 yrs) participated. There were six men and six women in the group of young adults and seven men and five women in the group of aged adults. The groups differed in the degree of educational level: mean years of education were 12.6 in the young and 8.6 in the aged group. In evaluating differences between age groups, this confounding of age and educational level was accounted for by treating the latter variable as a covariate in the analysis.
Procedures All four experimental tasks rely heavily on short-term memory and involve the use of numbers. The tasks differ in the extent to which they require control processes and attention. Digit span forward. A subset of the numbers 1- 12 was presented aurally at a rate of one number per second, for immediate recall by the subject. The first sequence consisted of three numbers, followed by four, five, etc. One
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SUBJECTIVE ORDERING
additional three-number trial served as practice for the subject. For comparability with the other tasks free recall, rather than the usual ordered recall was allowed (Buschke, 1963). When no errors were made, there was one trial at each level. In the case of an error, the subject did an additional trial at the same level. The subject earned three points if the first level of three numbers was successfully completed and one additional point for each first trial of a higher level performed correctly, and 0.5 point for the correct performance of a second trial. If both trials at one level were wrong, testing was stopped. Missing scan. Random sequences of n-1 numbers, randomly selected from sets of n numbers, were presented to the subject at the rate of one per second. Set size (n) was gradually increased from 3 (numbers I-3), through 4 (1-4), etc., until the subject failed to mention the missing number. There was one trial at each level as long as the subject was correct. In the case of failure, an additional trial at the same level was performed. Scoring was as for digit span. Randomization. Subjects had to select responses from increasing sets of numbers (1-3, 1-4, etc.) in a self-chosen ordering, until they produced a sequence in which one or more repetitions occurred. In addition to that, subjects were required to avoid counting orders (e.g., ‘3,4’). If the subject used such stereotyped order despite the instruction he/she got an additional trial at the same level, after the instruction to avoid counting had been repeated. Violation of this requirement in subsequent trials was counted as an incorrect trial. At each trial a randomly chosen number was given to the subject to start with. In order to avoid too high requirement on speed, especially for the aged, subjects were allowed to produce the sequence at a self-paced rate. Randomization-visual. This task was identical to the randomization task, except that all choice alternatives were presented to the subject in a different visual arrangement with each vocal response production. A comparable task, but requiring pointing rather than verbal responses, has been used by Petrides and Milner (1982) and Wiegersma, Van der Scheer and Hijman (1990) for the study of patients with frontal-lobe lesions. The subjects selected one of n alternative numbers from sheets of paper, while the experimenter turned them over at a rate determined by the speed of production of the subject. The instructions and scoring were the same as in the randomization task. All four tasks started with one practice trial at level three. For the last three tasks, the relevant set of responses of each trial was presented aurally as well as visually on a card, which was turned over before the trial started.
Materials The numbers 1-12 were used in all four tasks, except the missing scan in which four extra levels were prepared (up to the numbers 1-18), because of the higher spans found on this task.
12
r-
10
I
I
I
I
i
-
C
a a
a-
cn 6-
1 DS
T
MS a s
R k
RV
FIGURE 1. Mean span scores of young and old adults at four tasks involving short-term memory. DS = diglt span, MS = misslng scan, R = randomization, and RV = randomization visual.
Results Experimental Tasks Mean spans of the two age groups are shown in Figure 1 . An analysis of covariance with repeated measures over tasks and level of education as a covariate (Winer, 1970, pp. 606-618) showed a significant effect of age group (F [1,21] = 14.98, p < .025), of task, (F [3,66] = 69.89, p < .025) and a significant interaction effect of group with task (F [3,66] = 3.49, p < .025). Separate analyses of covariance for each task showed significant group differences for randomization (F[1,21] = 6.83, p < .025) and randomization-visual (F[ 1,211 = 1 1.70, p < .025), but not for digit span and missing scan (I,> .05 in both cases). The proportions of variance accounted for by the experimental treatments (q*)in these analyses are 14.8% for digit span, 15.7% for missing span, 32.4% for randomization, and 55.8% for randomization-visual. That level of education was not responsible for the differences in subjective ordering between groups was further supported by the lack of correlation of this variable with randomization (r = - .02 and - .21 for the young and the aged respectively,) and randomization-visual(r = .08 and . l 1 for the young and the aged respectively).
Backward Span and Word-Fluency Tasks Backward span was lower for the older adults (M = 4.25, SD = .62) than for the younger adults (M= 4.96,
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WIEGERSMA/MEE:RTSE
SD = .62), as shown by an analysis of variance (F[ 1,221 = 7.81, p = .Ol), but the difference was almost entirely due to the difference in educational level between the groups as shown by an analysis of covariance in which the covariate educational level was significant (F [1,21] = 6.93, p = .02), leaving a nonsignificant effect due to age. Word-fluency scores were lower in the older than in the younger adults (the mean numbers of words produced were 16.8 (SD = 2.4) vs. 21.5 (SD = 3.0) for categories, and 11.0 (SO = 6.3) vs. 17.6 (SD = 4.0) for letters). The effect of age for both scores together was significant as shown by an analysis of covariance (F[1,21] = 4.60, p < .05), and so was the effect of the covariate level of education (F [1,21] = 12.37, p < .01). Correlations Bet ween Tasks Correlations between tasks were calculated in order to get an estimate of the degree to which the tasks measure shared processes (Table 1). Correlations with age partialled out are shown in parentheses in the same table. The missing scan only correlated with digit span forward and not with any of the other tasks. The subjective ordering tasks both correlated significantly with the word fluency tasks and with digit span backward. After age was partialled out, intercorrelations between tasks tend to disappear.
Discussion The results are as predicted: performance of older subjects is reduced relative to younger subjects when tasks require active production. No differences between age groups are found when tasks require minimal production (the missing scan) or simple recall of a sequence (the digit span forward). It is not the degree to which production is involved which determines the aging effect, but the extent to which production requires active ordering by the subject.
The active ordering required by these tasks consists of at least two components, a comparison process leading to the finding of nonrepetitions and the selection and monitoring of responses. The comparison process does not seem responsible for the decline with age in subjective ordering, since the missing scan shows highly intact performance. This finding is in line with the general notion that the cognitive decline with age is due to reduced attentional processing capacity, while the automatic processes would remain intact. The remaining component, response selection and monitoring, must be responsible for the aging effect in the subjective ordering tasks. This involves first, the selection of candidate responses from the nonrepetitions which are output of the comparison process, and second, monitoring of the selected response. The monitoring process is required for the suppression of counting orders. It has been found that counting orders in randomization increase with larger sets of choice alternatives and simultaneous performance of a second task, presumably due to limited processing capacity (Wiegersma, 1982a). In conclusion, our results are in line with Craik and Rabinowitz’ (1984) hypothesis that reorganization of material declines with age. However, we suggest that it is the selection and monitoring component rather than the comparison component of reorganization which declines. The absence of an aging effect on digit span forward confirms earlier findings, but there was no effect of age on digit span backward. We found a group difference in the latter task, but it was no longer significant when educational level was partialled out. Bromley ( 1 958) found a reliable difference between age groups matched for educational level, but the difference was small (0.5 as compared to 0.7 in this study) and based on a large number of subjects (200). The differences between young and old adults are substantially larger in randomization (1.9) and randomization visual (3.0). The absence of an age difference in the missing scan might seem somewhat surprising, since the main determinant of performance is supposed to be search and com-
TABLE 1 Product-Moment Correlations Between Tasks (in parentheses: correlations with age partialled out), Over All 24 Subjects
DS
MS
.42* (.36) .57* (.49*) .30 (.07) .46* (.35) .36 (.17) .40 (.25)
.25 (.15) .15 (-.04) . I 5 (.01) .10 (-.lo) .27 (.16)
R
RV
~~
MS R RV Backward Span Word Fluency - C. Word Fluency - L.
.57* (.32)
.58* (.41) .51* (.24) .50* (.28)
Note. DS = digit span forward; MS = missing scan; R = randomization; RV= randomization visual. * p < .05, two-sided test.
.54*
(.24) .47* ( - .07) .61* (.32)
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SUBJECTIVE ORDERING
parison in short-term memory. Such processes have also been studied with binary-classification RT tasks and showed effects of aging. The time for comparison was found to be longer when people get older (Anders & Fozard, 1973; Anders, Fozard, & Lilliquist, 1972; Madden & Nebes, 1980). However, although the search and comparison processes may be comparable in both tasks, an important difference might be that the RT task puts great emphasis on speed, which is not critical in the missing scan. Madden and Nebes (1980) showed that, while comparison time increases, the number of errors made by the subject does not increase with age, when both speed and accuracy are stressed equally by instruction. So, these results are not necessarily in contradiction with our results in the missing scan task, which requires accuracy rather than speed.
References Anders, T.R., & Fozard, J.L. (1973). Effects of age upon retrieval from primary and secondary memory. Developmental Psychology, 9, 41 1-415. Anders, T.R., Fozard, J.L., & Lilliquist, T.D. (1972). The effect of age upon retrieval from short-term memory. Developmental Psychology, 6, 214-217. Broadbent, D.E., & Gregory, M. (1965). Some confirmatory results on age differences in memory for simultaneous stimulation. British Journal of Psychology, 56, 77-80. Broadbent, D.E., & Heron, A. (1962). Effects of a subsidiary task on performance involving immediate memory in younger and older men. British Journal of PSyChOlOgy, 53, 189- 198. Bromley, D.B. (1958). Some effects of age on short term learning and remembering. Journal of Gerontology, 13, 398-406.
Buschke, H. (1963). Retention in immediate memory estimated without retrieval. Science, 140, 56-57. Buschke, H., & Lenon, R. (1969). Ordinal sequence in short-term retention of numbers. Journal of Experimental Psychology, 81, 201-203. Craik, F.I.M. (1977). Age differences in human memory. In J.E. Birren & K.W. Schaie (Eds.), Handbook of thepsychology of aging (pp. 384-420). New York: Van Nostrand Reinhold. Craik, F.I.M., & Rabinowitz, J.C. (1984). Age differences in the acquisition and use of verbal information. In H. Bouma & D.G. Bouwhuis (Eds.), Attention and performance X(pp. 471-499). Hillsdale, NJ: Erlbaum. Edwards, A.L. (1968). Experimental design in psychological research. New York: Holt, Rinehart, & Winston. Gick, M.L., Craik, F.I.M., & Morris, R.G. (1 988). Task complexity and age differences in working memory. Memory and Cognition, 16, 353-361.
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Howard, D.V. (1980). Category norms: A comparison of the Battig and Montague (1969) norms with the responses of adults between the ages of 20 and 80. Journal of Gerontology, 35, 225-23 1. Madden, D.J., & Nebes, R.D. (1980). Aging and the development of automaticity in visual search. Developmental Psychology, 16, 377-384. Madsen, M.C., & Drucker, J.M. (1966). Immediate memory by missing scan and modified digit span. Psychonomic Science, 6, 283-284. Morris, R.G., Gick, M.L., & Craik, F.I.M. (1988). Processing resources and age differences in working memory. Memory and Cognition, 16, 362-366. Parkinson, S.R. (1982). Performance deficits in shortterm memory tasks: A comparison of amnesic Korsakoff patients and the aged. In L.S. Cermak (Ed.), Human memory and amnesia (p. 77-96). Hillsdale, NJ: Erlbaum. Parkinson, S.R., Lindholm, J., & Urell, T. (1980). Aging, dichotic memory and digit span. Journal of Gerontology, 35, 87-95. Petrides, M., & Milner, B. (1982). Deficits on subjectordered tasks after frontal- and temporal-lobe lesions in man. Neuropsychologia, 20, 249-262. Schonfield, D., & Stones, M.J. (1979). Remembering and aging. In J.F. Kihlstrom & F.J. Evans (Eds.), Functional disorders of memory (pp. 103-139). Hillsdale, NJ: Erlbaum. Spinnler, H., Della Sala, S., Bandera, R., & Baddeley, A. (1988). Dementia, aging, and the structure of human memory. Cognitive Neuropsychology, 5, 193-21 1. Wiegersma, S. (1982a). A control theory of sequential response production. Psychological Research, 44, 175- 188.
Wiegersma, S. (1982b). Sequential response bias in randomized response sequences: A computer simulation. Acta Psychologica, 52, 249-256. Wiegersma, S . (1 984). Acoustic and semantic similarity effects on repetition avoidance in produced sequences. Memory and Cognition, 12, 190-194. Wiegersma, S., Van der Scheer, E., & Hijman, R. (1990). Subjective ordering, short-term memory, and the frontal lobes. Neuropsychologia, 28, 95-98. Winer, B. J. (1970). Statisticalprinciples in experimental design. New York: McGraw-Hill. Wingfield, A., Stine, E.A.L., Lahar, C.J., & Aberdeen, J.S. (1988). Does the capacity of working memory change with age? Experimental Aging Research, 14, 103- 107.
Wright, R. (1981). Aging, divided attention, and processing capacity. Journal of Gerontology, 36, 605-614. Yntema, D.B., & Trask, F.P. (1963). Recall as a search process. Journal of Verbal Learning and Verbal Behavior, 2, 65-74.
Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uear20
Subjective ordering, working memory, and aging a
Sjoerd Wiegersma & Karin Meertse
a
a
University of Utrecht Published online: 27 Sep 2007.
To cite this article: Sjoerd Wiegersma & Karin Meertse (1990) Subjective ordering, working memory, and aging, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 16:2, 73-77, DOI: 10.1080/07340669008251530 To link to this article: http://dx.doi.org/10.1080/07340669008251530
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
73
Experimental Aging Research, Volume 16, Number 2, 1990, ISSN 0734-0664 O1990 Beech Hill Enterprises Inc.
Subjective Ordering, Working Memory, and Aging SJOERDWIEGERSMA AND KARINMEERTSE
Downloaded by [Central Michigan University] at 15:00 31 December 2014
University of Utrecht
Cognitive decline in aging was studied by presenting four tasks involving short-term memory to young and old adults: digit span forward, missing scan, randomization span, and randomization span visual. Results showed that performance declined significantly with age in the latter two tasks, which require subjective ordering of a sequence of responses, and not in the first two tasks, which involve reproduction of a presented sequence and searching and comparison processes.
I
n reviews on age differences in adult human memory, Craik (1977) and Craik and Rabinowitz (1984) proposed that, whereas primary memory seems to remain intact with aging, there is a decline in the division of attention and the reorganization of material. A number of studies have documented the decline of performance with age in tasks requiring the division of attention among stimuli (Broadbent & Gregory, 1965; Parkinson, Lindholm, & Urell, 1980) or among competing operations (Broadbent & Heron, 1962; Gick, Craik, & Morris, 1988; Morris, Gick, & Craik, 1988; Wingfield, Stine, Lahar, & Aberdeen, 1988; Wright, 1981). The second aspect of the cognitive decline with age, reorganization of material, has been studied less widely. Reorganization of material taxes attentional capacity as opposed to passive repetition of material which poses minimal demands on attention. Hence, aging should affect the active processing aspects of working memory rather than the passive holding aspects (Gick et al., 1988; Morris et al., 1988). In the present study, four tasks involving short-term retention are presented to young and old adults. The four tasks all require the manipulation of numbers, but differ with respect to the degree and type of controlled processing and reorganization of material. The first task is digit span forward. Subjects are presented with random sequences of numbers of increasing lengths which have to be repeated immediately after presentation. This is assumed to have minimal requirements for reorganization of material, since subjects tend to repeat the sequence in the presented order. This is in line with findings that the digit spans of the aged are within the normal range of young adults, although at the lower end of the distribution (Parkinson, 1982). Digit span is mainly determined by passive recency effects and
the articulatory loop, which do not tax working memory capacity (Spinnler, Della Sala, Bandera, & Baddeley, 1988). In the present study, this task is mainly presented for the purpose of getting a baseline measure for comparison with the other three tasks requiring different types of processing. The second task is the missing scan. Random permutations of increasing sets of numbers (1-3, 1-4, etc.) are presented, in each of which one number is missing. It is the task of the subject to detect the missing item. In this task, the subject compares two sets of items: the set of designated numbers activated by instruction and those serially presented, searching the items of the first list while testing whether they are in the second (Buschke & Lenon, 1969; Yntema & Trask, 1963). This task requires the short-term retention of all numbers until the last item has been presented, as was the case in digit span forward. The task has low demands on active production processes and reorganization of material. Eventual differences on this task between young and old adults should be explained by the complexity of the comparison processes (searching and testing) involved. These processes are primarily based on recognition and, therefore, have low demands on retrieval and production, since only one single response is required (Buschke, 1963; Madsen & Drucker, 1966). The third task, randomization of a sequence of numbers, requires the production of all numbers of a set (1-3, 1-4, etc.) in a self-chosen ordering, with the explicit instruction not to produce any of these numbers twice or to use counting orders. This task requires the short-term retention of all produced numbers until the last number has been produced. It has been found in randomization, even when repetitions are not prohibited by instruction,
Correspondence and reprint requests should be addressed to Dr. S. Wiegersma, University of Utrecht, Vakgroep Psychonomie, Heidelberglaan 2, 3584 CS Utrecht, THE NETHERLANDS.
WIEGERSMA/MEERTSE
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that subjects tend to avoid repetition over distances of six or more items back in memory. A comparison mechanism, assuming short-term retention, can explain how such avoidance of repetition comes about (Wiegersma, 1982a, 1982b, 1984). One difference with the missing scan is clear: the order of the items in the missing scan is determined by the experimenter, whereas the randomization task requires ordering by the subject. This can be considered an instance of reorganization of material: the serially-ordered set of numbers must be subjectively reordered. The comparison processes in the randomization and missing-scan tasks are assumed to be approximately equal. However, some differences must be discussed. In the missing scan, comparison between designated and presented items is assumed to occur once, after all the items have been presented. In randomization, the subject must make a comparison of sets for every response made, with an increasing set of produced responses to compare with the designated ones when the sequence is growing. However, it seems reasonable to assume that in the latter task performance is determined by the last responses of the produced sequence, where the limits of performance are approached. The responses produced earlier in a sequence are easier to find, since fewer comparisons with earlier responses are required. Moreover, they are no burden for producing later responses. On the contrary, the extra comparisons made for earlier responses might provide extra practice in the randomization task, resulting in better performance with later responses. It is not clear whether or not subjects make such early comparisons in the missing scan, where no response is required until the last item has been presented. In conclusion, the comparison processes in randomization do not seem more difficult than those involved in the missing scan task. The difference between both tasks is in the additional load on reorganization of material in the randomization task. The fourth task, randomization-visual, is identical to the third, except that with each vocal response production all choice alternatives are presented to the subject in a different visual arrangement. Such a task was originally used by Petrides and Milner (1982) in a study of the cognitive disorders of frontal-lobe patients. Our task differs from theirs in that the choice alternatives are numbers and in the use of vocal responses rather than pointing responses. The subject has to select one number response from each sheet of paper, while the experimenter turns them over, and has to avoid repetition and counting orders. The difference with randomization is small. In randomization, the responses have to be selected from a memory set of responses which remains continuously activated during production of the sequence. In randomization-visual, such a memory representation does not seem to be required, since the choice alternatives are presented at each trial. However, since the alternatives are presented in a new arrangement at each trial, subjects seem to use a memory set of choice alternatives, just as they do in randomization, rather than relying on the vicissitudes of the visual display.
In summary, the digit span is assumed to measure storage capacity with low demands on processing capacity, the missing scan measures comparison processes in addition to storage capacity and the randomization tasks measure reorganization of material in addition to the processes involved in the other tasks. If there is a decline with age in the search for and comparison of information, differences between old and young adults should show up in missing scan as well as randomization. If the decline is due to reorganization of material, only the two randomization tasks should be affected by age.
Method
Design Four experimental tasks were presented to groups of young and old adults: digit span forward, missing scan and two subjective ordering tasks: randomization span and randomization span visual. The tasks were presented to 12 young adults and 12 older adults, in an order determined by latin squares providing balanced counterbalancing (Edwards, 1968, pp. 191-193). After these tasks had been completed, two additional tasks, digit span backward and word fluency were presented. Both of these tasks require sequential reorganization by the subject. Digit span backward was considered interesting because of previous findings of aging effects in this task, as contrasted with digit span forward (Bromley, 1958). Word fluency was tested with semantic categories (animals and professions) and initial letters (S, M and K).Subjects had to produce as many words of each type as they could within one minute. Aging effects on word fluency tasks have generally been found (e.g. , Howard, 1980; Schonfield & Stones, 1979).
Subjects Twelve young adults (mean age: 23.8 yrs; range: 16-33 yrs) and 12 aged adults (mean age: 70.7 yrs; range: 63-79 yrs) participated. There were six men and six women in the group of young adults and seven men and five women in the group of aged adults. The groups differed in the degree of educational level: mean years of education were 12.6 in the young and 8.6 in the aged group. In evaluating differences between age groups, this confounding of age and educational level was accounted for by treating the latter variable as a covariate in the analysis.
Procedures All four experimental tasks rely heavily on short-term memory and involve the use of numbers. The tasks differ in the extent to which they require control processes and attention. Digit span forward. A subset of the numbers 1- 12 was presented aurally at a rate of one number per second, for immediate recall by the subject. The first sequence consisted of three numbers, followed by four, five, etc. One
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additional three-number trial served as practice for the subject. For comparability with the other tasks free recall, rather than the usual ordered recall was allowed (Buschke, 1963). When no errors were made, there was one trial at each level. In the case of an error, the subject did an additional trial at the same level. The subject earned three points if the first level of three numbers was successfully completed and one additional point for each first trial of a higher level performed correctly, and 0.5 point for the correct performance of a second trial. If both trials at one level were wrong, testing was stopped. Missing scan. Random sequences of n-1 numbers, randomly selected from sets of n numbers, were presented to the subject at the rate of one per second. Set size (n) was gradually increased from 3 (numbers I-3), through 4 (1-4), etc., until the subject failed to mention the missing number. There was one trial at each level as long as the subject was correct. In the case of failure, an additional trial at the same level was performed. Scoring was as for digit span. Randomization. Subjects had to select responses from increasing sets of numbers (1-3, 1-4, etc.) in a self-chosen ordering, until they produced a sequence in which one or more repetitions occurred. In addition to that, subjects were required to avoid counting orders (e.g., ‘3,4’). If the subject used such stereotyped order despite the instruction he/she got an additional trial at the same level, after the instruction to avoid counting had been repeated. Violation of this requirement in subsequent trials was counted as an incorrect trial. At each trial a randomly chosen number was given to the subject to start with. In order to avoid too high requirement on speed, especially for the aged, subjects were allowed to produce the sequence at a self-paced rate. Randomization-visual. This task was identical to the randomization task, except that all choice alternatives were presented to the subject in a different visual arrangement with each vocal response production. A comparable task, but requiring pointing rather than verbal responses, has been used by Petrides and Milner (1982) and Wiegersma, Van der Scheer and Hijman (1990) for the study of patients with frontal-lobe lesions. The subjects selected one of n alternative numbers from sheets of paper, while the experimenter turned them over at a rate determined by the speed of production of the subject. The instructions and scoring were the same as in the randomization task. All four tasks started with one practice trial at level three. For the last three tasks, the relevant set of responses of each trial was presented aurally as well as visually on a card, which was turned over before the trial started.
Materials The numbers 1-12 were used in all four tasks, except the missing scan in which four extra levels were prepared (up to the numbers 1-18), because of the higher spans found on this task.
12
r-
10
I
I
I
I
i
-
C
a a
a-
cn 6-
1 DS
T
MS a s
R k
RV
FIGURE 1. Mean span scores of young and old adults at four tasks involving short-term memory. DS = diglt span, MS = misslng scan, R = randomization, and RV = randomization visual.
Results Experimental Tasks Mean spans of the two age groups are shown in Figure 1 . An analysis of covariance with repeated measures over tasks and level of education as a covariate (Winer, 1970, pp. 606-618) showed a significant effect of age group (F [1,21] = 14.98, p < .025), of task, (F [3,66] = 69.89, p < .025) and a significant interaction effect of group with task (F [3,66] = 3.49, p < .025). Separate analyses of covariance for each task showed significant group differences for randomization (F[1,21] = 6.83, p < .025) and randomization-visual (F[ 1,211 = 1 1.70, p < .025), but not for digit span and missing scan (I,> .05 in both cases). The proportions of variance accounted for by the experimental treatments (q*)in these analyses are 14.8% for digit span, 15.7% for missing span, 32.4% for randomization, and 55.8% for randomization-visual. That level of education was not responsible for the differences in subjective ordering between groups was further supported by the lack of correlation of this variable with randomization (r = - .02 and - .21 for the young and the aged respectively,) and randomization-visual(r = .08 and . l 1 for the young and the aged respectively).
Backward Span and Word-Fluency Tasks Backward span was lower for the older adults (M = 4.25, SD = .62) than for the younger adults (M= 4.96,
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WIEGERSMA/MEE:RTSE
SD = .62), as shown by an analysis of variance (F[ 1,221 = 7.81, p = .Ol), but the difference was almost entirely due to the difference in educational level between the groups as shown by an analysis of covariance in which the covariate educational level was significant (F [1,21] = 6.93, p = .02), leaving a nonsignificant effect due to age. Word-fluency scores were lower in the older than in the younger adults (the mean numbers of words produced were 16.8 (SD = 2.4) vs. 21.5 (SD = 3.0) for categories, and 11.0 (SO = 6.3) vs. 17.6 (SD = 4.0) for letters). The effect of age for both scores together was significant as shown by an analysis of covariance (F[1,21] = 4.60, p < .05), and so was the effect of the covariate level of education (F [1,21] = 12.37, p < .01). Correlations Bet ween Tasks Correlations between tasks were calculated in order to get an estimate of the degree to which the tasks measure shared processes (Table 1). Correlations with age partialled out are shown in parentheses in the same table. The missing scan only correlated with digit span forward and not with any of the other tasks. The subjective ordering tasks both correlated significantly with the word fluency tasks and with digit span backward. After age was partialled out, intercorrelations between tasks tend to disappear.
Discussion The results are as predicted: performance of older subjects is reduced relative to younger subjects when tasks require active production. No differences between age groups are found when tasks require minimal production (the missing scan) or simple recall of a sequence (the digit span forward). It is not the degree to which production is involved which determines the aging effect, but the extent to which production requires active ordering by the subject.
The active ordering required by these tasks consists of at least two components, a comparison process leading to the finding of nonrepetitions and the selection and monitoring of responses. The comparison process does not seem responsible for the decline with age in subjective ordering, since the missing scan shows highly intact performance. This finding is in line with the general notion that the cognitive decline with age is due to reduced attentional processing capacity, while the automatic processes would remain intact. The remaining component, response selection and monitoring, must be responsible for the aging effect in the subjective ordering tasks. This involves first, the selection of candidate responses from the nonrepetitions which are output of the comparison process, and second, monitoring of the selected response. The monitoring process is required for the suppression of counting orders. It has been found that counting orders in randomization increase with larger sets of choice alternatives and simultaneous performance of a second task, presumably due to limited processing capacity (Wiegersma, 1982a). In conclusion, our results are in line with Craik and Rabinowitz’ (1984) hypothesis that reorganization of material declines with age. However, we suggest that it is the selection and monitoring component rather than the comparison component of reorganization which declines. The absence of an aging effect on digit span forward confirms earlier findings, but there was no effect of age on digit span backward. We found a group difference in the latter task, but it was no longer significant when educational level was partialled out. Bromley ( 1 958) found a reliable difference between age groups matched for educational level, but the difference was small (0.5 as compared to 0.7 in this study) and based on a large number of subjects (200). The differences between young and old adults are substantially larger in randomization (1.9) and randomization visual (3.0). The absence of an age difference in the missing scan might seem somewhat surprising, since the main determinant of performance is supposed to be search and com-
TABLE 1 Product-Moment Correlations Between Tasks (in parentheses: correlations with age partialled out), Over All 24 Subjects
DS
MS
.42* (.36) .57* (.49*) .30 (.07) .46* (.35) .36 (.17) .40 (.25)
.25 (.15) .15 (-.04) . I 5 (.01) .10 (-.lo) .27 (.16)
R
RV
~~
MS R RV Backward Span Word Fluency - C. Word Fluency - L.
.57* (.32)
.58* (.41) .51* (.24) .50* (.28)
Note. DS = digit span forward; MS = missing scan; R = randomization; RV= randomization visual. * p < .05, two-sided test.
.54*
(.24) .47* ( - .07) .61* (.32)
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parison in short-term memory. Such processes have also been studied with binary-classification RT tasks and showed effects of aging. The time for comparison was found to be longer when people get older (Anders & Fozard, 1973; Anders, Fozard, & Lilliquist, 1972; Madden & Nebes, 1980). However, although the search and comparison processes may be comparable in both tasks, an important difference might be that the RT task puts great emphasis on speed, which is not critical in the missing scan. Madden and Nebes (1980) showed that, while comparison time increases, the number of errors made by the subject does not increase with age, when both speed and accuracy are stressed equally by instruction. So, these results are not necessarily in contradiction with our results in the missing scan task, which requires accuracy rather than speed.
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