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Psychology and Aging1992, Vol. 7, No. 2, 242-251
Copyright 1992 by the American Psychological Association, Inc.0882-7974/92/S3.00
Improving Memory Performance in the AgedThrough Mnemonic Training: A Meta-Analytic Study
Paul Verhaeghen, Alfons Marcoen, and Luc GoossensCenter for Developmental Psychology
University of Louvain (Katholieke Universiteit Leuven), Belgium
The effectiveness of memory training for the elderly was examined through a meta-analysis ofpre-to-posttest gains on episodic memory tasks in healthy subjects aged 60 or above. Pre-to-post-test gains were found to be significantly larger in training groups (0.73 SD, k = 49) than in bothcontrol (0.38 SD, k = 10) and placebo (0.37 SD, k=S) groups. Treatment gains in training groupswere negatively affected by age of participants and duration of training sessions and positivelyaffected by group treatment, pretraining, and memory-related interventions. No differences intreatment gain were obtained as a function of type of mnemonic taught nor the kind of pretrainingused.
An important topic in recent psychogerontological researchis the modifiability of older adults' cognitive functioningthrough relatively brief experimental interventions (Hultsch &Dixon, 1990; Willis, 1990). One line of research has specificallyinvestigated the plasticity of memory performance through in-struction in mnemonic techniques such as the method of loci,the name-face mnemonic (McCarty, 1980), or the pegwordmnemonic (for an overview of mnemonics, see Belezza, 1983).
In this article, we present an overview of more than a decadeof intensive research on memory training with the elderly, usingmeta-analysis as a quantitative tool for literature review. Morespecifically, three questions guided our research: (a) What is themagnitude of the effect obtained as a result of mnemonic train-ing? (b) Which (quantifiable) characteristics of both sample andstudy design are associated with this effect? (c) Are there anydifferences in the effect magnitude associated with the type ofmnemonic taught or the type of pretraining used?
Usually, a meta-analysis is carried out by contrasting theposttest performance of a treatment group with the retest per-formance of a no-treatment control group. In this article, wedepart from this custom, using pretest-posttest gains in perfor-mance of treatment groups, and comparing those with the test-retest gain in performance of no-treatment control groups andplacebo groups. Three main reasons incited us to use treatmentgain as the focus of this study.
Portions of this research were presented at the Xlth Biennial Meet-ings of the International Society for the Study of Behavioural Develop-ment, Minneapolis, Minnesota, July 1991, and the Fifth Congress ofthe International Psychogeriatric Association, Rome, August 1991.
This research was conducted while Paul Verhaeghen was a researchassistant at the National Fund for Scientific Research, Belgium. Part ofthe investigation was supported by a grant from the Prof. Dr. Jan Hel-lemans Fund, Belgium.
We are highly indebted to three anonymous reviewers for their con-structive comments on an earlier version of this article.
Correspondence concerning this article should be addressed to PaulVerhaeghen, Center for Developmental Psychology, Tiensestraat 102,B 3000 Leuven, Belgium.
First, there is a conceptual reason for considering treatmentgain rather than posttest differences between groups. Themain focus in memory training research is plasticity—therange of intraindividual differences—in memory functioningin old age (Hultsch & Dixon, 1990; Willis, 1990). This range ofintraindividual change is exemplified in treatment gain and notin a comparison of trained versus merely retested individuals atposttest.
Second, we tried to arrive at a representative sample of therelevant literature. Because the majority of memory trainingstudies with the elderly (i.e., 70% of the sample presented here)do not include comparisons with a no-treatment control group,classical meta-analysis would severely limit the number of datapoints. Moreover, some of the most influential studies (e.g.,cited in the review articles by Hultsch & Dixon, 1990, and Yesa-vage, Lapp, & Sheikh, 1989), notably those of Kliegl and asso-ciates and those of Yesavage and associates, have only rarelyincluded control groups. Using classical meta-analytic proce-dures would necessitate that these important studies be dis-carded from the analysis.
Third, focusing on treatment gain rather than control-treat-ment comparisons allows one to include more than one treat-ment group per study in the analysis, thus further increasingthe number of data points. The statistical procedures that weuse (including multiple regression) require stochastic indepen-dence of the effect sizes used for computations. In studies thatinclude more than one treatment group (this was the case for42% of the studies in the present sample), classical meta-ana-lytic procedures necessarily create an unknown degree of de-pendence, because all treatment groups are compared with acommon control group. This problem does not occur whenanalyzing treatment gains.
Method
The Sample of Studies
To identify relevant studies, we used the CD-ROM databases ERICand PsycLit and manually searched Dissertation Abstracts Interna-
242
IMPROVING MEMORY IN THE AGED 243
tional, using terms such as mnemonics and strategies-learning on theone hand and elderly and gerontology on the other hand. Referencescited in the selected studies were used to identify studies not includedin the original sample. Some European studies were kindly made avail-able to us through personal contacts with research departments in thatpart of the world.
Included in the final sample were studies that (a) included healthynormal subjects with a mean age of 60 or over who were free fromcognitive problems caused by organic pathology, (b) aimed at the im-provement of memory performance through instruction in some mne-monic technique, (c) included a pre- and posttreatment measure ofmemory performance (studies that investigated long-term effectsthrough follow-up were not included), and (d) provided sufficient sta-tistical data for the computation of effect sizes. A total of 31 researchpapers were retrieved, including 33 studies.
The total sample of older subjects consisted of 1,539 persons, with anestimated mean age of 69.1 years. (Mean age was estimated from mid-point of age range for those studies in which mean age was not re-ported.)
Coding of Variables
Each group included in these studies was coded as being either (a) acontrol group, when no treatment (apart from testing) was given; (b) aplacebo group, when treatment did not include the teaching of mne-monics; or (c) a mnemonic-training group, when at least one mne-monic was taught. Ten groups were classified as being control groups,8 as being placebo groups, and 49 as involving mnemonic training.Placebo treatment was diverse and consisted of giving feedback, doingexercises to enhance attention and concentration, teaching relaxationtechniques, discussing personal and memory problems, and providingsubjects with information about memory and aging. The sample ofgroups (along with some of their characteristics) is listed in Table 1.
Studies were scanned for variables that might influence pre-to-post-treatment gains. Variables for which values could be coded for thewhole sample of mnemonic-training groups were included in a regres-sion analysis designed to answer our second research question. In total,13 variables were identified. Descriptive statistics for each of thesevariables are provided in Tables 2 and 3.
Five of the variables (see Table 2) were continuous: (a) age of subjects,(b) pre-to-posttest interval, (c) end of training-to-posttest interval, (d)number of training sessions, and (e) session duration. Eight variables(see Table 3) were coded in dummy format (O/1): (a) teaching of a singlemnemonic versus multiple mnemonics, (b) inclusion of pretraining, (c)additional memory-related (but nonmnemonic) intervention, (d) in-struction by a real-life tutor versus instruction solely through manualsor tapes, (e) individual versus group sessions, (f) unpublished versuspublished study, (g) inclusion of a control group in the design, and (h)recruitment of subjects for an unspecified experiment versus recruit-ment for a memory-improvement program.
Interventions before training were coded as being a pretraining whenone or more sessions of nonmnemonic intervention were provided,specifically intended to increase benefit from mnemonic instruction.In the present sample, pretraining consisted of relaxation training,training in visual imagery formation and elaboration, teaching of ajudgment technique (judging the pleasantness of visual image associa-tions), or a combination of the latter two techniques. It may be addedhere that interventions before the training phase that were not in-tended to enhance treatment gain—that is, programs to improve atti-tudes toward aging (Yesavage, 1983, 1984)—were not coded as pre-training. Yesavage himself considered these groups to be referencegroups rather than pretraining groups.
In the present sample, memory-related interventions consisted oftreatments as diverse as concentration and attention training, teaching
of external memory techniques, providing information about memoryand aging, group discussion, relaxation training, working on personalinsights, training in self-monitoring, motivation enhancement, offer-ing feedback, and teaching problem-solving skills.
One important variable, years of education, was only reported in 19of the studies (30 treatment groups), so this variable was analyzedseparately.
Meta-Analysis
Generally speaking, meta-analysis can be defined as the statisticalintegration of the results of independent studies. The analysis typicallycomprises two steps: (a) the calculation of effect sizes from the resultsof individual studies and (b) the statistical analyses proper, which aredesigned to account for the observed variability in the results obtainedin the primary studies. In this study, we used a modification of themeta-analytic procedures advocated by Hedges and Olkin (1985). Thismethod is sometimes referred to as "approximate data pooling withtests of homogeneity" (Bangert-Drowns, 1986, p. 394). Modificationspertained to the first step in the procedure (calculation of effect sizes)only and basically involved a shift from the traditional between-groupsapproach (experimental vs. control group) to a within-group approach(pre- vs. posttest) as discussed in the introduction.
Calculation of effect sizes. In this initial step of the meta-analysis,the pre-to-posttest improvements of different groups are expressed ona common metric to make them comparable. The statistic used for thispurpose was J. Cohen's (1977) d or the standardized mean difference.In the present analysis, the pretest mean was subtracted from the post-test mean for each group (mnemonic training, control, or placebo), andthe resulting difference was divided by the pooled standard deviationfrom both test occasions (pretest and posttest). This approach repre-sents a departure from traditional procedures in the meta-analysis ofintervention research that use the posttest difference between meansof the experimental and comparison group (control or placebo) di-vided by the pooled standard deviation (across both groups) as thepreferred measure for effect size. Whenever summary statistics werenot reported in the primary source, effect sizes were derived frominferential statistics (Fand;), taking the formulas suggested by Smith,Glass, and Miller (1980, Appendix 7) as guidelines.
All of the d values obtained were corrected for small sample biasusing the Hedges and Olkin (1985) correction factor. In addition to thecorrected d value (called d,), essentially a point estimate of the popula-tion effect size, a confidence interval was obtained for each of theindividual effect sizes.
It may be noted here that only one effect size was eventually retainedfor each of the 67 groups (training, placebo, or control) entered in thepresent meta-analysis. When several memory measures were used forasingle group, every effort was made to derive direct tests of trainingimpact, taking into account both the mnemonic taught and the mem-ory task used as an evaluation measure. To this end, a distinction wasmade between target and nontarget memory measures. A memorymeasure was considered to be a target measure when the newly ac-quired mnemonic could be applied on this task and a nontarget mea-sure when the mnemonic taught could not be applied. Effect sizes werecalculated for target measures only and averaged whenever there wasmore than one of them for the same group of subjects.
Examples for studies that taught a single mnemonic may clarify thisgeneral principle. For the method of loci, for example, performance ona list of concrete words was considered a target measure and the resultsfor that measure were expressed as an effect size. If there were threedifferent list tests, the resulting effect sizes were averaged. Any paired-associate task, name-face-association task, prose recall task, or short-term memory task administered to the groups of subjects who weretaught the method of loci was considered a nontarget measure, and the
244 P. VERHAEGHEN, A. MARCOEN, AND L. GOOSSENS
Table 1Studies Included in the Meta-Analysis
95% confidencelimits for dt
Study n Mean age 4 Lower Upper
Control groups
DeLeon(1974)Fly nn&Storandt( 1990)Loonen & Richter (1988)Meyer, Young, & Bartlett (1989)Pratt (1981)Rebok&Balcerak(1989)»Robertson-Tchabo, Hausman,
& Arenberg (1976, Study II)Schaffer&Poon(1982)1
Scogin, Storandt, & Lott (1985)Stokvis(1988)b
81915181112
10172727
72.269.762.269.467.667.8
70.772.966.872.0
0.090.270.610.340.240.14
0.760.570.210.55
-0.89-0.37-0.12-0.32-0.60-0.66
-0.14-0.12-0.33
0.00
1.070.911.351.001.080.95
1.671.250.741.09
Placebo groups
DeLeon(1974)Hill, Sheikh, & Yesavage (1987)Meyer etal. (1989)Pratt (1981)Rebok&Balcerak(1989)Schaffer&Poon(1982)Yesavage, Rose, & Bower (1983)"Zarit, Gallagher, & Kramer (1981)'
817131012172121
73.567.567.768.667.872.965.663.7
-0.020.240.690.100.430.250.031.10
-1.00-0.43-0.12-0.77-0.38-0.43-0.58
0.45
0.960.921.490.981.240.920.631.75
Memory-training groups
Anschutz, Camp, Markley, & Kramer (1985)Deelman, Koning-Haanstra, & Berg (1990)DeLeon(1974)Flynn(1987)
Self-instructionSelf-instruction and group discussion
FlynnA Storandt (1990)Self-instructionSelf-instruction and group discussion
Gratzinger, Sheikh, Friedman, & Yesavage (1990)ImageryRelaxationImagery and judgment
Hill etal. (1987)Hill, Yesavage, Sheikh, & Friedman (1989)Kliegl, Smith, & Bakes (1989)
Study 1Study 2
Lane (1984)Memory trainingMemory training and memory-skills training
Loonen & Richter (1988)Markel(1982)Meyer etal. (1989)Pratt (1981)
TrainingTraining and motivation
Rebok&Balcerak(1989)"TrainingTraning and feedback
Robertson-Tchabo et al. (1976)Study IStudy II, lociStudy II, loci and directions
Rose & Yesavage (1983)Schaffer&Poon(1982)"Scogin etal. (1985)Stokvis(1988)b
Verhaeghen (1989)
1068
3130
1821
56505059
102
2019
1111163021
1110
1111
5101026172025
7
71.064.070.9
69.268.9
66.767.9
68.068.568.867.875.4
71.771.7
72.970.864.173.769.0
68.567.0
67.867.8
69.370.671.761.472.966.572.066.8
0.611.300.14
0.561.04
0.340.96
1.060.890.750.740.09
1.851.06
0.430.430.480.521.06
0.640.59
1.111.07
0.341.071.320.800.620.530.280.72
-0.290.05
-0.84
0.050.50
-0.320.32
0.670.480.350.36
-0.19
1.110.38
-0.41-0.41-0.22
0.010.42
-0.21-0.31
0.210.18
-0.910.130.350.24
-0.07-0.10-0.28-0.36
1.502.551.12
1.071.58
1.001.60
1.461.301.161.110.36
2.591.74
1.281.281.181.041.71
1.501.48
2.011.97
1.592.012.291.371.311.160.841.80
IMPROVING MEMORY IN THE AGED 245
Table 1 (continued)
Study n Mean age
95% confidencelimits for d>
Lower Upper
Memory-training groups (continued)
Yesavage (1983yImageryAttitude improvement
Yesavage(1984)il
RelaxationAttitude improvement
Yesavage & Jacob (1984)Yesavage& Rose (1983)"
LociLoci and concentration
Yesavage & Rose (1984a)Yesavage & Rose (1984b)a
LociLoci and judgment
Yesavage etal. (1983)"Name-faceName-face and judgment
Yesavage, Sheikh, Friedman, & Tanke (1990)ImageryRelaxationImagery and judgment
Yesavage, Sheikh, Tanke, & Hill (1988)"JudgmentRelaxation
Zarit etal. (1981)
2525
191925
191622
2017
2118
746777
202020
78.078.0
71.671.674.2
68.768.761.4
66.266.2
65.665.6
67.767.967.6
67.067.063.7
0.610.16
0.660.131.82
0.281.131.07
0.131.25
0.950.95
0.850.681.11
1.140.880.99
0.05-0.39
0.01-0.51
1.16
-0.360.380.44
-0.490.52
0.310.26
0.510.330.78
0.470.230.34
1.180.72
1.310.762.48
0.921.871.70
0.751.99
1.591.64
1.181.031.45
1.801.531.65
Note. dt = point estimate of effect size.* Mean age reported is the mean age for all groups combined.age range.
b Mean age was estimated by midpoint of
results pertaining to these tasks were simply dropped from the analy-sis. Conversely, name-face-association tasks were considered targetmeasures for the name-face mnemonic, and only the effect sizes forthis type of task (averaged whenever appropriate) were entered into themeta-analysis, discarding all results pertaining to other types of mem-ory tasks. Comparable decisions were made for groups that weretaught multiple mnemonics (with all memory tasks on which any of themnemonics taught could be used considered as target measures) andfor control and placebo groups (with decisions on target and nontargetmeasures that paralleled those for the corresponding training groupwithin a given study).
The procedure just briefly outlined ensures that results for target
Table 2Descriptive Statistics for Continuous Variables Coded forMemory-Training Groups (k = 49)
Continuous variable M SD Min. Max.
Age (years)Pre-to-posttest interval
(days)Training-to-posttest
interval (days)No. of sessionsDuration of sessions (hr)
68.99
22.64
2.335.761.49
3.57
23.65
2.735.120.56
61.35
0.08
0.001.000.33
78.00
91.00
14.0020.002.50
measures (direct tests of training impact) are not simply lumped to-gether with results for nontarget measures (tests for generalization oftraining), which would presumably bias against a strong training ef-fect. One additional advantage of meta-analysis is that the latter as-sumption—stronger impact on direct tests as compared with general-ization tests—may be empirically examined in additional analyses.For 10 training groups, a clear distinction could be made betweentarget and nontarget measures, and their respective effects were com-pared directly.
Table 3Descriptive Statistics for Variables Coded in Dummy Format(0/1) for Memory-Training Groups (k = 49)
Dummy variable Coding %ofls
Note. Min. = minimum; Max. = maximum.
Single vs. multiplemnemonics
PretrainingMemory-related
interventionsReal-life tutor vs.
manual/tapeGroup sessionsPublication statusInclusion of control groupRecruitment for memory
training
Single/multipleNo/yes
No/yes
Tutor/no tutorNo/yesPublished/unpublishedNo/yes
No/yes
6575
65
86172270
53
3525
35
14837830
47
246 P. VERHAEGHEN, A. MARCOEN, AND L. GOOSSENS
Statistical analyses. As a result of the first step in the meta-analyticprocedure, a sample of effect sizes is obtained to which a series ofstatistical techniques can be applied, each of which can be likened towell-known techniques in primary data analysis. An average effect sizecan be computed for the whole sample and a confidence interval estab-lished. Furthermore, the variability in effect magnitude observed inthe sample may be analyzed by means of procedures that closely resem-ble standard analysis of variance (ANOVA) and regression techniques.The particular techniques used to answer the three research questionsof the present article are briefly discussed.
Comparing treatment gain versus retest and placebo effects (Re-search Question 1) involves a multistep approach. A weighted averageeffect size is computed for the entire sample in which results based onlarger samples are given greater weight. One may then test whether thisaverage effect is significantly different from zero by delimiting a confi-dence interval around the observed mean value. An additional statis-tic allows one to test whether the whole sample of effect sizes is homoge-neous, that is, whether the observed effect can meaningfully be repre-sented by means of a single value (the average effect size). If thehomogeneity statistic (QT, which is x2 distributed with k-\df, where kstands for the number of effect sizes) exceeds the critical value, addi-tional analyses are called for.
The overall sample of effect sizes is then broken down into smallergroupings (or classes) according to a priori categorical dimensions.The principle of variance partitioning, well-known from its applica-tion in the ANOVA, is applied in the analysis of the original nonhomo-geneity of the entire sample. The total estimate of the variability «2T) isbroken down into a single between-groups homogeneity index ((?„)and a series of within-group homogeneity indices (gw), one for each ofthe different groupings of effect sizes. The QB statistic (x2 distributedwith p - 1 df, where p stands for the number of groupings or classes) isroughly similar to an omnibus F test; QB tests whether the averageeffect sizes in each of the groupings are significantly different fromeach other. When there are more than two groupings or classes, asignificant QB statistic may be followed up by Bonferroni or Scheffetests. Each of the (?w statistics (x2 distributed with k,- \ df where ̂stands for the number of effect sizes in the fth grouping) tests whetherthe variability within each of the groupings is entirely due to samplingvariation. The best possible result is obtained when the QB statistic issignificant and each of the (?w statistics is nonsignificant. The originalnonhomogeneity of effect sizes for the entire sample (QT) has thenbeen accounted for by the variability as a function of the categoricaldimension under study.
Examining the effect of a whole set of study characteristics on effectmagnitude (Research Question 2) naturally calls for regression analy-ses. The appropriate meta-analytic technique is a least squares analysiswith two distinctive features, (a) Each observation is weighted by theinverse of variance of the effect size estimate. The rationale behind thisweighing procedure is that the variances of the individual effect sizeestimates, which are inversely proportional to the sample sizes of thestudy, can be dramatically different, particularly when differences insample size tend to be rather large, (b) An additional test statistic,known as the error sum of squares statistic (QE) provides an explicittest of the goodness of fit of the regression model. When this statistic(x2 distributed withk- p-\df where k stands for the number of effectsizes, and p for the number of predictors) does not exceed the criticalvalue, the regression model adequately explains the observed variabil-ity in effect size estimates.
Finally, comparing the effectiveness of different kinds of mnemon-ics and different types of pretraining (Research Question 3) essentiallyinvolves the same meta-analytic techniques as discussed for the firstresearch question. If the total variability ((?T) proves nonsignificant,the effect sizes may simply be averaged across types of mnemonic orpretraining, respectively. Alternatively, QT may be significant, and
both between (QB) and within ((?w) homogeneity indices may be com-puted to determine if some types of mnemonic or pretraining yielded alarger effect than others and whether the groupings of effect sizes foreach of the different mnemonics or types of pretraining were homoge-neous.
In summary, then, larger groupings of effect sizes are broken downinto ever smaller subsamples or classes until each of them is homoge-neous and represents a single population treatment effect, whereas—inthe best of possible cases—their average effects are significantly dif-ferent from one another.
Results
Treatment Gain Versus Retest and Placebo Effects
The weighted average effect size for the entire sample (k=61)was 0.66, a value that is significantly different from zero (95%confidence interval: 0.59 to 0.74). The homogeneity statistic,however, was significant and rather large (QT = 110.99, p < .05),necessitating additional analyses that contrasted training, con-trol, and placebo groups.
Results of these analyses are presented in Table 4. Three dif-ferent analyses are reported, and three findings are noteworthyhere. First, it can be seen that the elderly benefited more frommnemonic training than from either control or placebo treat-ments. There was significant nonhomogeneity between thethree classes (QB), and analysis of pairwise contrasts (using theHedges & Olkin, 1985, analogue of the Bonferroni procedure)showed that the effect size for memory-training groups wassignificantly different from that of control and placebo groups,which did not differ from each other (z = 2.96, 2.59, and 0.04,respectively, tested against a critical value of 2.40). So there wasan effect that was specific to mnemonic treatment.
Note also that the average effect size for memory-traininggroups was heterogeneous, as might be expected when a sampleof studies using many different kinds of treatment is consid-ered. In this vein, it is reassuring to find that effect sizes forcontrol and placebo treatment were homogeneous. This indi-cates that all control or placebo groups can be considered asbeing replications of each other.
Second, a direct comparison between control groups andexperimental groups in those studies that included both alsoresulted in a significant between-groups difference favoring ex-perimental groups.
Third, there appeared to be a difference between effect sizesfor target and nontarget measures in those studies where thesetwo types of measures could be distinguished: There was al-most no overlap in the respective confidence intervals for thetwo average effect sizes. (Because these measures were takenfrom the same subsample of studies, the effect sizes were sto-chastically dependent. As a consequence, the significance ofthe differences between these two effect sizes could not betested directly) So the effect of mnemonic training appears tobe specific, being larger for those memory tasks that allowedfor the use of the newly acquired mnemonic.
Treatment Gain as a Function of Selected StudyCharacteristics
Our second research question pertained to the variables thatmight influence pre-to-posttreatment gains in memory perfbr-
IMPROVING MEMORY IN THE AGED 247
Table 4Summary of Effect Size Statistics (Effects of Memory Training as Compared With Control andPlacebo Groups and Effects on Target and Nontarget Measures)
95% confidence limitsfor<sf+
Measure Lower Upper
Total sampleControlPlaceboMemory training
Studies including acontrol condition"
ControlMemory training
Target versus nontargetmeasures'"
TargetNontarget
108
49
1014
1010
.38
.37
.73
.38
.68
.64
.24
.16
.12
.65
.16
.48
.43
.03
.60
.63
.82
.60
.88
.84
.44
3.027.91
86.03
3.0210.81
7.565.75
Note. QB = 14.03 and 3.99, respectively, for total sample and studies including a control condition, withsignificant nonhomogeneity at p < .05, according to chi-square tests, for both, k = number of effect sizes;d+ = mean weighted effect size; Q, = chi-square statistic for homogeneity within groups; QB = chi-squarestatistic for homogeneity between groups.* Because in some of these studies more than one training group was compared with a control group, thenumber of training groups exceeds that of control groups. b Because of stochastic dependency of thesubsamples, QB cannot be computed.
mance in memory-training groups. It is possible (even probable)that there existed some multicollinearity between the 13 pre-dictors mentioned earlier. We decided to tackle this problem inan empirical way, rather than excluding any of these 13 vari-ables on an a priori basis from the regression analysis. Theresults of the regression analysis that was carried out to thiseffect are shown in Table 5.
Results of two analyses are presented in the table. In a firstanalysis (the full model), all variables were entered in the equa-tion (upper part of Table 5). In a second analysis (the derivedmodel), the equation was reevaluated with only the significantpredictors from the first equation as independent variables.Both models adequately fit the data (as indicated by the nonsig-nificant Qe values).
To detect problems caused by multicollinearity, each inde-pendent variable was regressed on all the remaining ones; thejR2 of this regression can be taken as an index for multicollin-earity (Berry & Feldman, 1985). In the full model, these R2swere rather high for some variables, as can be seen in Table 5.This indicates that there was some interdependence in the setof predictor variables. In the derived model, however, multicol-linearity did not play a major role. The alternative way of trim-ming the full model by eliminating variables that were responsi-ble for multicollinearity resulted in estimations close to thoseof the derived model: No predictor other than those that werealready significant in the full model became significant in thetrimming process, and the variable memory-related interven-tions became nonsignificant when the model was trimmed tomake all R2s smaller than .64 (so that all Rs were smallerthan .80).
It can be seen that in both models presented in Table 5 age ofparticipants and duration of sessions had a negative impact oneffect magnitude, whereas the presence of pretraining and
group training had a positive impact. In the full model, therewas also a positive effect of memory-related interventions.
Education was another possibly important mediator vari-able. However, a median split off (at 14 years of education) failedto yield a significant between-groups difference (low educa-tion: 0+ = 0.81, k = 12; high education: d+ = 0.82, k = 15;<2B=0.01).
Types of Mnemonics and Pretraining
Our third research question pertained to differences asso-ciated with type of mnemonic taught and type of pretraining.
Comparison of the effectiveness of different mnemonics wasrestricted to the groups that were taught a single mnemonic (k=31). The homogeneity index proved nonsignificant for this sam-ple as a whole (QT = 39.05, ns). It may be concluded, therefore,that the average effect size for this subsample of training groupswas 0.81 (95% confidence interval: 0.70 to 0.92) and that therewas no need to account for variability in effect sizes as a func-tion of the type of mnemonic taught. For purely illustrativepurposes, the effectiveness of different types of mnemonics isshown in Table 6.
A quick glance at the table reveals that differences in effectsize between the different types of mnemonics were nonsignifi-cant. It may be noted that, except for organization, all mne-monics taught in the present sample of training groups involvedimagery. Virtually all of the classes of effect sizes for the differ-ent mnemonics were homogeneous, suggesting that, withingroups, the different studies can be considered to be replica-tions of each other. Note, however, that some of the averageeffect sizes were not reliably different from zero, probably be-cause of small sample size.
Comparison of the effectiveness of different types of pre-
248 R VERHAEGHEN, A. MARCOEN, AND L. GOOSSENS
Table 5Regression of Selected Moderator Variables on Effect Size in Memory-Training Groups
R2 with otherPredictor B 0 p predictors
Full model (QE = 27.46, df= 35)
AgePre-to-posttest intervalTraining-to-posttest intervalNo. of sessionsDuration of sessionsSingle vs. multiple mnemonicsPretrainingMemory-related interventionsReal-life tutor vs. manual/tapeGroup sessionsPublication statusInclusion of control groupRecruitment for memory training
Constant
-0.0600-0.0048-0.0300-0.0025-0.4700-0.0395
0.36430.6609
-0.32070.60920.1482
-0.1760-0.1126
5.0041
-0.5922-0.2570-0.1609-0.0286-0.5920-0.0529
0.48470.7630
-0.27600.47290.1458
-0.1799-0.1483
.000
.280
.373
.928
.000
.787
.004
.007
.412
.012
.447
.250
.424
.000
.42
.78
.62
.87
.55
.66
.55
.84
.89
.64
.65
.48
.63
Restricted model (QE = 36.80, df= 43)
AgeDuration of sessionsPretrainingMemory-related interventionsGroup sessions
Constant
-0.0530-0.4522
0.31870.11060.61644.4476
-0.5236-0.5696
0.42410.12770.4785
.000
.000
.002
.373
.001
.000
.08
.41
.30
.39
.36
Note. QE = statistic for error sum of squares.
training was restricted to those studies that used the same typeof mnemonic: the name-face technique. Recall from theMethod section that two groups that received an interventionbefore training (viz., an attitude-improvement program) wereconsidered to be some kind of reference group and did notreceive pretraining in the proper sense of the term. The meta-analysis involved two different steps: (a) The weighted meanimprovement for all groups receiving pretraining was com-pared with the effect of attitude improvement both followingpretraining and following mnemonic training and (b) the effec-
Table 6Effect Sizes as a Function of Type of Mnemonic Taught
95% confidencelimits for d+
Mnemonic d+ Lower Upper
Method of lociName-facePegwordImagery (paired associates)Organization
Total (single)
1214212
31
0.800.830.620.140.850.81
0.580.69
-0.00-0.84
0.380.70
1.020.971.241.121.320.92
12.7823.16*0.01
—0.8539.05
Note. Dashes indicate that homogeneity cannot be computed be-cause there is only one study in the group. For total single mnemonic,QB= 2.25, ns. k= number of effect sizes; d, = mean weighted effect size;(?w = chi-square statistic for homogeneity within groups; Qe = chi-square statistic for homogeneity between groups.* Significant nonhomogeneity at p < .05.
tiveness of different types of pretraining was compared, againafter completion of the pretraining and of the training phase.Table 7 presents the results of that analysis.
The between-groups difference was nonsignificant immedi-ately after pretraining (QB = 1.51, ns), but reached significance((2B
= 8.25, p < .05) after completion of the subsequent mne-monic training. These findings suggest that, as far as the train-ing phase is concerned, it was indeed useful to distinguish be-tween pretraining and attitude improvement. The (?w statisticfor the pretraining groups was nonsignificant, indicating thatadditional partitionings, as a function of type of pretraining,for instance, were not called for. The lower part of Table 6(again provided for illustrative purposes) shows that all types ofpretraining were equally effective. All of the effect sizes for thedifferent types of pretraining were homogeneous. Althoughsome of the average effect sizes were not significant after pre-training, they all differed from zero after subsequent memorytraining.
Discussion
From our results, it is obvious that even in old age memoryremains plastic. The mere fact of retesting the elderly enhancestheir memory performance, with about 0.4 standard deviation.Training the elderly to use mnemonics enhances performance,with about 0.7 standard deviation. This implies that after mne-monic training, the average elderly person can be expected toperform at the 77th percentile of the performance distributionof his or her age group. Because the effect size for groups receiv-
IMPROVING MEMORY IN THE AGED 249
Table 7Relative Effectiveness of Pretraining as Compared With Attitude Improvement Groups andEffect Size as a Function of Type of Pretraining (Name-Face Mnemonic Only)
After pretraining
Class L/U <2w
After mnemonic training
L/U Q
Relative effectiveness
PretrainingAttitude-improvement
72
0.330.05
0.15/0.51-0.37/0.47
1.790.01
0.860.19
0.67/1.05-0.23/0.60
3.630.00
Type of pretraining
ImageryJudgmentImagery and judgmentRelaxation
2113
0.340.490.430.24
0.03/0.65-0.14/1.12
0.03/0.83-0.06/0.53
0.00
——0.91
0.921.140.750.71
0.59/1.240.47/1.800.35/1.160.25/1.17
1.62
——0.54
Note. Dashes indicate that homogeneity cannot be computed because there is only one study in thegroup. Within-group homogeneity statistics (Qw) are all nonsignificant at p < .05. k = number of effectsizes; d,. = mean weighted effect size; L/U = lower/upper bound of the 95% confidence interval for d+; Qw= chi-square statistic for homogeneity within groups.
ing mnemonic training was reliably larger than that for controland placebo conditions, part of this increase in performancemust be attributed to mnemonic treatment, over and abovemere retesting and placebo effects.
The plasticity associated with mnemonic training appears tobe largely specific to that training. Improvement was found tobe higher on tasks allowing for the use of the newly acquiredmnemonic than on tasks not allowing for the use of that mne-monic.
At least four variables were found to influence performancegains in the mnemonic-training groups. Treatment gains werelargest when the subjects were younger, when pretraining wasprovided, when training was carried out in groups, and whensessions were relatively short. Possibly, including some kind ofmemory-related intervention (such as attention training, pro-viding information about memory and aging, group discus-sion, and the like) also enhances treatment gain. When inter-preting these results, the reader should bear in mind that theresults of any regression analysis are strongly dependent on therange of the variables included in the regression model. Forinstance, the duration of training sessions in the present samplevaries from 20 min to 2.5 hr, with a median of 90 min. Theregression equation may hold within that range of variation,but it is in no way guaranteed (and in fact highly improbable)that further decreasing session duration will lead to larger gainsfrom treatment. Also, the reader should be aware that meta-analysis is merely a descriptive tool, and further research isnecessary to explain the influence of the variables mentionedearlier.
One finding that certainly merits further investigation is thefact that age, within older samples, negatively affected treat-ment gain. This echoes findings that there are differences inplasticity between young and older adults (e.g., Kliegl et al.,1989). This seems to indicate that—at least in cross-sectionalsamples—memory plasticity decreases monotonically over theadult life span. Several reasons, which are not necessarily mutu-ally exclusive, could be advanced for this finding. A lack of
performance gain after instruction in an effective mnemoniccan occur in at least three instances: (a) There might be prob-lems with the acquisition of the mnemonic; (b) there might beproblems with retrieval of the mnemonic at posttest (if forget-ting of episodic information is age related, forgetting of proce-dural information might be age-related as well); and (c) theremight be problems with the application of the mnemonic.
All of these problems can be explained from a processing-limitation view on memory aging. A corollary of a reduction inprocessing resources is that there should be problems with theacquisition and retrieval of information. Application problemscan be explained by the possibility, put forward by some au-thors (e.g., Backman, 1989; G. Cohen, 1988; Salthouse, 1985; fora thorough review, see Light, 1991), that age limitations in pro-cessing resources (such as speed of processing and working-memory capacity) might lead to concomitant changes in strat-egy use. The age-related reduction in resources should lead tothe adoption of less effortful strategies and should set limits onthe kind of strategies that can be used (or the number or se-quence of operations that can be carried out). However, as Light(1991) pointed out, empirical data to support this assertion arelacking.
Of course, it is possible that more distal factors, such as educa-tional and health differences, differences in cognitive stimula-tion in the living environment, or differences in previous partic-ipation in adult education activities, are responsible for prob-lems in acquisition, retrieval, or application of mnemonics.Note that in the present meta-analysis, however, educationaldifferences were not associated with treatment gain.
Some of the points raised here can be clarified through train-ing research in which (a) it is verified whether subjects haveindeed learned the mnemonic correctly after completion of thetraining phase, (b) the mnemonics applied by the subjects atpre- and posttest occasions are identified, and (c) some relevantindividual measures (e.g., of educational level, general health,and processing resources) are included (at least) at pretest. Thisimplies a shift from a group approach of memory-training data
250 P. VERHAEGHEN, A. MARCOEN, AND L. GOOSSENS
analysis to an individual-differences approach (as advocated byWillis, 1990).
The finding that longer sessions (note that the median dura-tion of sessions is 1.5 hr) have less effect can be attributed to theeffects of fatigue. It is conceivable that long training sessions aretiring and that this may lead to problems with the acquisition ofthe mnemonic or to a decrease in motivation.
The positive effects of group instruction (and memory-re-lated interventions) should be investigated further. Some likelycandidates for an explanation are social comparison and a re-sulting feeling of self-efficacy, reactivation, mutual support andreinforcement among the trainees, or enhanced motivation.
With regard to the effects of pretraining, a methodologicalproblem arises. In our sample, the presence of pretraining ismethodologically confounded with number of testing occa-sions: Pretraining studies include three testing occasions, asopposed to two for non-pretraining studies. It may be possiblethat the larger pre-to-posttest gain is simply attributable to thelarger retest effect that might be expected after two previoustesting occasions. A second possibility is that the effect of pre-training is comparable with that of other memory-related inter-ventions. To check this possibility, it is necessary to comparepretraining training groups with groups receiving the pretrain-ing mixed with the training. (An examination of order effects—pretraining training vs. training pretraining—is problematicbecause the training-to-posttest interval is different for the twogroups.) At present, the finding that groups receiving placebotreatment (an attitude-improvement program) before trainingperformed less well after training than the pretraining traininggroups pleads against this hypothesis. However, as stated ear-lier, the treatment gain in the former groups was rather low. Athird possibility—after ruling out both of the former possibili-ties—is that pretraining has indeed a specific effect. In thatcase, it should also be expected that subjects who do less well onpretest measures of the variable relevant to the pretraining (i.e.,subjects scoring low on imagery, low on judgment, and high onanxiety, respectively) should benefit more from the relevant pre-training (i.e., imagery, judgment, and relaxation training, re-spectively) than other subjects. Yesavage (1984) and Yesavage,Sheikh, Tanke, and Hill (1988) found indeed that higher anxi-ety scores were associated with larger treatment gain in a relax-ation pretraining design, and Yesavage et al. (1988) also foundthat lower vocabulary scores were associated with larger treat-ment gains in a judgment pretraining. Note that this argumentis internal to pretraining designs; no conclusions are permittedfrom these findings regarding the superiority of pretrainingover other memory-related interventions.
It may be interesting to point out that the influence of someother variables did not reach significance, although regressioncoefficients are usually in the expected directions. These vari-ables include pre-to-posttest and training-to-posttest interval,real-life tutoring versus manual/tape, and publication status.Note that instruction in a package of mnemonic techniquesrather than training a single mnemonic does not lead to anincrease in effect size.
It is important to note that the approach taken here has itslimitations. First, these results bear strictly on mnemonic train-ing for the normal elderly and must not be generalized to otherpopulations, such as the elderly suffering from dementia. Sec-
ond, these results pertain to memory performance on classicalepisodic memory tasks. Nothing can be inferred about the im-pact of mnemonic training on everyday memory performanceor on metamemory.
No differences were found in effects of memory training as afunction of type of mnemonic treatment or type of pretraining.Almost all of the mnemonic treatments, however, involved im-agery. Only two studies investigated a purely verbal mnemonic(viz., organization). The treatment gain associated with this ver-bal mnemonic was apparently not larger than that for the visualmnemonics (contrary to what is sometimes assumed; see Yesa-vage et al, 1989).
We summarize, then, by stating that mnemonic training inthe elderly enhances performance reliably more than eithermere retesting or placebo treatment. Variables that influenceperformance gains negatively are age of the subjects and sessionduration. Group training and pretraining (and possibly mem-ory-related interventions) influenced performance gain posi-tively. No differences could be found in the effectiveness ofdifferent kinds of mnemonic techniques or different types ofpretraining. In all, memory appears to be potentially plastic,even in old age.
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Received January 2,1991Revision received October 8,1991
Accepted October 8,1991 •
