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Everyday Memory and Working Memory in Adolescents With Mild Intellectual Disability M. J. Van der Molen Utrecht University (Amsterdam, The Netherlands) J. E. H. Van Luit Utrecht University (Utrecht, The Netherlands) Maurits W. Van der Molen University of Amsterdam (Amsterdam, The Netherlands) Marian J. Jongmans Wilhelmina Children’s Hospital (Utrecht, The Netherlands) Abstract Everyday memory and its relationship to working memory was investigated in adolescents with mild intellectual disability and compared to typically developing adolescents of the same age (CA) and younger children matched on mental age (MA). Results showed a delay on almost all memory measures for the adolescents with mild intellectual disability compared to the CA control adolescents. Compared to the MA control children, the adolescents with mild intellectual disability performed less well on a general everyday memory index. Only some significant associations were found between everyday memory and working memory for the mild intellectual disability group. These findings were interpreted to suggest that adolescents with mild intellectual disability have difficulty in making optimal use of their working memory when new or complex situations tax their abilities. DOI: 10.1352/1944-7558-115.3.207 In this study we focused on memory tasks in everyday life and their relationship to working memory in adolescents with mild intellectual disability. Many activities encountered daily depend on remembering things for short periods of time, at least long enough to be able to write it down (e.g., a telephone number or the spelling of a novel name) (Gathercole, 1999). In addition to short-term memory demands, individuals need active maintenance and processing of informa- tion, in essence, working memory processes (Baddeley, 1986; Engle, Kane, & Tuholski, 1999), for example, when one has to step out of a routine activity, such as driving to the dentist, instead of the usual trip to work (Unsworth & Engle, 2007). Everyday memory activities are necessary for leading an independent life (Kazui et al., 2005). Adults and children for whom an age-appropriate autonomous life is not self-evident have been involved in studies on everyday memory. Target groups include adults suffering from Alzheimer (e.g., Clare et al., 2000), children with epilepsy (e.g., Kadis, Stollstorff, Elliott, Lach, & Smith, 2004), and children born prematurely (e.g., Briscoe, Gathercole, & Marlow, 2001). Studies have also been conducted on everyday memory with adults who have intellectual disability (e.g., Numminen, Service, Ahonen, & Ruoppila, 2001). Researchers conducting studies of everyday memory usually employ laboratory tests imitating everyday memory situations. The Rivermead VOLUME 115, NUMBER 3: 207–217 | MAY 2010 AJIDD E American Association on Intellectual and Developmental Disabilities 207

Everyday Memory and Working Memory in Adolescents With Mild Intellectual Disability

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Everyday Memory and Working Memory inAdolescents With Mild Intellectual Disability

M. J. Van der MolenUtrecht University (Amsterdam, The Netherlands)

J. E. H. Van LuitUtrecht University (Utrecht, The Netherlands)

Maurits W. Van der MolenUniversity of Amsterdam (Amsterdam, The Netherlands)

Marian J. JongmansWilhelmina Children’s Hospital (Utrecht, The Netherlands)

AbstractEveryday memory and its relationship to working memory was investigated in adolescentswith mild intellectual disability and compared to typically developing adolescents of thesame age (CA) and younger children matched on mental age (MA). Results showed a delay onalmost all memory measures for the adolescents with mild intellectual disability compared tothe CA control adolescents. Compared to the MA control children, the adolescents withmild intellectual disability performed less well on a general everyday memory index. Onlysome significant associations were found between everyday memory and working memory forthe mild intellectual disability group. These findings were interpreted to suggest thatadolescents with mild intellectual disability have difficulty in making optimal use of theirworking memory when new or complex situations tax their abilities.

DOI: 10.1352/1944-7558-115.3.207

In this study we focused on memory tasks ineveryday life and their relationship to workingmemory in adolescents with mild intellectualdisability. Many activities encountered dailydepend on remembering things for short periodsof time, at least long enough to be able to write itdown (e.g., a telephone number or the spelling ofa novel name) (Gathercole, 1999). In addition toshort-term memory demands, individuals needactive maintenance and processing of informa-tion, in essence, working memory processes(Baddeley, 1986; Engle, Kane, & Tuholski,1999), for example, when one has to step out ofa routine activity, such as driving to the dentist,instead of the usual trip to work (Unsworth &Engle, 2007).

Everyday memory activities are necessary forleading an independent life (Kazui et al., 2005).Adults and children for whom an age-appropriateautonomous life is not self-evident have beeninvolved in studies on everyday memory. Targetgroups include adults suffering from Alzheimer(e.g., Clare et al., 2000), children with epilepsy(e.g., Kadis, Stollstorff, Elliott, Lach, & Smith,2004), and children born prematurely (e.g.,Briscoe, Gathercole, & Marlow, 2001). Studieshave also been conducted on everyday memorywith adults who have intellectual disability (e.g.,Numminen, Service, Ahonen, & Ruoppila, 2001).

Researchers conducting studies of everydaymemory usually employ laboratory tests imitatingeveryday memory situations. The Rivermead

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E American Association on Intellectual and Developmental Disabilities 207

Behavioural Memory Test–hereafter referred to asthe Behavioural Memory Test (Wilson, Cock-burn, & Baddeley, 1985) is probably the bestknown and most frequently used. It consists of 11verbal, spatial, and visual subtests, such asremembering a short story or directions andrecognizing a picture. Another means of assessingeveryday memory is asking the individual, orimportant people around that individual, howeasy or difficult it is to remember things ineveryday life (e.g., Kadis et al., 2004).

Understanding weak everyday memory func-tioning in adults and children with mild intellec-tual disability is crucial to improve support at anindividual level. Such support might enhancetheir ability to live as autonomously as possible,thereby resulting in a higher perceived quality oflife and fewer demands on society (Lachapelle etal., 2005). However, to our knowledge, only twostudies have been conducted to examine everyday memory in people with mild intellectualdisability. Numminen et al. (2001) comparedadults with Down syndrome (mean age 42 years)to adults with disability of unknown etiology(mean age 51 years), matched on nonverbalintelligence (IQ range 5 35 to 70) on theBehavioural Memory Test. Both groups per-formed similarly on two of the indices in thismeasure: Total score and Story Recall score.Martin, West, Cull, and Adams (2000) assessedBehavioural Memory Test performances of agroup of adults with mild intellectual disability(mean age 32 years, IQ range 5 55 to 75) andobserved that although these adults have parti-cular difficulty with remembering a story, recog-nition of visual information is relatively easy forthem.

We could not find any studies on the topic ofeveryday memory functioning in adolescents withmild intellectual disability. This is unfortunatebecause knowledge about their daily memoryfunctioning could be useful in determining whichtypes of support or training would assist theseadolescents inside and outside the classroom. Inaddition, such knowledge might provide guide-lines on how to compensate for possible short-comings early in life.

Although everyday memory strengths andweaknesses in adolescents with mild intellectualdisability are unknown, researchers have focusedon short-term memory and working memory ofthese adolescents. Results of these studies indicatethat children and adolescents with mild intellec-

tual disability perform poorly on most tests thatmeasure verbal short-term memory and workingmemory, but they perform averagely on visualshort-term memory (Henry, 2001; Van derMolen, Van Luit, Jongmans, & Van der Molen,2007; Van der Molen, Van Luit, Jongmans, & Vander Molen, 2009). Short-term memory is defined asthe capacity to retain information for brief periodsof time (Gathercole, 1999). Kimberg and Farah(1993) defined working memory as comprising setsof perceptual, mnemonic, and action representa-tions that are currently active in order to fulfill atask. Performance in working memory tasks isthen determined by the levels of activation ofrelevant representations and the ability to ade-quately discriminate between relevant and irrele-vant representations (Kimberg, D’Esposito, &Farah, 1997). These researchers found, for exam-ple, that patients with prefront brain damage showdifficulties in performing everyday tasks becausethe associations among those working memoryrepresentations are weak (Kimberg & Farah, 1993).When tasks are routine and automatic, however,and the environment is highly structured, therebylimiting the range of possible responses, and whenit is clear which response is most relevant, thesepatients are expected to perform well on everydaytasks (Kimberg et al., 1997).

Based on the research discussed above, in thepresent study we predicted that relations existbetween everyday memory and working memorywhen memory tasks are demanding. Furthermore,these relations will not exist when memory tasksare routine. Our principal aim in the current studywas to assess everyday memory functioning inadolescents with mild intellectual disability. Inorder to contrast their performance to that ofchildren and adolescents who are developingtypically, we compared their scores to adolescentsmatched on chronological age (CA) and mentalage (MA). We predicted that the adolescents withmild intellectual disability, having a weak workingmemory, will perform less well on complexeveryday memory tasks that necessitate demand-ing multiple relevant representations, but fairlywell on simple, structured, or automatic everydaymemory tasks. Our second aim was to investigatethe associations between everyday memory andworking memory in adolescents with mild in-tellectual disability compared with CA- and MA-matched control groups. We hypothesized thatthere would be associations between complexeveryday memory tasks and working memory

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Memory in adolescents with mild intellectual disability M. J. Van der Molen et al.

208 E American Association on Intellectual and Developmental Disabilities

tasks, but not between simple everyday memorytasks and working memory tasks.

Method

ParticipantsA total of 104 children and adolescents

participated in the study, including 39 adolescentswith mild intellectual disability (21 boys, 18 girls)ranging in age from 13 to 17 years. Theseadolescents attended special schools for pupilswith mild intellectual disability. Their IQ rangewas between 55 and 75, which is the standardrange accepted by the American Association onIntellectual and Developmental Disability, for-merly the American Association on MentalRetardation (Luckasson et al., 2002), for childrenand adolescents with mild intellectual disability.Adolescents diagnosed by psychiatrists as havingattention deficit hyperactivity disorder, pervasivedevelopmental disorder-not otherwise specified,or other specific etiologies were excluded becausethese psychiatric problems are associated withspecific working memory strengths and weaknesses(Gathercole & Alloway, 2006), which mightinfluence the results.

We recruited two control groups, onematched on CA and the other on MA, whichwas calculated by (Full Scale IQ 3 age)/100. Wealso compared total mean raw scores of the Dutchversion of the Wechsler Intelligence Scale forChildren—WISC-III (Kort et al., 2005) for bothgroups. The CA group consisted of 39 typicallydeveloping adolescents (17 boys, 22 girls) whoranged in age from 13 to 16 years. We recruitedthis group from three regular secondary schools.The MA group was composed of 26 typicallydeveloping children (10 boys, 16 girls) who rangedin age from 9 to 12 years. We recruited them fromtwo regular primary schools. Informed consentwas obtained for every participant.

All participants had normal or corrected visionand were reported to be healthy as noted in their

school records. Ethnicity and social economicalstatus were comparable in all three groups.Additional descriptive details are provided inTable 1. To obtain information on IQ and MAof children and adolescents, we administered thefull Dutch version of the WISC-III. Comparisonsindicated that the group with mild intellectualdisability did not differ in CA from the CA-matched group, t(1, 86) 5 .74, p 5 .46. The mildintellectual disability group did not differ in MAfrom the MA-matched group, t(1,59) 5 .90, p 5

.37, although the p value did not reach the .50 levelas recommended by Mervis and Klein-Tasman(2004), the difference in absolute terms was lessthan 3 months. The mild intellectual disability andthe MA group did not differ on the total raw scoreof the WISC-III, t(1, 59) 5 1.31, p 5 .20. Althoughthe p-value did not reach the .50 level, the absolutedifference in total raw score was only 10 points(mild intellectual disability 5 257; MA group 5

267). Analyses revealed that there were no genderdifferences in the complete group of children andadolescents, F(2, 90) 5 1.36, p 5 .17. Therefore,gender is not considered further.

ProcedureWe tested all children and adolescents in a

quiet room at their school. The WISC-III wasadministered during one session of about 75 minand the memory tasks, during a second session ofabout 60 min, both within one day, with at least a1.5-hour interval.

MeasuresWe employed one test and two question-

naires to assess memory functioning in everydaylife and seven tests to assess short-term memoryand working memory.

We administrated the Behavioural MemoryTest (Wilson et al., 1985; Dutch version by VanBalen & Groot Zwaaftink, 1987) to assess memoryproblems in everyday life. This test, which

Table 1. Participant Characteristics by Group

Characteristica

Mild intellectual disability (n 5 39) CA-matched (n 5 39) MA-matched (n 5 26)

Mean SD Mean SD Mean SD

FSIQ 65.0 5.29 99.8 7.60 97.1 7.86

CAb 181.5 11.95 183.0 5.74 124.4 10.78

MAb 118.1 11.12 182.6 13.80 120.7 12.23aFSIQ 5 Full Scale IQ. bIn months.

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contains analogies for everyday situations inwhich memory is used, has been employed withindividuals who have mild intellectual disability(Martin et al., 2000). The test contains 11 verbal,visual, and spatial subtests. For this study we usedthe Behavioural Memory Test screen componentand present the standardized total score, which isthe sum of the standardized scores of the 11individual subtests; therefore, it can be regarded asa general index of memory in everyday life.

In order to obtain more detailed informationand to allow comparisons to scores on theworking memory tasks, we used an additional 3raw subscores. Story Recall is a subtest in which astory has to be repeated immediately afterpresentation and 20 minutes later. The VisualRecognition subtest illustrations and photos offaces also have to be recognized. Finally, theRoute Recall subtest requires the child to walk ashort route shown and verbally supported by theexperimenter. The child has to pick up anenvelope along the route and later put it downon a specific spot. The route task immediatelyfollows the initial example provided by theexperimenter after a delay of about 15 min.

We consider the Behavioural Memory TestVisual Recognition to be a simple everydaymemory task because it is highly structured andthe information only has to be recognized. Boththe Story Recall and Route Recall subtestsrepresent complex everyday memory tasks. Inboth tasks more information has to be remem-bered, and in the case of Route Recall, multiplerelevant representations have to be kept in mind.

We did not individually analyze the remain-ing subtest scores because they were inappropriatefor the current goal. That is, they contained onlyone item (i.e., remembering a name) or wereorientation-based (e.g., What day is it?). In sum,four subtests of the Behavioural Memory Testscores were used in the current study: Screening,Story Recall, Visual Recognition, and RouteRecall.

The Everyday Memory Questionnaire forChildren, Child Version (Van Leeuwen, 1990)consists of nine questions about the child’smemory functioning in everyday life, such asremembering what has been read or what has beendone that day. Each question consists of two stagesthat are recommended for people with intellectualdisability (Finlay & Lyons, 2001). The child firstdecides whether he or she belongs with childrenwho can remember something well (e.g., a song or a

shopping list) or with children who do notremember things well. Then the child decideswhether he or she belongs with the chosen groupvery much or only a bit. Three points are given ifthe child responds that he or she belongs very muchto the group who does not remember well; if he orshe belongs with that group just a bit; 2 points aregiven. When the child belongs a bit to the groupwho can remember things well, 1 point is given; forbelonging very much to that group, no points aregiven. A higher score indicates that the child didnot report memory accurately.

The Everyday Memory Questionnaire forChildren, Parent Version (Van Leeuwen, 1993)contains 24 items questioning parents about theirchild’s memory (e.g., do you think your child isable to remember a song or a telephone number?)Each answer is scored from 0 to 4. The higher thescore, the more memory problems the child has.The mild intellectual disability group did notdiffer in MA from the MA-matched group, t(1,59)5 .90, p 5 .37.

Working Memory TestsDigit recall and nonword recall (Baddeley,

1986) both measure verbal short-term memory,which is an aspect of working memory. In thesetests digits and Dutch sounding nonwords (e.g.,lut, pog) have to be repeated in the same order asthey were presented. Both tests start withsequences of two items (digits or nonwords) upto sequences of six items. In both tests there arethree trials for each sequence, but when two trialsare correctly repeated, the third is omitted but onepoint is awarded. To assess visual short-termmemory, we administered two tests. Block Recallis identical to the Corsi test, but in this study weused the instructions from Pickering and Gath-ercole (2001). The experimenter taps a sequenceof 3-dimensional blocks that the child has torepeat in the same order. The task starts with oneblock and increases to sequences of nine blocks.There are six trials for each sequence. In theVisual Patterns test (Della Sala, Gray, Baddeley, &Wilson, 1997), the child is shown a matrixdepicted on a stimulus card, varying in config-uration from 2 3 2 to 5 3 6 squares; half of thesquares are white and the other half, black. Afterinspecting a stimulus card for 3 s, the child has toindicate the black squares in the blank grid on theresponse sheet. Three stimulus cards are providedfor each of the 14 difficulty levels.

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Memory in adolescents with mild intellectual disability M. J. Van der Molen et al.

210 E American Association on Intellectual and Developmental Disabilities

We administered two verbal working memorytests. In Backward Digit Recall (Pickering &Gathercole, 2001), the child has to repeat spokenlists of digits, but in the reverse order. Procedureand scoring for this task is similar to that for DigitRecall. Listening Recall (Pickering & Gathercole,2001, which was translated into Dutch and adaptedso as to make the syllabic length of the to-be-remembered words comparable to the Englishversion, requires the child to listen to simplestatements and determine whether they are true orfalse, while at the same time remembering the lastword of each statement. Following each trial, theselast words had to be repeated in the same order aspresented. Listening Recall starts with one sentenceand increases to a maximum of six. Six trials areavailable for each sequence, and the next sequenceis presented after four correct trials. One point isgive for each omitted trial. The Odd-One-Out test(Henry, 2001) measures visual working memory.Because Henry reported a possible ceiling effect,we extended the test with an extra item afterconsultation with the author (L. A. Henry, personalcommunication, April 27, 2005). Each trial con-tains a sequence of three figures, two of which aresimilar and one is slightly different, that is, the odd-one-out. The child has to decide which figure is theodd-one-out and remember its location. Followingeach trial, the child has to point to the locations ofthe odd-one-outs in the same sequence as pre-sented. Trials start with two sequences, going to amaximum of six. Three trials are given for eachsequence length.

Data AnalysisFirst, we conducted a multivariate analysis

of variance (MANOVA) on scores from theBehavioural Memory Test, the Everyday MemoryQuestionnaire-Child Version, and the Short-Term Memory and Working Memory tests.Because data for 17 children and adolescentswere missing on the Everyday Memory Ques-tionnaire-Parent Version, we analyzed thistest separately, using a univariate analysis ofvariance (ANOVA). We utilized the Scheffeprocedure for post-hoc analyses when test var-iances were similar and Tamhane’s procedurewhen test variances differed. Our next step wasto examine correlations between the BehaviouralMemory Test and the two administered memoryquestionnaires versus the 9 working memoryscores, using bivariate correlation analysis. To

reduce the number of short-term memory andworking memory variables, we calculated com-pound scores by linearly transforming scoresto similar scales. This resulted in one verbalshort-term memory index (a compound scoreof Digit Recall and Nonword Recall), a visualshort-term memory index (a compound scoreof Block Recall and the Visual Patterns test),and a working memory index (a compoundscore of Backward Digit Recall, ListeningRecall, and the Odd-One-Out test). Finally,stepwise linear regression analyses were carriedout for each of the three groups to investigatewhether the three short-term memory and work-ing memory indices were related to everydaymemory as indexed by the Behavioural MemoryTest Screening score and the three selected subtestscores: Story Recall, Visual Recognition, andRoute Recall.

Results

Table 2 shows mean scores, SDs, groupeffects, and effect sizes of all administered testsand questionnaires.

Everyday Memory PerformanceMANOVAs revealed significant group effects

for all Behavioural Memory Test scores except thesubtest Visual Recognition. On this subtest allthree groups showed a ceiling effect. Almost allchildren and adolescents obtained the highestscore possible. Scores for both control groups, butnot the mild intellectual disability group, alsoshowed a ceiling effect on Route Recall. Post-hocanalyses revealed that the mild intellectualdisability group performed less well than the CAgroup on the subtests Screening, Story Recall, andRoute Recall, all ps , .01, whereas both groupsscored equally well on Visual Recognition.Compared to the MA group, adolescents in themild intellectual disability group scored signifi-cantly lower on Screening and Route Recall, ps ,

.01. However, because the score of the subtestRoute Recall contributed to the score on Screen-ing, we repeated the analysis with Route Recall asa covariate. The results confirmed a significantlylower score on Screening for the mild intellectualdisability group compared to both the CA andMA control groups, p , .01. In addition, the MAgroup performed less well than did the CAcontrol group on Screening, p , .01, and Story

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Memory in adolescents with mild intellectual disability M. J. Van der Molen et al.

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Tab

le2.

Per

form

ance

by

Gro

up

on

the

Mem

ory

Tas

ks

Task

a

Mild

IDb

(n5

39)

CA

-matc

hed

(n5

39)

MA

-matc

hed

(n5

26)

Fd

cC

A/M

Ad

Mean

SDM

ean

SDM

ean

SD

Eve

ryd

ay

mem

ory

RB

MT

e

Scre

en

ing

(12)

8.5

11.9

410.9

5.9

49.7

71.4

525.3

81.6

0**/.36*

*

Sto

ry(4

2)

9.3

25.0

116.7

45.1

610.7

74.8

423.2

31.3

0**/.29

Vis

ual

reco

gn

itio

n(1

5)

14.9

0.3

814.9

5.2

214.8

5.5

4.5

7.1

6/.10

Ro

ute

Reca

ll(1

0)

8.8

71.5

29.9

5.2

29.9

2.2

715.2

1.9

9**/.96**

Eve

ryd

ay

Mem

ory

Qu

est

ion

nair

e-C

hild

(27)

10.9

74.7

010.3

37.3

57.7

73.3

82.7

4.1

0/.78

Eve

ryd

ay

Mem

ory

Qu

est

ion

nair

e-P

are

nt

(96)

32.3

016.1

115.7

111.1

118.8

511.8

413.2

91.1

9**/.95*

*

Sho

rt-t

erm

mem

ory

an

dw

ork

ing

mem

ory

Dig

itR

eca

ll(1

8)

10.4

92.3

414.2

62.2

010.9

21.9

632.9

71.6

6**/.20

No

nw

ord

Reca

ll(1

8)

5.1

31.9

87.2

12.0

06.4

61.7

911.3

71.0

4**/.70*

*

Blo

ckR

eca

ll(5

4)

25.4

13.1

030.3

14.3

127.4

22.4

819.4

21.3

0**/.72*

*

Vis

ual

Patt

ern

s(4

2)

15.2

83.3

020.2

63.8

814.6

93.8

724.7

61.3

8**/.08

Back

ward

Dig

itR

eca

ll(1

8)

5.7

41.9

78.6

22.6

76.8

81.9

925.9

31.2

3**/.57

List

en

ing

Reca

ll(3

6)

12.4

13.5

916.2

32.9

214.5

02.4

015.0

21.1

7**/.68*

*

Od

d-O

ne-O

ut

(15)

7.7

43.0

811.2

62.6

48.4

24.0

312.8

91.2

3**/.19

aN

um

ber

sin

par

enth

eses

are

max

imu

msc

ore

sp

erte

st.b

Inte

llec

tual

dis

abilit

y.cC

oh

en’s

d5

effe

ctsi

ze(.

1to

.3:

smal

l,.3

to.5

:m

od

erat

e,.5

to1.

0:la

rge,

ove

r1.

0:ve

ryla

rge.

dC

hro

no

logi

cal

age/

men

tal

age.

eR

iver

mea

dB

ehav

iou

ral

Mem

ory

Tes

t.**

p,

.01.

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Memory in adolescents with mild intellectual disability M. J. Van der Molen et al.

212 E American Association on Intellectual and Developmental Disabilities

Recall, p , .01, but equally well on VisualRecognition and Route Recall.

In line with our first prediction, the adoles-cents with mild intellectual disability had anaverage performance on the Behavioural MemoryTest subtest Visual Recognition, which we con-sidered to be a simple everyday memory task, butless well on Story Recall, and even worse on RouteRecall, both of which we believe are complexeveryday memory tasks.

Contrary to the Everyday Memory Question-naire-Child Version, for which no significantgroup effect was found, we observed a significantgroup effect (ANOVA) for the Everyday MemoryQuestionnaire-Parent Version. Post-hoc analysesrevealed that parents of the adolescents with mildintellectual disability perceived their child’s every-day memory to be poor, indicated by a higherscore, than did parents of the CA-matchedadolescents and the MA-matched children, ps ,

.01.

Short-Term and Working Memory PerformanceMANOVAs revealed significant group effects

on Digit Recall and Nonword Recall. Post-hocanalysis indicated that for Digit Recall, the mildintellectual disability and MA groups performedequally, but both groups did less well than did theCA group, ps , .00. The post-hoc analysis forNonword Recall showed that the mild intellectualdisability group performed less well than did theMA and CA groups, ps , .05 and .00, respec-tively.

For both Block Recall and the Visual Patternstests, MANOVAs revealed significant groupeffects. Post-hoc analyses indicated that on BlockRecall, the mild intellectual disability groupperformed less well than did the MA and theCA groups, ps , .05 and .00, respectively). On theVisual Patterns test, however, the mild intellectualdisability group performed equally well as the MAgroup did, but less well than the CA group, p ,

.001.MANOVAs revealed that the mild intellec-

tual disability group performed more poorly onListening Recall than did the MA and CA groups,ps , .05 and .001, respectively. On BackwardDigit Recall, the mild intellectual disability andMA group did not differ. However, the mildintellectual disability group performed morepoorly than the CA group, p , .001. To be surethat the differences on both verbal working

memory tasks were not influenced by a verbalshort-term memory delay, we performed a MAN-COVA with Nonword Recall as covariate. Theanalysis showed that despite this correction, theeffects remained. Analysis of the Odd-One-Outtest scores showed significant group effects. Themild intellectual disability group performedsimilarly to the MA group, but less well on thistest than did the CA group, p , .01. Whencorrecting for Block Recall (MANCOVA), wefound that the effect remained.

In sum, on all short-term and workingmemory tests, the adolescents with mild intellec-tual disability did less well than the CA-matchedcontrol adolescents. However, although theyperformed as well as the MA control childrenon four of these tests, they did less well onNonword Recall, Block Recall, and ListeningRecall.

Associations Between Everyday and WorkingMemory Performances

Table 3 shows the statistically significantcorrelation coefficients between the BehaviouralMemory Test indices versus the short-termmemory and working memory indices for eachgroups. For the mild intellectual disability group,we found significant correlations between Beha-vioural Memory Test Screening and verbal short-term memory, and between Behavioural MemoryTest Route Recall and visual short-term memory.The MA group showed significant correlationsbetween Screening and working memory andbetween Story Recall and working memory. Weobserved a significant correlation for the CAgroup between the Everyday Memory Question-naire-Child Version and the Everyday MemoryQuestionnaire-Parent Version.

Given the moderate correlations betweenshort-term memory and working memory indiceson the one side and Behavioural Memory Testindices on the other side for the mild intellectualdisability group and the MA control group, weconducted a series of stepwise multiple regressionanalyses for these two groups. The dependentvariable was Behavioural Memory Test Screeningand the independent variables were verbal short-term memory, visual short-term memory, andworking memory indices. In the mild intellectualdisability group, the verbal short-term memoryindex accounted for 11% of the variance inScreening, b 5 .37, F(1, 37) 5 5.84, p , .05; for

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the MA group, the working memory indexaccounted for 16% of the variance of the Screen-ing, b 5 .44, F(1, 24) 5 5.86, p , .05. The otherBehavioural Memory Test outcome measures(Story Recall, Visual Recognition, and RouteRecall) were analyzed in the same way as Screen-ing (stepwise with the three short-term memoryand working memory indices as independentvariables). This was exploratory because weacknowledge that performing many analysesmight lead to spurious findings. The visualshort-term memory index accounted for 18% ofthe variance in Route Recall only for theadolescents with mild intellectual disability, b 5

.43; F(1, 37) 5 8.19, p , .01.With regard to our second prediction, asso-

ciations (correlations and regression analyses)were found between scores of complex everydaymemory tasks and working memory within theMA group. However, this was not the case for theadolescents with mild intellectual disability. Theirscores on complex everyday memory tasks werenot significantly associated with working memory,rather, with short-term memory. There were noassociations observed between the BehaviouralMemory Test scores and short-term memory orworking memory scores for the CA controladolescents.

Discussion

Results of the present study show thatadolescents with mild intellectual disability per-form less well than do CA-matched controladolescents on three aspects of memory ineveryday life as measured with the BehaviouralMemory Test: Screening score, which is a totalscore, and the subtests Story Recall and RouteRecall. In contrast, on Behavioural Memory Test

Visual Recognition, both groups scored equallywell. Although this might not reflect a true nullresult, because all groups showed a ceiling effecton this subtest, it seems to be a rather strongaspect of the memory abilities of the adolescentswith mild intellectual disability. This visualrecognition strength is consistent with the resultsof Martin et al. (2000), who showed thatrecognizing visual information is relatively easyfor adults with mild intellectual disability. Incomparison with MA control children, theadolescents with mild intellectual disability per-formed equally well on recalling a story and onrecognizing pictures. In contrast, the adolescents’Behavioural Memory Test Screening and RouteRecall revealed differences. The screening scorewas lower for adolescents with mild intellectualdisability than for the MA control children, evenwhen corrected for Route Recall. These results arein line with our first prediction, namely, thatadolescents with mild intellectual disability wouldhave problems with complex everyday memorytasks, such as remembering a route demandingmultiple relevant representations, but not withsimple, more structured everyday memory tasks,such as recognizing pictures.

The apparent deficit in complex everydaymemory for adolescents with mild intellectualdisability was confirmed by their parents, whorated their child’s memory as poorer than did theparents of both the MA and CA controladolescents. It is interesting that the adolescentswith mild intellectual disability themselves judgedotherwise; they rated their own memory as beingas good as the MA and CA control participants.This finding is consistent with the results reportedpreviously by Elias (2005). She compared per-ceived cognitive competence by children withmild intellectual disability (aged 6 to 8 years) with

Table 3. Correlation Coefficients for Memory Indices by Group

Test Mild IDa CA-matched MA-matched

RBMTb

Screening–verbal short-term memory .37* 2.19 2.06

Screening–working memory .20 .14 .45*

Story Recall–working memory .13 .14 .39*

Route Recall–visual short-term memory .43** 2.25 .08

Everyday Memory Questionnaire-Parent Version–Everyday

Memory Questionnaire-Child Version .19 .52** 2.11aIntellectual disability. bRivermead Behavioural Memory Test.*p , .05. **p , .01.

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the judgment of their own teacher. These childrenwere less capable at accurately judging theircognitive competence, which they overestimated.Crabtree and Rutland (2001) obtained similarresults for adolescents with intellectual disability(mean age 14 years) who had to rate, among otherthings, their own scholastic functioning. Therewere no differences in their scholastic evaluationcompared to those of typically developing ado-lescents, even when the adolescents with intellec-tual disability were explicitly asked to comparethemselves with typically developing adolescents.Gilger (1992) also showed that the younger andthe less intellectually capable an individual, theless he or she is able to evaluate his or her owncompetencies. In the present study, however, theadolescents were not explicitly asked to comparetheir memory functioning to typically developingadolescents. Therefore, the adolescents may havecompared their own memory functioning withthe memory functioning of their classmates whohad intellectual disability.

The adolescents with mild intellectual dis-ability performed less well than did the CAcontrol group on all verbal and visual short-termmemory and working memory tests. Compared tothe MA control children, results were mixed; theadolescents with mild intellectual disability per-formed more poorly on Nonword Recall (verbalshort-term memory), Block Recall (visual short-term memory) and Listening Recall (verbal work-ing memory), but they performed equally well onthe other four tasks. Specific short-term memoryand working memory strengths and weaknesses,rather than an overall delay, have been reportedpreviously in populations with intellectual dis-ability (e.g., Henry & MacLean, 2002; Rosenquist,Conners, & Roskos-Ewoldsen, 2003; Van derMolen, van Luit, Van Der Molen, Klugkist, &Jongmans, 2010).

The relationship between everyday memoryand working memory was analyzed separately foreach of the three groups. We expected to findassociations between scores on complex everydaymemory tasks and working memory tasks. Instead,although having difficulties with complex every-day memory tasks such as recalling a route,performance on those tasks did not relate toperformance on working memory tasks but,rather, to scores on short-term memory tasks foradolescents with mild intellectual disability.Moreover, the index verbal short-term memoryscore (consisting of both Digit Recall and Non-

word Recall) accounted for 11% of the variance inthe Screening score, and the index visual short-term memory score explained 18% of RouteRecall. Fenner, Heathcote, and Jerrams-Smith(2000) showed that children who score low ontasks of visuospatial ability, exhibit more prob-lems with route directions than do children whoscore high on visuospatial tasks. This observationreceives support from the current findings,because the adolescents with mild intellectualdisability clearly had difficulties with BlockRecall, a visuospatial task. However, at the sametime, this finding is also in contrast to ourexpectations, because adolescents with mildintellectual disability, while performing complexeveryday memory tasks, seem to rely on theirshort-term memory rather than on their workingmemory capacity.

The performance of the MA control childrenon the tasks confirmed our expectations: Theyperformed less well on complex everyday memorytasks (i.e., Behavioural Memory Test Screeningand Story Recall) than did the CA control group,and their performance on those tasks was relatedto and even slightly dependent on workingmemory, rs 5 .39 and .45, respectively, and16% of variance in everyday memory wasexplained by working memory.

Adolescents with mild intellectual disabilitydisplay problems with working memory andcomplex everyday memory tasks, more so thanwould be expected on the basis of their MA.Furthermore, studies have shown that although, ingeneral, people rely on their working memorywhen facing complex or novel tasks, adolescentswith mild intellectual disability seem to rely ontheir short-term memory when facing such chal-lenging situations. This might indicate that they areinsufficiently able to use their working memory innew or complex situations; or, alternatively,situations in everyday life might quickly exceedtheir working memory capacity because workingmemory is a weak system for these adolescents(e.g., Van der Molen et al., 2009).

Methods to train memory have been mostfrequently explored in aging populations (withmild cognitive impairment or Alzheimer’s disease;for a review, see Sitzer, Twamley, & Jeste, 2006).Generally, these training programs can be eithercompensatory (i.e., teaching new ways of perform-ing cognitive tasks) or restorative, trying to trainindividuals with weak cognitive abilities. Onaverage, these efforts have resulted in moderate

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effects, with restorative cognitive training strate-gies demonstrating larger effects compared tocompensatory strategies (e.g., Sitzer et al., 2006).We are not aware of similar studies in whichresearchers have explored training effects inadolescents with mild intellectual disability.Everyday memory training could be very helpful,especially when combined with working memorytraining. The latter has already shown beneficialeffects for children with attention deficit hyper-activity disorder (e.g., Klingberg, Forssberg, &Westerberg, 2002) and in adolescents with mildintellectual disability (Van der Molen et al., 2010).

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Received 10/12/07, accepted 9/4/09.Editor-in-charge: Leonard Abbeduto

This research was supported by grants fromStichting Steunfonds ’s Heeren Loo, Stichtingtot Steun VCVGZ and ’s Heeren Loo Kwadrant,the Netherlands. The final author is also affiliatedwith Utrecht University. We are grateful to thechildren who took part in the research as well astheir teachers and school directors for theirsupport. The help of eight students who assistedin collecting the data is gratefully acknowledged.Correspondence regarding this article should besent to Mariet Van der Molen, Utrecht ofAmsterdam, Department of Psychology. Amster-dam, Noord Holland 1018 WB, Netherlands. E-mail: [email protected]

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