Consequences of Comorbidity of Developmental Coordination … · 2021. 2. 25. · Developmental Coordination Disorders and Learning Disabilities for Severity and Pattern of Perceptual–Motor

JOURNAL OF LEARNING DISABILITIESVOLUME 36, NUMBER 6, NOVEMBER/DECEMBER 2003, PAGES 528–537

Consequences of Comorbidity ofDevelopmental Coordination Disorders and Learning Disabilities for Severity and Pattern of Perceptual–Motor Dysfunction

Marian J. Jongmans, Bouwien C. M. Smits-Engelsman, and Marina M. Schoemaker

Abstract

Children with developmental coordination disorder (DCD) have difficulty learning and performing age-appropriate perceptual–motorskills in the absence of diagnosable neurological disorders. Descriptive studies have shown that comorbidity of DCD exists with attention-deficit/hyperactivity disorder (ADHD) and learning disabilities (LD). This study examined the consequences of the comorbidity of DCDand LD for the severity and pattern of perceptual–motor dysfunction. Compared to children with DCD without LD, children with co-morbid DCD and LD performed lower on a standardized assessment of perceptual–motor ability. Furthermore, it appeared that childrenwith combined DCD and LD have particular difficulty performing manual dexterity and balance tasks but not ball-skill tasks. Implica-tions for understanding the relationship between LD and perceptual–motor problems are discussed. We conclude that the comorbidityof DCD and LD not only affects the severity of perceptual–motor dysfunction but also is associated with a distinctive pattern ofperceptual–motor dysfunction.

The task force responsible forpublishing the third, revisededition of the Diagnostic and

Statistical Manual of Mental Disorders (DSM-III-R; American Psychiatric As-sociation, 1987) included for the firsttime a separate entry for children withdevelopmental perceptual–motor prob-lems. The term chosen to classify thesechildren was developmental coordinationdisorder (DCD; see Note 1). In the Diag-nostic and Statistical Manual of MentalDisorders, Fourth Edition (DSM-IV; Amer-ican Psychiatric Association, 1994), chil-dren with DCD are described as expe-riencing perceptual–motor problemsthat hinder them to such an extent thatthe quality of their academic perfor-mance or activities of daily living areaffected in the absence of any medical

explanation. The prevalence of DCDhas been estimated to be as high as 6%for children in the age range of 5 to 11years (American Psychiatric Associa-tion, 1994), although a large variationin these figures has been reported,from 2.7% in the Netherlands (Van Del-len, Vaessen, & Schoemaker, 1990) to15.6% in Singapore (Wright, Sugden,Ng, & Tan, 1994). The types of motorlearning problems encountered bythese children vary from difficultieswith mastering functional skills, suchas tying shoelaces or riding a bicycle,to difficulties with basic perceptual–motor tasks such as making fast, goal-directed movements (e.g., touching abutton as fast as possible in a reactiontime task; Geuze & van Dellen, 1990;Wilson & McKenzie, 1998). The litera-

ture on children with DCD acknowl-edges that they are a heterogeneousgroup with respect to the profile ofperceptual–motor problems. This hasprompted a search for subtypes to gaina better understanding of possible un-derlying mechanisms of dysfunctionand to provide clues for effective ther-apeutic intervention (e.g., Dewey & Kap-lan, 1994; MacNab, Miller, & Polatajko,2001; Schoemaker, Smits-Engelsman,& Kalverboer, 1997; Smits-Engelsman,Van Galen, & Schoemaker,1997).

The clinical picture that childrenwith DCD present is even more com-plicated because of the frequent co-morbidity of other developmental dis-orders (Dewey & Wilson, 2001; Geuze,Jongmans, Schoemaker, & Smits-Engelsman, 2001; Henderson & Bar-

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nett, 1998). The two most commonlymentioned comorbid disorders areattention-deficit/hyperactivity disor-der (ADHD) and learning disabilities(LD). For example, the rate of comor-bidity between DCD and ADHD hasbeen reported to be approximately 50%(Kadesjö & Gillberg, 1999; Landgren,Petterson, Kjellman, & Gillberg, 1996),and estimates for the rate of comorbid-ity between DCD and LD are of asimilar magnitude (Kaplan, Wilson,Dewey, & Crawford, 1998; Lyytinen &Ahonen, 1989; Silva, McGee, & Wil-liams, 1982). In the past, the termdeficits in attention, motor control, andperception (DAMP) has been applied todescribe children with a combinationof DCD and ADHD (Landgren, Kjell-man, & Gillberg, 1998). Moreover, thethree conditions (DCD, ADHD, andLD) frequently show comorbidity(Dewey, Wilson, Crawford, & Kaplan,2000). It is interesting to observe thatwhereas in the past much effort hasbeen spent on defining discrete diag-nostic categories of children with de-velopmental disorders, the currentwave of observed comorbidity has in-spired some researchers to call for re-considering the validity of discrete de-velopmental disorders. For example,Kaplan et al. (1998) posed the thesisthat “there are no reliably identifiable,discrete developmental disorders be-cause they are all reflections of hetero-geneous, atypical brain development(ABD)” (pp. 484–485). However, beforethe pendulum swings back the otherway, toward an all-inclusive label, it isimportant to establish that childrenwith—at the moment—accepted sepa-rate developmental disorders indeeddo not differ from each other on a num-ber of key characteristics. If they did,this would suggest that, at least for de-scriptive purposes, it is better to keepthe separate diagnostic categories forthe moment.

Whether children with just DCD,ADHD, or LD and children with acombination of any of these develop-mental disorders differ from each otherin terms of the severity and pattern oftheir perceptual–motor dysfunction

has until recently received little atten-tion. Yet, as we have just argued, it isclear that the outcome of such compar-isons is of relevance in establishing thevalidity of separate diagnostic entriesfor these three common developmen-tal disorders. We know of only onestudy that has asked the question ofwhether perceptual–motor problemsin children with DCD and childrenwith both ADHD and DCD (DAMP)share a common underlying deficit(Pereira, Landgren, Gillberg, & Forss-berg, 2001). Children with either iso-lated DCD or DAMP were assessed ona task measuring the coordination ofgrip force and load force requiredwhile lifting a small weight. It wasshown that both groups failed to reachthe age norm for the coordination pat-tern of grip force and load force spe-cific for a grip–lift synergy. However,children with isolated DCD did notdiffer from children with a combina-tion of DCD and ADHD in the controlof grip force, suggesting similarperceptual–motor control problems onthis task in both groups.

Experimental or descriptive studiesseparating the performance of childrenwith DCD with and without LD inorder to study perceptual–motor pro-files in the same way as the aforemen-tioned studies on DCD and ADHDhave not, to our knowledge, beenundertaken. The aims of the presentstudy were to investigate whetherthere is a difference in the severity ofperceptual–motor problems encoun-tered by children with DCD with andwithout concomitant LD and to deter-mine whether there is a difference inthe pattern of perceptual–motor dys-function between children with DCDwith and without concomitant LD.

Method

Participants

Data collected on 749 children rangingin age from 4 to 13 years were used forthis study. The children were recruitedacross the whole of the Netherlands

(n = 594) and a part of Germany nearthe Dutch–German border (n = 155; seeNote 2). The data set consisted of twogroups of children: a randomly se-lected group of 535 children who tookpart in a study to establish Dutchnorms for a test of perceptual–motorfunction, the Movement AssessmentBattery for Children (MABC; Smits-Engelsman, 1998), and a group of 214children who had been referred bytheir physician to a pediatric physicaltherapist for further examination andtreatment of suspected perceptual–motor problems. The large majority ofthe children (n = 602; 80%) attendedschools for general education. The re-mainder of the sample (n = 147; 20%)attended Dutch schools for childrenwith special educational needs. Until2001, admission to special education inthe Netherlands was decided by acommittee consisting of at least theschool principal, a medical doctor, awelfare worker, and a psychologist oran educator. The admission process in-cluded administering psychologicaland academic achievement tests to thechild. If the child’s needs lay in themotor domain (e.g., cerebral palsy,muscular dystrophy) he or she wasoffered a place at a so-called Mytylschool (i.e., a school for children with aphysical disability). Children withouta physical disability with an aver-age IQ of 60 to 80 were placed in a so-called MLK school (i.e., a school for children with educable mental re-tardation). Children with learning andpedagogic problems and an IQ of 80 orhigher were placed in a so-called LOMschool (i.e., a school for children with alearning disability). A learning disabil-ity was diagnosed when academicachievement was significantly (2 years)behind that expected in relation to IQin the absence of explanatory factors,such as physical or sensory (auditoryor visual) impairments or social con-text factors (i.e., poor education or lackof opportunity). All children partici-pating in the current study attended aLOM school. No data were availableon the ethnic origin or socioeconomicbackground of the children.


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For the current study, children wereclassified as having DCD if they metthe criteria described in the DSM-IV:

1. Performance in daily activities thatrequire motor coordination is sub-stantially below that expectedgiven the person’s chronologicalage and measured intelligence.This may be manifested by markeddelays in achieving motor mile-stones (e.g., walking, crawling, sit-ting); dropping things; clumsiness;poor performance in sports; orpoor handwriting.

2. The disturbance in Criterion 1 sig-nificantly interferes with academicachievement or activities of dailyliving.

3. The disturbance is not due to ageneral medical condition (e.g.,cerebral palsy, hemiplegia, muscu-lar dystrophy) and does not meetthe criteria for Pervasive Develop-mental Disorder.

In other words, children with a totalscore on the MABC below the 15th per-centile (Criterion 1) who were referredto a pediatric physical therapist fortheir perceptual–motor problems (Cri-terion 2) without an observable,known neurological disorder (Crite-rion 3) were assigned to the DCDgroup. The inclusion criteria for theDCD group stipulated that the partici-pants did not have any indication of aneurological or physical impairment.

Children attending special educa-tion were classified as children with

LD. Not enough data were available onthe children attending special educa-tion schools to classify them accordingto the DSM-IV criteria for reading,spelling, writing, or arithmetic disor-ders. However, children attendingDutch schools for LD in general expe-rience difficulty with basic reading andlanguage skills (80%) notwithstandingaverage IQ (above 80). Problems withmathematics also occur but are lesscommon. Children with mental retar-dation, autism, deafness, blindness,and severe behavioral disorders attenddifferent types of schools for specialeducation in the Netherlands. No datawere available on the presence or ab-sence of behavioral or conduct disor-ders (e.g., ADHD).

The procedure just described led tothe formation of four groups of chil-dren: children without DCD and with-out LD (Group 1; n = 545); childrenwithout DCD but with LD (Group 2; n = 94); children with DCD but with-out LD (Group 3; n = 57); and finally,children with both DCD and LD(Group 4; n = 53). Table 1 presents theage and gender distributions in eachgroup. A univariate general linearmodel showed a main effect of age, F(3,745) = 2.68, p = .046, adjusted R2 for cor-rected model = .007, but post hoc mul-tiple comparisons showed no signifi-cant differences between any of thegroups. Chi-square analyses revealedan overall difference in the proportionof boys between the groups, χ2(3, N =437) = 33.82, p < .001. Partitioned chi-square analyses showed a linear in-

crease in the proportion of boys fromthe no DCD/no LD group to the DCD + LD group.

Measures

All children were assessed on theMABC (Henderson & Sugden, 1992).This test provides an indication of achild’s motor functioning across fineand gross motor tasks. Performance isrelated to norms using age-dependentstandardized scores for children ages 4to 12 years. There are four age bands.Age Band 1 covers the ages of 4 to 6years, Age Band 2 is for children ages7 and 8 years, Age Band 3 for childrenages 9 and 10 years, and Age Band 4 forchildren ages 11 and 12 years. For eachage band, the test consists of eightitems measuring different aspects ofperceptual–motor ability; three itemsmeasure manual dexterity, two itemsmeasure ball skills, and there are threeitems for evaluating balance. The firstmanual dexterity item (MD1) seeks tomeasure the speed and sureness ofmovement by each hand separately.The second manual dexterity item(MD2) was designed to measure thecoordination of two hands for per-forming a single operation, whereasthe third manual dexterity item (MD3)assesses hand–eye coordination as re-quired in the control of a pen or pencil.The first ball-skill item (BS1) looks at achild’s ability to accurately propel anobject into space, and the second ball-skill item (BS2) challenges the child tocatch a moving object. The three bal-ance items are divided into one staticbalance item (assessing static control;SBAL) and two dynamic balance itemsassessing fast and explosive move-ments (DBAL1) and slow and con-trolled movements (DBAL2), respec-tively. The eight tasks of the MABCwere administered in the aforemen-tioned order.

Children can score between 0 and 5on each item. The higher the score, thepoorer the performance. Three sub-scale scores are calculated by addingthe three manual dexterity items(range = 0–15), the two ball-skill items

TABLE 1Age and Gender Distribution Across Participant Groups

Characteristic No DCD/no LDa LD onlyb DCD onlyc DCD + LDd

Age (mos.)M 95.63 100.66 93.25 103.83SD 26.65 27.65 22.07 21.04

GenderBoys/girls (n) 284/261 66/28 44/13 43/10Boys (%) 52 70 77 81

Note. DCD = developmental coordination disorder; LD = learning disabilities.an = 545. bn = 94. cn = 57. dn = 53.



(range = 0–10), and the three balanceitems (range = 0–15). Total scores canvary from 0 to 40 and can be trans-formed to percentile scores showingthe child’s level of performance incomparison to that of peers. In thepresent study, the 15th percentile wasused as a cutoff criterion for totalscores between typical and borderline/deviant motor performance. Accord-ing to the data from the Dutch stan-dardization of the MABC, the U.S.norms are valid for the Dutch popula-tion (Smits-Engelsman, 1998). There-fore, these norms will be used in thepresent study. According to the MABCmanual, the test has acceptable valid-ity and reliability (see also Lam & Hen-derson, 1987). Interrater reliability forthis test ranges from .70 to .89, andtest–retest reliability is .75 (Henderson& Sugden, 1992).

Statistical Analysis

To investigate the effect of various fac-tors, univariate or multivariate generallinear models (GLM) were used whereappropriate. Post hoc tests consisted ofmultiple comparisons using the Bon-ferroni method. Furthermore, logisticregression analysis was performed todetermine which MABC test items bestpredicted whether a child belonged tothe group of children with only DCDor the group of children with comorbidDCD and LD. An alpha level of .05 wasused throughout the study.

Results

Severity of Perceptual–MotorProblems

A univariate GLM with MABC meantotal score as the dependent variableand presence/absence of LD, presence/absence of DCD, gender, and age band(see Note 3) as factors was performed(adjusted R2 = .543 for corrected model).This showed a main effect of presence/absence of LD, F(1, 732) = 89.80, p <.001, partial η2 = .109; children with LD obtained significantly higher MABCtotal scores compared to children with-

out LD (M = 14.30, SD = 9.68, vs. M = 5.81, SD = 5.38, respectively). Also,a main effect of presence/absence ofDCD was found, F(1, 732) = 340.37, p <.001, partial η2 = .317; children withDCD obtained a higher mean MABCtotal score compared to children with-out DCD (M = 19.08, SD = 7.42, vs. M = 5.48, SD = 5.05, respectively). Fur-thermore, a main effect of age bandwas noted, F(2, 732) = 14.56, p < .001,partial η2 = .038; children in the oldestage band (the combined Age Bands 3and 4) obtained a significantly highermean score (M = 8.92, SD = 8.08) com-pared to children in either Age Band 1(M = 6.73, SD = 6.85) or Age Band 2 (M = 6.71, SD = 6.52). The main effectof gender was not significant, F(1, 732) = .102, ns.

Three interactions were noted. First,the interaction between presence/absence of LD and age band was sta-tistically significant, F(2, 732) = 7.29, p = .001, partial η2 = .020 (see Figure 1).This interaction was further examinedby means of one-way ANOVAs. Thisrevealed that whereas the difference inmean MABC total scores did not reachstatistical significance among childrenof various ages without LD, F(2, 599) =1.81, p = .164, it did among children

with LD, F(2, 144) = 3.85, p = .024. Sub-sequent post hoc analyses revealedthat the oldest children with LD ob-tained significantly higher mean scorescompared to younger age band groupswith LD (p < .001).

The second interaction concernedthe relationship between presence/absence of LD and gender, F(1, 732) =7.32, p = .007, partial η2 = .010 (see Fig-ure 2). Subsequent t tests showed thatwhereas there was a statistically signif-icant difference in performance be-tween boys and girls without LD (boysM = 6.73, SD = 5.87, vs. girls M = 4.71,SD = 4.51; t[596] = 4.76, p < .001), thisdifference no longer reached statisticalsignificance among children with LD(boys M = 14.59, SD = 9.60, vs. girls M = 13.46, SD = 9.98; t[145] = 0.62, ns).

The third interaction concerned therelationship between presence/absenceof LD and presence/absence of DCDwith regard to MABC total scores, F(1,732) = 3.84, p = .050, partial η2 = .005(see Figure 3). Further examination ofthis interaction by means of t tests re-vealed that among the children with-out DCD, the mean total scores of chil-dren with and without LD differedsignificantly, t(104) = −6.67, p < .001.Similarly, children with and without

FIGURE 1. Mean MABC total scores for children of different age bands with and without LD. MABC = Movement Assessment Battery for Children (Smits-Engelsman, 1998); LD = learning disabilities.



LD among the children with DCD dif-fered significantly from each other inmean total score, t(82) = −4.74, p < .001.

Tables 2 and 3 show the mean scoreson the MABC for the four groups ofchildren. From Table 2, it appears thatthere is a rise in mean total MABC

score across the four groups; childrenin the no DCD/no LD group obtainedthe lowest (i.e., least atypical) meantotal score, followed by children in theLD-only group, DCD-only group, andDCD + LD group. This linear increasein mean total MABC score was con-

firmed by means of a univariate GLM,treating group as a between-participantsfactor, F(3, 745) = 265.43, p < .001, par-tial η2 = .517, followed by post hocanalyses (all ps < .001).

Pattern of Perceptual–MotorProblems

A logistic regression analysis showedthat a model containing MABC Dy-namic Balance Item 2 (DBAL2; exp[β] =1.54, df = 1, p < .001) and Manual Dex-terity Item 1 (MD1; exp[β] = 1.53, df = 1, p = .002) significantly predictedwhether a child belonged to the DCD-only or to the DCD + LD group, χ2(2, N = 110) = 29.24, p < .001. The higherthe scores of a child on these two items,the more likely the child belonged tothe DCD + LD group. Using these twoitems, 74% of the children with DCDand 70% of the children with comorbidDCD and LD were correctly classified(overall correctly classified 72%).

Discussion

It has previously been shown that chil-dren with DCD are heterogeneous notonly with respect to their perceptual–motor profile of dysfunction but alsowith respect to the presence or absenceof concomitant developmental disor-ders such as ADHD or LD (e.g., Missi-una, 2001; Sugden & Wright, 1998). Thepresent study shows that if concomi-tant LD is present in children withDCD, the severity of perceptual–motordysfunction increases. Furthermore, aclear difference in the children’s pat-tern of perceptual–motor dysfunctionemerged; children with a combinationof DCD and LD scored particularlylow on tasks measuring dynamic bal-ance and unimanual dexterity com-pared to their peers with only DCD.

However, in the present study, thedivision between the presence or ab-sence of a learning disability waspurely based on whether the child wasa student in a school for special educa-tion. It could be argued that childrenwho showed a similar type and level of

FIGURE 2. Mean MABC total scores for boys and girls with and without LD. MABC = Movement Assessment Battery for Children (Smits-Engelsman, 1998); LD = learning disabilities.

FIGURE 3. Mean MABC total scores for children with and without LD among chil-dren with and without DCD. MABC = Movement Assessment Battery for Children(Smits-Engelsman, 1998); LD = learning disabilities; DCD = developmental coordi-nation disorder.



LD but who did not attend specialeducation might show less comorbidperceptual–motor problems than wereport here. Although it is not possibleto rule out such a selection bias, at thetime this study was conducted, we feltit was not very likely that children whoshowed a type and level of LD compa-rable to that of children attendingschools for special education wouldnot attend such a school in the Nether-lands. Nevertheless, the referral crite-ria to special education schools mighthave possibly led us to observe anincreased level of perceptual–motordysfunction and a rather specific pat-tern of such dysfunction. Therefore,our results need to be confirmed in astudy in which inclusion in the groupof children with LD is solely based onthe outcome of individual assessment.

The increasing interest in and recog-nition of DCD not only in North Amer-ica but also in European countries hasgiven a new impetus to the long-standing discussion regarding the rela-tionship between perceptual–motorproblems and LD (Maeland & Sovik,1993; Martini, Heath, & Missiuna,1999). The rate of comorbidity betweenDCD and LD observed in the presentstudy, in which 48% of children withDCD also attended schools for specialeducation, is similar to the rate re-ported earlier (Kaplan et al., 1998). Froma reverse perspective, 36% of childrenattending schools for children withspecial educational needs were identi-fied as having DCD. This is also inclose agreement with earlier observa-tions (e.g., Sugden & Wann, 1987). Ithas been reported for some time thatchildren with LD perform significantlylower than their peers without LD alsoin their motor skills (e.g., Dobbins,Garron, & Rarick, 1981; Rarick, Dob-bins, & Broadhead, 1976; Sugden &Wann, 1987). We were able to confirmthese findings by showing that even ifchildren with DCD were excludedfrom the LD group, the remaining chil-dren in the LD-only group still per-formed significantly lower than chil-dren in the no DCD/no LD group.Apparently, the difficulty these chil-

dren have with acquiring academicskills extends to the area of motorlearning, even though it is not severeenough to be labeled as problematic.

Compared to children with onlyDCD or children with only LD, theperformance in the motor domain ofchildren with concomitant perceptual–motor and learning problems wasmore severely affected. We were un-able to investigate whether these chil-dren also showed more severe learningdisabilities as compared to the childrenin the LD-only group, but we hypoth-esize that this could be the case. Fur-thermore, we acknowledge that if wealso had known which of the childrenmet the full DSM-IV criteria for ADHD,probably even more interesting rela-tionships would have emerged.

It was interesting to observe thatchildren in the DCD + LD group werenot simply performing lower on alleight items of the MABC compared tochildren in the DCD-only group. In-stead, two test items stood out as beingparticularly difficult to perform for chil-dren in the comorbid group. The taskthat differentiated these two groups

best was designed to measure the abil-ity of controlling the whole bodyduring a nonstatic balance position(DBAL2). Depending on the age of thechildren, the tasks included in theMABC to evaluate this ability involvewalking on tiptoe over a line (AgeBand 1), walking in a heel–toe gait overa line forward (Age Band 2), walkingin a heel–toe gait backward (Age Band3), and balancing a tennis ball on aboard while walking (Age Band 4).None of these tasks impose a time con-straint on the children. Three times asmany children in the DCD + LD groupfailed to reach an age-appropriate per-formance level as children in the DCD-only group, who performed similar tochildren in the LD-only group. Thesecond-best task to distinguish be-tween the groups was the task measur-ing unimanual dexterity (MD1). Thiswas a Peg-Board task requiring fast,goal-directed movements with the pre-ferred and nonpreferred hand. From amotor control and information pro-cessing viewpoint, this is a rather com-plex task, requiring ballistic move-ments to visually located targets (holes)

TABLE 2MABC Total Scores and Subscores and Percentage of Children Scoring Below

15th Percentile by Group

Score No DCD/no LDa LD onlyb DCD onlyc DCD + LDd

TotalM 4.73 9.79 16.08 22.30SD 4.17 7.14 4.83 8.36% 9 32 100 100

Manual dexterityM 1.85 4.44 7.11 9.63SD 2.25 4.09 3.27 3.68% 8 34 70 85

Ball skillsM 1.44 1.81 3.76 5.47SD 1.82 2.09 2.61 2.80% 21 24 67 83

BalanceM 1.45 3.66 5.18 7.36SD 2.26 3.47 3.16 4.64% 6 27 46 62

Note. MABC = Movement Assessment Battery for Children (Smits-Engelsman (1998); DCD = developmen-tal coordination disorder; LD = learning disabilities.an = 545. bn = 94. cn = 57. dn = 53.



and between-finger manipulation (pin)with high endpoint accuracy.

Several plausible neuropsychologi-cal explanations have been put for-ward for the co-occurrence of DCD andLD. Support for a significant relationbetween motor skill performance andlanguage has been provided by a num-ber of studies (Bradford & Dodd, 1996;Cermak, Ward, & Ward, 1986; Hill, 1998,2001; Notherdaeme, Amorosa, Ploog,& Scheimann, 1988; Owen & McKinlay,1997; Sommers, 1988; Tallal & Stark,1982). The nature of this relation, how-

ever, has seldom been pursued in depth.Is this relation causal (i.e., does poormotor development influence the de-velopment of language, or vice versa),or is the putative relation an artifact ofcritical neurological variables underly-ing both motor and language impair-ment? Two hypotheses have been pur-sued in the literature concerning thesearch for such an underlying com-monality: the cerebellar and the inter–intrahemispheric deficit hypothesis.

Although there is undoubtedly con-siderable heterogeneity in the skills of

children with dyslexia, the general typeof performance difficulty these chil-dren have involves difficulties whenrequired to undertake fast, fluent,overlearned skills or novel skills thatinvolve the blending of two actions.These problems in motor learning andautomatization point to the cerebel-lum, which has been traditionally con-sidered a motor area (Eccles, Ito, &Szentagothai, 1967; Holmes, 1917, 1939).However, there is now overwhelmingevidence of the importance of the cere-bellum in language (Ackermann & Her-trich, 2000; Allen, Buxton, Wong, &Courchesne, 1997; Fabbro, Moretti, &Bava, 2000; Leiner, Leiner, & Dow, 1989;Silveri & Misciagna, 2000; Thach, 1996),including a recent demonstration ofspecific cerebellar involvement in read-ing (Fulbright et al., 1999). Moreover,Fawcett and colleagues showed arange of classic cerebellar signs in chil-dren with dyslexia (Fawcett & Nicol-son, 1999; Fawcett, Nicolson, & Dean,1996).

The inter- and intrahemispheric def-icit hypotheses were also suggested asplausible neuropsychological explana-tions for the co-occurrence of languageand motor impairments. Sigmundssonand colleagues (Sigmundsson, Ing-valdsen, & Whiting, 1997a, 1997b; Sig-mundsson, Whiting, & Ingvaldsen,1999) stated that the co-occurrence ofhand–eye coordination problems anddyslexia could be the behavioral man-ifestation of putative neurological dis-orders related to an intrahemisphericor interhemispheric disconnection.Post hoc analysis of the performancewith the preferred and nonpreferredhand in the present study did not pointin the direction of an interhemisphericdisconnection phenomenon, as theperformance of the nondominant handwas not especially lower for the LD,DCD, or DCD + LD groups. Intra-hemispheric dysfunction could not betested with our data, but studies ofparticipants with dyslexia have sug-gested that they may be unable toprocess fast incoming sensory infor-mation adequately in any domain,both visual and kinesthetic, within the

TABLE 3Means, Standard Deviations, and Percentage of Children Scoring Below

15th Percentile for Individual MABC Test Items

Item No DCD/no LDa LD onlyb DCD onlyc DCD + LDd

MD1M 0.70 1.60 2.33 3.52SD 1.13 1.72 1.70 1.54% 15 39 58 87

MD2 M 0.60 1.41 2.25 2.85SD 1.20 1.72 1.90 1.88% 15 35 58 68

MD3 M 0.55 1.32 2.56 3.23SD 1.10 1.87 1.94 1.85% 13 27 63 75

BS1 M 0.67 1.09 1.90 3.08SD 1.18 1.46 1.72 1.71% 16 31 49 74

BS2M 0.78 0.72 1.84 2.40SD 1.23 1.22 1.82 1.94% 23 17 46 55

SBALM 0.70 1.45 2.48 3.00SD 1.20 1.58 1.69 1.66% 17 38 65 75

DBAL1 M 0.56 1.15 1.75 1.81SD 1.35 1.65 2.19 2.21% 16 33 39 43

DBAL2M 0.19 1.04 0.94 2.54SD 0.76 1.72 1.68 2.01% 5 28 21 62

Note. MABC = Movement Assessment Battery for Children (Smits-Engelsman, 1998); DCD = developmen-tal coordination disorder; LD = learning disabilities; MD1 = Manual Dexterity subscale Item 1, etc.; BS1 =Ball Skills subscale Item 1, etc.: SBAL = Static Balance item; DBAL1 = Dynamic Balance Item 1, etc.an = 545. bn = 94. cn = 57. dn = 53.



same modality (intramodal) and be-tween modalities (intermodal). Theparietal lobe in particular is thought tobe necessary to monitor efference copyreceived from downstream motor out-put areas (Sirigu et al., 1995, 1996).Anatomical, electrophysiological, psy-chophysical, and brain-imaging stud-ies have all contributed to elucidatingthat in children with reading disabili-ties, visual confusions relate to abnor-malities of the magnocellular compo-nent of the visual system. This system,which plays an important role in guid-ing visual attention, is specialized forprocessing fast temporal informationand culminates in the posterior pari-etal cortex (Stein, 2001).

The pattern of perceptual–motordysfunction found in our study cor-roborates motor symptoms most men-tioned in children with LD. These chil-dren did not score high on hand–eyecoordination when required to movefast and accurately, which may be dueto problems with processing fast in-coming sensory information, whichalso supports an intrahemisphericdeficit hypothesis. However, problemswith making fast, fluent, reciprocalmovements and balance could also pointto cerebellar involvement. More exper-imental work is required to disentan-gle these underlying processes.

We conclude that among childrenwith DCD, the presence of concomitantLD not only increases the likelihood of low performance on perceptual–motor tasks that are part of many dailymotor activities but also involves a dis-tinct pattern of perceptual–motor dys-function characterized by problemswith fast, goal-directed movementsand keeping balance while movingaround. These findings argue in favorof keeping DCD and LD as separate di-agnostic categories for the time being,because children fulfilling the criteriafor these developmental disorders areclearly distinguishable in terms of theirperceptual–motor abilities. Finally, theimpact of poor manual dexterity andbalance is not to be underestimated, asa large number of children with LD arelikely to pursue vocational training,

where these abilities are mandatory.

ABOUT THE AUTHORS

Marian J. Jongmans, PhD, is a professor ofspecial education at Utrecht University, theNetherlands. Her current interests include thedevelopment of young children with motor orcognitive disabilities. Bouwien C. M. Smits-Engelsman, PhD, is a lecturer of developmen-tal human movement science, head of postgrad-uate education in physiotherapy at HogeschoolBrabant Bedrijfsopleidingen, and a senior re-searcher at the Nijmegen Institute for Cognitionand Information, University of Nijmegen, theNetherlands. Her current interests include de-velopmental changes in motor control and mo-tor learning. Marina M. Schoemaker, PhD, isa senior lecturer at the Institute of HumanMovement Sciences, University of Groningen,the Netherlands. Her current interests are inmotor development and disorders of motor con-trol in children. Address: Marian J. Jongmans,Faculty of Social Sciences, Department of Gen-eral and Special Education, Utrecht University,Heidelberglaan 1, 3524 CS Utrecht, the Nether-lands; e-mail: [email protected]

NOTES

1. Not long thereafter, the World Health Orga-nization also recognized the importance ofestablishing an entry for children with spe-cific developmental disorder of motorfunction (ICD-9; World Health Organiza-tion, 1992). However, a consensus meetingheld in 1994 in London, Ontario, Canada,concluded that DCD should be the preferredterm (Polatajko, Fox, & Missiuna, 1995).

2. No statistically significant differences werenoted between these two geographic sampleson MABC scores, and they were, therefore,combined.

3. The data of the children in Age Band 3 and4 were collapsed because of very low Ns inthe DCD-only and DCD + LD groups testedon Age Band 4 (N = 2 and N = 5, respec-tively).

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