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Neuropsychological Differences AmongChildren With Asperger Syndrome,Nonverbal Learning Disabilities,Attention Deficit Disorder, and ControlsMargaret Semrud-Clikeman Ph.D. a , Jenifer Walkowiak b , AlisonWilkinson c & Gina Christopher da Departments of Psychology and Psychiatry, Michigan StateUniversity, East Lansing, Michiganb Children's National Medical Center, Washington, DCc Children's Medical Center Dallas, Dallas, Texasd Department of Educational Psychology, University of Texas atAustin, Austin, TexasPublished online: 16 Aug 2010.

To cite this article: Margaret Semrud-Clikeman Ph.D. , Jenifer Walkowiak , Alison Wilkinson& Gina Christopher (2010) Neuropsychological Differences Among Children With AspergerSyndrome, Nonverbal Learning Disabilities, Attention Deficit Disorder, and Controls, DevelopmentalNeuropsychology, 35:5, 582-600, DOI: 10.1080/87565641.2010.494747

To link to this article: http://dx.doi.org/10.1080/87565641.2010.494747

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Neuropsychological Differences Among ChildrenWith Asperger Syndrome, Nonverbal Learning

Disabilities, Attention Deficit Disorder, and Controls

Margaret Semrud-ClikemanDepartments of Psychology and Psychiatry, Michigan State University,

East Lansing, Michigan

Jenifer WalkowiakChildren’s National Medical Center, Washington, DC

Alison WilkinsonChildren’s Medical Center Dallas, Dallas, Texas

Gina ChristopherDepartment of Educational Psychology, University of Texas at Austin, Austin, Texas

Confusion is present as to possible diagnostic differences between Asperger syndrome (AS) and Non-verbal learning disabilities (NLD) and the relation of these disorders to attentional difficulties.Three-hundred and forty-five children participated in this study in 5 groups; NLD, AS, attention defi-cit hyperactivity disorder (ADHD): Combined type, ADHD: Inattentive type, and controls. The NLDgroup showed particular difficulty on visual-spatial, visual-motor, and fluid reasoning measures com-pared to the other groups. There was also a significant verbal-performance IQ split in this group re-lated to difficulty in social functioning. This study extends the findings from previous studies and ex-tends these findings to differences between AS and NLD groups.

Previous studies have evaluated the neuropsychological functioning of children with nonverballearning disabilities (NLD) (2000), Asperger disorder (AS) (Ozonoff & Griffith, 2000), or atten-tion deficit hyperactivity disorder (ADHD) (Nigg, Blaskey, Huang-Pollock, & Rappley, 2002)Few studies have compared the neuropsychological functioning of children across these diagno-ses in the domains of intelligence, achievement, motor, perception, and fluid reasoning. The pur-pose of this study was to evaluate possible differences among these groups on measures of verbalability, fluid reasoning, and visual-motor skills.

DEVELOPMENTAL NEUROPSYCHOLOGY, 35(5), 582–600Copyright © 2010 Taylor & Francis Group, LLCISSN: 8756-5641 print / 1532-6942 onlineDOI: 10.1080/875656412010494747

Correspondence should be addressed to Margaret Semrud-Clikeman, Ph.D., Michigan State University, PsychologyBuilding, 321 A West Fee Hall, East Lansing, MI 48824. E-mail: semrudcl@msu.edu

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NONVERBAL LEARNING DISABILITY

The original concept of nonverbal learning disabilities was introduced by Johnson and Myklebust(1967) and included children who had difficulty with social perception. Subsequently Rourke andcolleagues later suggested that the combined deficits of visual-spatial learning, tactile and motorskills, and mathematics make up a syndrome they termed a nonverbal learning disability (NLD)(Rourke, 1989; Rourke & Tsatsanis, 1996). An area of controversy in the area of NLD has beenthe definition of this disorder. Many studies utilize an approach where the child must meet a selec-tion of symptoms from an array of possibilities in order to qualify for a diagnosis of NLD. Al-though the NLD subtype continues to be refined, it is currently characterized by three broad areasof dysfunction including motoric skills, visual/spatial organizational skills, and social abilities(Semrud-Clikeman, 2007).

Children with NLD often show excellent single word reading skills and spelling ability buthave difficulty with inferential thinking, complex reading comprehension, and mathematics(Semrud-Clikeman & Glass, 2008). Executive functioning for these children generally may beproblematic as they often have difficulty in understanding situations that involve cause–effectreasoning, generating solutions to problems, and learning new material that is complex or novel(Rourke, 1995; Semrud-Clikeman, 2003).

Many clinicians and researchers suggest that children with NLD have difficulty in correctlyperceiving social relations and with social judgment (Semrud-Clikeman, 2007). Some have sug-gested that these social difficulties are secondary to difficulties with visual-spatial development(Rourke, 2000) while others suggest that there are significant perceptual problems that contributeto problems with understanding facial expressions, voice intonation, and the speaker’s intent(Forrest, 2007; Guli, Wilkinson, & Semrud-Clikeman, 2008; Pennington, 1991, 2008; Semrud-Clikeman, 2007). It is unclear from the empirical literature whether this hypothesis is accurate andfurther research that evaluates whether these perceptual and visual-spatial deficits underlie the so-cial-emotional functioning of children with NLD is needed.

ASPERGER SYNDROME

A defining feature of AS is difficulty with social relationships. Particular difficulties are present innonverbal behaviors (eye contact, facial expression, and body gestures), successful peer relation-ships, and with social reciprocity. Children with AS often have interests that are circumscribedand intense and may be inflexible in their adherence to routines. Neuropsychologically, childrenwith AS show strong verbal skills, poor visual-spatial ability, and problems with executive func-tioning (Klin, Sparrow, Cicchetti, & Rourke, 1995). As some researchers have questioned thefindings of visual-spatial difficulties in AS (Edgin & Pennington, 2005), this area of inquiry re-mains open.

While diagnostic criteria for AS is contained within the DSM-IV-TR (American PsychiatricAssociation, 2000) structure, there is no commensurate manual for a diagnosis of NLD. There areseveral similarities between AS and NLD. In both disorders, problems with social communicationand reciprocity, nonverbal communication, pragmatic language, and visual-spatial skills appearto be present (Gunter, Ghaziuddin, & Ellis, 2002; Voeller, 1995). Stronger verbal compared toperformance skills on cognitive testing were found for children with AS or NLD (Gillberg &

NEUROPSYCHOLOGICAL DIFFERENCES 583

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Billstedt, 2000; Klin et al., 1995). It is important to note that the many of the symptoms of NLDmay be present in children with AS. However, differences between children with AS and thosewith NLD include the presence of stereotyped and restricted patterns of interest and the need toadhere to routines present in children with AS but not NLD (Semrud-Clikeman, 2007).

ADHD, AS, AND NLD

Of interest for this study is the co-occurrence of ADHD in children with AS and NLD (Gillberg &Billstedt, 2000). Studies have found a high co-occurrence of ADHD in a sample of children withAS with 33% to 50% of the samples showing significant difficulties in inattention and 7% show-ing problems with overactivity (Gadow, DeVincent, & Pomeroy, 2006; Ghaziuddin, Weidmer-Mikhail, & Ghaziuddin, 1998; Leyfer et al., 2006; Nyden, Gillberg, Hjelmquist, & Heiman,1999). Similar to children with AS those with NLD also show a tendency to have attentional diffi-culties. Children with NLD are often identified as having problems with attention and tend to bediagnosed with ADHD: Predominately Inattentive type (ADHD–PI) (Semrud-Clikeman, 2007).Some have suggested that the attentional problems found in children with NLD are due to visualperceptual and tactile difficulties (Rourke, 2000) while others suggest these difficulties are sepa-rate but that visual attentional issues may be related to problems with social functioning (Corbett& Constantine, 2006; Fine, Semrud-Clikeman, Butcher, & Walkowiak, 2008). Rourke (2000)suggested that deficits in visual perceptual skills may be related to attentional difficulty seen inmany of these children rather than a true diagnosis of ADHD. Thus, these visual attentional issuesmay have a differential effect on social functioning for children with NLD apart from the difficul-ties found for children with ADHD; an area of inquiry that requires further research.

Given the hypothesis that children with AS or NLD may have attentional differences, it wasfelt important to control for significant attentional problems for these children on the neuro-psychological measures in this study. For this reason we included a group of children withADHD–PI and Attention Deficit Hyperactivity Disorder: Combined type (ADHD–C) to attemptto control the effect attentional difficulties have on the ability to complete tasks that require execu-tive functions. The main hypotheses of this study were that children with AS and NLD wouldshow significant problems on measures of executive functioning, visual perception, and perfor-mance abilities compared to the children with ADHD or the control group. It was also hypothe-sized that children with NLD would show a difference in Verbal-Performance IQ skills comparedto the other four groups as suggested by the literature. Moreover, it was hypothesized that childrenwith NLD would show right-sided difficulties on measures of motor dexterity while these prob-lems would not be present in the children with AS, ADHD–C, ADHD–PI, or controls.

METHOD

Participants

Participants were children referred by parents, teachers, psychologists, psychiatrists, pediatricians,and community organizations to a large university for participation in a larger eight-year study ex-amining the neuropsychological functioning of children with developmental disorders. The finalsample included 345 children ranging in age from 9.1 years to 16.5 years. There were 242 males and

584 SEMRUD-CLIKEMAN, WALKOWIAK, WILKINSON, CHRISTOPHER

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103 females in the sample with 18% of the sample self-identified as a minority (Hispanic, AfricanAmerican, and Asian). There were five groups of children identified for the purpose of this study;control (N = 113), AS (N = 50), NLD (N = 26), ADHD–C (N = 76), and ADHD–PI (N = 80). Re-flecting the general rates of AS and ADHD comorbidity 27 of the AS group also had a secondary di-agnosis of ADHD; 14 with ADHD–C and 13 with ADHD–PI. For the NLD group 22 also had a sec-ondary diagnosis of ADHD; 6 with ADHD–C and 16 with ADHD–PI.

Doctoral-level graduate students trained in administering a comprehensive neuropsycho-logical battery individually assessed the participants. These graduate students were blind to the di-agnosis of the child. Diagnoses were determined by consensus of two independent sources; li-censed psychologists within the community or university, and advanced doctoral students.Participants for whom a diagnosis was not unanimous were not included in the study (N = 5).Exclusionary criteria included a history of a reading disability, seizure disorder, progressive neu-rological problems, traumatic brain injury, or any other serious medical condition. Those withcomorbid psychopathology were also excluded from the sample, including participants with se-vere mood or conduct disorders. Only children with a FSIQ above 80 were included in the sample.

Children with a diagnosis of ADHD were diagnosed by either private practitioners (psychia-trists or psychologists) or through the neuropsychology clinic at the university. Our confirmationof a diagnosis for ADHD required a T-score of 65 or higher on the Behavior Assessment Scale forChildren–2 (BASC–2)(Reynolds & Kamphaus, 2004) inattention and/or hyperactivity scale aswell as meeting criteria for DSM-IV-TR (American Psychiatric Association, 2000) diagnosis ofADHD using a parent semi-structured interview. Children in the control group had no history oflearning, behavioral, or attentional difficulties both by parent and teacher report and an interviewcompleted prior to participation. No child in this group met criteria for AS, NLD, or reading dis-ability.

The Autism Diagnostic Interview (ADI–R) (Le Couteur, Lord, & Rutter, 2003) or the Autism Di-agnostic Observational System (ADOS)(Lord, Rutter, DiLavore, & Risi, 1999) were administered tochildren in the AS group through a private practitioner to determine the presence of autistism spectrumdisorders (ASD). These results were not generally available for the study from these private practitio-ners. No child met the criteria for autism using the ADI–R. The children were diagnosed with ASpartly based on the results of one of these measures with the diagnosis of AS confirmed usingDSM-IV-TR (American Psychiatric Association, 2000) criteria for this study. An AS screener basedon DSM-IV-TR Asperger syndrome criteria developed at the clinic and completed by the child’s pri-mary caretaker was used for tertiary confirmation. The cutoff score on this measure was 6 as definedby DSM-IV-TR criteria. There were three children excluded from the study who did not meet all ofthese criteria. Of the children with AS approximately 25% would also have met criteria for NLD.

An independent licensed psychologist evaluated approximately half of the sample of childrendiagnosed with a nonverbal learning disability. This diagnosis was confirmed through review ofprevious testing if current or through an updated assessment. Agreement among the two first au-thors and any previous diagnosis was required for inclusion in the study. There were six childrenwho were found to not qualify under the following criteria or who met criteria for significant de-pression or anxiety disorder diagnoses. Consistent with the recommendations from research crite-ria (Rourke & Tsatsanis, 1996), children with NLD qualified for this group if they met all of thefollowing criteria: (1)Scores 1 standard deviation below average on the parent form of the SocialSkills Rating Scale (SSRS) (Gresham & Elliott, 1990); (2) Math calculation skills below the 15thpercentile on the math calculation subtest of the Woodcock-Johnson Achievement Test III

NEUROPSYCHOLOGICAL DIFFERENCES 585

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(WJ-Ach III) (Woodcock, McGrew, & Mather, 2001b); (3) Average scores on the letter-wordidentification subtest from the WJ-Ach III (Woodcock et al., 2001b); (4) Average estimated ver-bal IQ of at least 85 standard score points on the Wechsler Abbreviated Scale of Intelligence(WASI) (Psychological Corporation, 1999); (5) Scores at least one standard deviation below aver-age on the Visual Motor-Integration Test (VMI) (Beery, Buktenica, & Beery, 2006); and (6) Be-low average scores on the Purdue Pegboard (Tiffin, 1968). We decided to use a more conservativeapproach to diagnosis and to view the disorder as a syndrome which incorporated the main areasof visual-motor skills, motor skills, social functioning, and good verbal ability.

It is important to mention here that children with AS may have many symptoms that are consistentwith a diagnosis of NLD. For the current study, however, children with AS were selected apart fromsimilarities with the NLD group when one of more of the following symptoms were found during theparent interview: a stereotyped and restricted pattern of interests, inflexible adherence to nonfunc-tional routines, stereotyped and repetitive motor mannerisms, preoccupation with parts of objects, anda lack of spontaneous seeking to share enjoyment, interests, or achievements with others. The childrenin the AS group also were not required to show the same symptoms as detailed above.

Inclusionary Instruments

WASI (Psychological Corporation, 1999). The WASI is an abbreviated scale of intelli-gence with measures of similarities, vocabulary, block design, and matrix reasoning. As discussedearlier, there are research findings that indicate the performance IQ may be impacted in childrenwith NLD. For this reason, the VIQ was used as an estimate of ability.

WJ-Ach III (Woodcock et al., 2001b). Three subtests from the WJ-Ach III were adminis-tered; letter-word identification, calculation, and mathematics reasoning.

VMI (Beery et al., 2006). The VMI requires the child to copy increasingly more difficultgeometric figures within a grid. It provides a measure of visual-motor skills.

Purdue Pegboard (Tiffin, 1968). The Purdue Pegboard requires the child to place pegs inholes as quickly as possible first with the dominant hand, then the nondominant hand, and then bothhands together for 30 seconds each. This measure has been found to be a good measure of manual dex-terity but not necessarily useful for determining lateralization (Reddon, Gill, Gauk, & Maerz, 1988).

The Structured Interview for Diagnostic Assessment of Children (SIDAC) (Puig-Antich& Chambers, 1978). The SIDAC is a formal interview based on DSM-IV diagnoses, modi-fied and updated from the Kiddie-Schedule of Affective Disorders and Schizophrenia (K-SADS)developed by Puig-Antich and Chambers (1978). The ADHD portion of the SIDAC interviewwas used in this study to determine the presence of ADHD symptoms with severity based on thenumber of symptoms reported. Symptoms related to inattention, hyperactivity, and impulsivitywere included. This measure was also used as partial confirmation of parent-reported diagnosis ofADHD, as noted earlier.

Behavior Assessment System for Children–2 (BASC–2) (Reynolds & Kamphaus,2004). Two subtests from the BASC–2 parent rating scale were used as a measure of attentionand hyperactivity. The BASC–2 is an omnibus behavioral rating scale that provides normativedata for specific behaviors. It has excellent psychometric properties.

586 SEMRUD-CLIKEMAN, WALKOWIAK, WILKINSON, CHRISTOPHER

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Social Skills Rating Scale (SSRS) (Gresham & Elliott, 1990). The SSRS is a behav-ioral rating scale completed by the child’s main caretaker. It measures total social skills through aLikert scale of three options (never, sometimes, and very often).

Study Measures

Woodcock-Johnson Cognitive Battery III (WJ-Cog III) (Woodcock, McGrew, & Mather,2001a). Two subtests that make up the Fluid Reasoning index were utilized from the WJ-CogIII; analysis/synthesis and concept formation. These tests require the child to look at a problemand utilize the information present to solve the item. Analysis and synthesis requires the child tosolve picture equations while concept formation requires cognitive flexibility and skill in evaluat-ing problems to determine what is similar between the stimuli.

Rey-Osterreith Complex Figure (Osterreith, 1944). The Rey-Osterreith complex figuretest requires the child to copy a complex figure as accurately as possible and is a measure of per-ceptual organization (Lezak, Howieson, & Loring, 2004). The scoring system used is the one de-veloped by Osterreith and translated by Corwin and Bylsma (1993) involving the widely used18-item, 36-point scoring system.

Judgment of Line Orientation (JLO) (Benton, Sivan, Hamsher, Varney, & Spreen,2004). The JLO is a measure of spatial ability without a motor component. The child is asked tolook at an array of lines and then is shown two lines. He/she is then asked to match the two lines tothe array.

Grooved Pegboard (Klove, 1963). The grooved pegboard measures complex finger co-ordination. It consists of a board with slotted holes angled in various directions. Each peg has agroove and only fits in one way in each hole. The child uses first the dominant hand and then thenondominant hand to place the pegs as quickly as possible. It has been recommended as a goodmeasure of lateralized impairment (Lezak et al., 2004)

Finger Tapping Test (Reitan & Wolfson, 1985). The Finger Tapping test requires thechild to tap a key as quickly as possibly first with the dominant hand and then with thenondominant.

Analyses

Multivariate analysis of variance (MANOVA) with multiple post-hoc comparisons was used todetermine whether there were group differences based on age or verbal IQ in the sample. The gen-eral linear model (GLM) with post-hoc comparisons was used to evaluate group differencesamong the behavioral, cognitive, and neuropsychological measures.

RESULTS

Table 1 presents the group means and standard deviations for the sample age, estimated Verbal IQmeasure, and group selection measures. There were no significant differences among groups for

NEUROPSYCHOLOGICAL DIFFERENCES 587

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age (p = .18). As expected due to selection criteria, there was not a significant difference in esti-mated Verbal IQ among the groups (p = .085, partial eta squared = .024).

Analyses of Group Selection Measures

Membership in groups was partially determined by scores on selected psychological measures.Preliminary analyses were conducted to determine whether the expected group differences werepresent. These results are provided in Table 1.

Visual-Spatial Measures. Scores from the VMI were evaluated using a one way ANOVA.A significant group difference was present for the VMI (F(4,290) = 5.68, p < .0001, partial etasquared = .07). Post-hoc comparisons found that the NLD group differed from all of the othergroups (p < .02). These findings were expected for the NLD group as it was a variable involved inthe selection for the group.

A preliminary analysis of the right (RH), left (LH), and both hands results of the Purdue Peg-board found a significant main group effect difference for all conditions (F(12, 418) = 2.45, p =.004, partial eta squared = .058). Follow-up analyses found that there were significant group dif-ferences for all conditions (p < .008). Post-hoc analysis found that Control group scored betterwith the RH compared to the clinical groups (p < .03). Among the clinical groups there were nodifferences for the RH. For the LH, the AS and NLD groups scored significantly worse than thecontrol group but not from each other (p = .44). This finding was predicted by the selection criteriafor the NLD group. This finding was not predicted for the AS group. For the both hands condition,the AS and NLD groups were significantly less successful than the control group (p < .001) but didnot differ from each other. The NLD group also scored worse compared to the ADHD–C group(p = .03).

Behavioral Measures

On the semi-structured interview (SIDAC) a significant main effect for group was found (F(4,337) = 124.6, p < .0001) for total symptoms of attention/impulsivity/hyperactivity. Post-hoc com-parisons found that the control group scored significantly lower than all clinical groups (p <.0001). Clinical group comparisons found the ADHD–C group to score lower than all other clini-cal groups (p < .0001). There were no significant differences between the AS, NLD, or ADHD–PIgroups.

A preliminary analysis of the hyperactivity and attention scales of the BASC–2 was completedusing a 2 × 5 MANOVA. As expected significant findings were present for the main effect forgroup (F(8, 656) = 47.2, p < .0001, partial eta squared = .37). Follow-up analyses found signifi-cant group differences for attention (p < .0001) and hyperactivity (p < .0001). For the hyperactiv-ity measure, post-hoc analyses found that the ADHD–C group differed significantly from all ofthe other groups (p = .005). When the clinical groups were compared, the ADHD–C showed sig-nificantly higher scores on the hyperactivity measure from all of the other clinical groups (p <.0001) while the AS, NLD, and ADHD–PI groups did not differ from each other. For the attentionmeasure all clinical groups were less successful than the control group (p < .0001). No significantdifferences were found among the clinical groups on the attention measure.

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Social Skills Selection Measure

On the SSRS there was a significant main effect for group (F(4, 329) = 30.2, p < .0001)with the control group scoring significantly higher than all of the clinical groups (p < .0001).There were significant differences between the NLD and ADHD–C group (p = .022) with theNLD group scoring significantly worse than the ADHD–C group. There was no significantdifference between the NLD and AS groups (p = .54). The ADHD–PI group was rated betteron this measure compared to the ADHD–C (p = .014), AS (p < .0001) and NLD (p = .022)groups.

For the AS screener an ANOVA found a significant group difference (p < .0001). Post-hocanalyses found that all of the clinical groups scored higher than the control group (p < .0001).Clinical group comparisons found that the AS group scored higher than the NLD and ADHDgroups (p < .0001). No difference was found among the NLD and ADHD groups (p > .05). Table 1provides these findings

Analysis of Measures of Interest

Evaluation of the estimated verbal and performance IQs using a 2 (verbal, performance) × 5(group) MANOVA found a significant main effect for group (F (8, 678) = 5.769, p < .0001, partialeta = .064). Table 2 provides these results. Follow-up analysis found no significant difference forthe verbal estimated IQ among groups (p = .085, partial eta = .024) with a significant differencepresent for the performance estimated IQ among groups (p < .0001, partial eta = .095). Post-hocanalysis found that the NLD group scored significantly worse than the control group (p < .0001),AS group (p = .001), and both ADHD groups (p < .0001). The AS group scored worse comparedto the control group (p = .018) but not the ADHD groups.

To evaluate whether the difference between verbal and performance estimated IQ differedamong the groups, a one way ANOVA was conducted. A significant group difference was found(F(4, 337) = 6.8, p < .0001, partial eta squared = .075). Post hoc comparisons indicated significantdifferences among the NLD group and all of the other groups with the NLD group showing thelargest split (p < .006). No other group differences were found.

A significant main effect for group was found for academic achievement (F(12, 804) = 6.97, p< .0001, partial eta squared = .084). (See Table 2.) Follow-up analysis found no significant differ-ence for reading recognition among the groups (p = .16) while mathematics calculation (p <.0001) and mathematics reasoning (p < .0001) were significant. Post-hoc analysis found signifi-cant differences among all of the clinical groups and the control group for mathematics calcula-tion (p < .0001) with the control group scoring better. Analysis of the clinical groups found thatthe NLD group performed significantly worse than the ADHD–C (p = .007) and ADHD–PI group(p = .04) on mathematics calculation but not the AS group (p = .16). The ADHD groups did notdiffer from each other (p = .39). The finding of differences for the NLD was not unexpected as itwas one of the criteria for selection for that group. For mathematics reasoning, the control groupperformed significantly better than all of the clinical groups (p < .04). Among the clinical groupsthe NLD group was less successful than the ADHD–C group (p < .0001) and the ADHD–PI group(p = .001) but not the AS group (p = .1). The ADHD groups did not differ from each other signifi-cantly (p = .84).

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Fluid Reasoning Cluster

A significant main effect for group was found on the fluid reasoning measures (F(4, 305) = 8.28, p< .0001, partial eta squared = .1). (See Table 2.) Post-hoc analyses found that the NLD (p < .0001),AS (p < .0001), and ADHD–PI (p = .026) performed significantly worse than the control group onthis measure. Within the clinical groups the NLD group performed significantly worse than theADHD–C (p = .003) and ADHD–PI (p = .006) groups but not the AS group (p = .35). In addition,the AS group differed significantly from the ADHD–C (p = .010) and ADHD–PI (p = .03) groups.The ADHD groups did not differ from each other (p = .72).

When the individual subtests from the fluid reasoning cluster were evaluated a significant dif-ference was found for the analysis/synthesis subtest (p < .0001) and for the concept formationsubtest (p = .001). Post-hoc comparisons for the analysis/synthesis subtest found that the AS,NLD, and ADHD–PI all performed significantly worse than the controls (p < .03) while theADHD–C group did not differ significantly from the control group (p = .06). The NLD groupscored more poorly compared to the ADHD–C group (p = .01) with no other clinical group differ-ences found. On the concept formation subtest there was a significant difference between the AS(p = .005) and NLD (p < .0001) groups and the control group. The NLD group scored significantlymore poorly compared to the ADHD–C (p = .01) and ADHD–PI (p = .01) but not from the ASgroup (p = .12).

Visual-Spatial Abilities

To evaluate group differences on visual-motor and visual-spatial skills a 2 (JLO, Rey-Osterreith)× 5 (group) MANOVA was conducted. A significant main effect for group was present (F(8, 308)= 3.9, p < .0001, partial eta squared = .1). Follow-up analyses found that there was a group differ-ence for the Rey-Osterreith (p = .001) and the JLO (p < .0001). Post-hoc analysis found that theNLD group performed significantly worse than the control (p < .0001), AS (p = .01), and bothADHD groups (p < .0001) on the Rey-Osterreith Complex Figure. There was no significant differ-ence among the other groups. Similarly for the JLO the NLD group performed significantly worsethan all of the groups (p < .001) with no differences found among the other groups. These findingsindicate significantly poorer performance on all measures of visual-organization and visual-spa-tial skills as predicted. To evaluate the relation among the level of social skill development andthese visual-spatial abilities, a correlation was performed. There was a significant overall correla-tion between the JLO and the SSRS social skills rating (p = .013). Similarly there was a significantoverall correlation between the Rey-Osterreith and the SSRS (p = .017).

Motor Skills

To evaluate complex motor skills a 4 (Grooved Pegboard RH, Grooved Pegboard LH, TappingRH, Tapping LH) × 5 (group) MANOVA found a significant main effect for group (F(16, 336) =2.56, p = .001, partial eta squared = .08). Follow-up analyses found significant differences presentfor the Grooved Pegboard RH (p = .002), Grooved Pegboard LH (p = .002), Tapping RH (p = .05),and Tapping LH (p =.02).

Post-hoc analyses found that for the Grooved Pegboard RH the NLD group was significantlyslower than the control group (p = .001) with no significant difference found among the ADHD

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groups, AS group, and the control group (p > .3). The NLD group performed significantly worsethan the ADHD–C (p = .008) and ADHD–PI group (p = .004) with no significance differencefrom the AS group (p = .056). For the Grooved Pegboard LH a significant differences was presentfor the AS (p = .01) and NLD (p = .01) groups compared to the control group.

Post-hoc analysis found that for Tapping LH the AS (p = .009) and NLD (p = .027) groups per-formed significantly worse than the control group. No significant differences were found betweenthe ADHD groups and the control group (p > .4). The AS group performed significantly worsethan the ADHD–C group (p = .01) but not the ADHD–PI group (p = .1) or the NLD group (p = .9).The NLD group performed significantly worse than the ADHD–C group (p = .03) but not theADHD–PI group (.13). No difference was present between the ADHD groups (p = .31).

DISCUSSION

One of the main aims of this study was to determine whether there are neuropsychological differ-ences among children with NLD, AS, or ADHD. A main research question was to explore skillson measures of visual-spatial, fluid reasoning, and motor skills compared to children with AS orADHD. It was hypothesized those children with ADHD–C and ADHD–PI would not show prob-lems in these areas.

Cognitive Differences

The hypothesis that the NLD group would score more poorly on the Performance IQ measurecompared to the other groups was confirmed. The AS group scored more poorly than the controlgroup but not the ADHD groups and there was no difference among the ADHD groups and thecontrol groups on this measure. The NLD group also scored more poorly than the AS group on thePerformance IQ of the WASI. In addition the Verbal-Performance IQ split was found to be signif-icantly larger only for the NLD group. No significant difference between verbal and performanceabilities was present among the other groups. These findings are consistent with those from the lit-erature suggesting the V-P split in children with NLD.

Our study did not select subjects based on this split. We utilized this procedure in order to de-termine whether this split is indeed present in this population. In the NLD sample 74% of the indi-viduals had a V > P split of more than 15 standard score points and 40% had a split of 25 standardscore points or higher (range from 15 to 55). This finding was different for the AS group where63% showed verbal and performance IQs within 15 of each other. However, 37% showed VIQ >PIQ in the AS group.

This finding indicates that while children with NLD are more likely to show a VIQ > PIQ split;there is a sizable minority of children who do not. While this study does find that most childrenwith NLD in our sample did show such a split, this finding is not sufficient to provide a distinctionbetween a diagnosis of NLD and that of AS. Other researchers have reached a similar conclusionwhen looking at children with NLD (Pelletier, Ahmad, & Rourke, 2001).

Conversely, for the AS group there is a sizable minority of children who also show a VIQ >PIQ split. Recently, Black, Wallace, Sokoloff, and Kenworthy (2009) found that children with au-tism with a discrepantly high verbal or performance IQ showed significantly more difficultieswith social functioning. Others have found that when the nonverbal IQ was higher than the verbal

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IQ more social difficulties were present (Joseph, Tager-Flusberg, & Lord, 2002). In the currentstudy a discrepancy between verbal and performance IQ in children with AS was also found withhigher verbal scores related to fewer social difficulties. A future study that evaluated children withNLD may evaluate whether less discrepant measures of ability are related to better outcomes orseverity of the disorder.

Academic findings were also similar to previous studies in that none of the children demon-strated a reading disability. Given that mathematics calculation skills were part of the inclusionarycriteria for our NLD group, it was not surprising that our NLD group scored more poorly on thissubtest (Drummond, Ahmad, & Rourke, 2005; Rourke, Ahmad, Collins, Hayman-Abello, &Warriner, 2002). This finding was also present for the mathematics reasoning subtest and is con-sistent with previous research studies (Pelletier et al., 2001; Strang & Rourke, 1985).

Findings from the measure of fluid reasoning indicated that the control group scored betterthan all of the clinical groups. Of more interest was the finding that both the NLD and AS groupsperformed significantly more poorly compared to the ADHD groups and did not differ from eachother on this measure. Behavioral difficulties are often present for children with NLD or AS whenthey are faced with a novel situation. It may well be that the deficit in fluid reasoning compromisestheir already limited ability to function in unfamiliar or complex situations. Previous studies havesuggested difficulties in concept-formation and novel problem-solving skills (Rourke & Tsatsanis,2000). Other researchers have begun to suggest that the difficulty some children with NLD havein social functioning is due to problems with executive functioning (Forrest, 2007).

Some studies have found that children with ASD may show good to excellent abilities on ameasure of matrix reasoning (Dawson, Soulieres, Gernsbacher, & Mottron, 2007; Hayashi, Kato,Igarashi, & Kashima, 2008). The Raven’s Standard Progressive Matrices Test (Raven, Raven, &Court, 1993) requires the child to solve geometric designs by supplying the missing element bychoosing one of 6 to 8 alternatives that best match the design. This test differs from the WJ-Cog IIImeasures utilized in the current study. The fluid reasoning portion of the WJ-Cog III requires notonly solving of geometric designs but also the use of categorical reasoning, inductive and deduc-tive logic, and the ability to shift set (Strauss, Sherman, & Spreen, 2006). In contrast the Raven’shas been found to be a unidimensional estimate of reasoning ability (Raven, Raven, & Court,2000). The relation of the WJ-Cog III fluid reasoning test to social functioning is likely strongerthan that found for the Raven’s because of the multidimensional nature of social reasoning.

Our findings of difficulty with fluid reasoning for both NLD and AS groups support the sug-gestion that these difficulties complicate the child’s ability to solve novel, visually complex prob-lems. These difficulties may contribute to problems with perspective-taking as well as with theability to adapt to changing environmental demands. Children with ADHD were not found to havesignificant difficulties on this task. This finding suggests that problems encoding visual stimulifor children with AS and NLD contributes to social problems while for children with ADHD so-cial difficulties may not be due to inaccurate perception but rather to impulsivity and inattention(Fine et al., 2008). Further study is necessary to untangle the relation of executive functioning andattention to social competence.

Denckla (2000) suggests that there is a “cognitive overlap zone” of executive functions in NLDand ADHD due to overlapping neural regions. Neuroimaging provides some support for this the-ory. Structural and functional magnetic resonance imaging (fMRI) studies have found differencesin right hemispheric frontal and striatal networks as well as in white matter structures (i.e., corpuscallosum) in children with ADHD (Castellanos et al., 1994; Castellanos et al., 1996; Giedd et al.,

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1994; Hynd et al., 1993; Semrud-Clikeman et al., 2000). Similarly, Rourke (1995) suggested thatdifficulty was present in the right-hemispheric white matter in NLD. Differences have also beenfound in the smaller volume of the corpus callosum for children with AS despite control for whitematter volume (Chung, Dalton, Alexander, & Davidson, 2004), higher volumes of white matter(Filipek, 1999), and increased volume in the caudate regions (Sears et al., 1999). While the emerg-ing MRI research in AS suggests white matter involvement in the disorder, the findings are notconclusive. Prospective research in imaging for children with NLD has not been published butfindings from existing neurological cases does suggest involvement of the right hemisphere andpossibly of white matter (Voeller, 1995). Further study is needed to determine the validity of theright hemispheric white matter hypothesis in NLD.

Visual-spatial differences. The NLD group showed significantly more difficulty com-pared to the other groups on the Rey-Osterreith Complex Figure test. Impairment on this test isthought to reflect problems with planning, organization, and visual-spatial reasoning as well as vi-sual-motor skills. These findings are consistent with previous studies for children with NLD(Wilkinson & Semrud-Clikeman, 2008; Woods, Weinborn, Ball, Tiller-Nevin, & Pickett, 2000;Worling, Humphries, & Tannock, 1999). For the children with AS no significant differences werefound compared to the other three groups. This finding is consistent with that of Edgin and Pen-nington (2005) who found few problems in spatial cognition in children with AS while othershave found problems with visual organization (Kenworthy et al., 2005). These findings indicatedthat copying a complex figure may be an area of specific difficulty for children with NLD. Re-viewing the individual scores supports this hypothesis to some extent. In the NLD sample 63%showed scores in the below average range while for the AS sample 39% scored in the below aver-age range.

Similarly the JLO, a measure of spatial reasoning without a motor component, was found todiffer among the groups. The NLD group scored more poorly compared to the other groups.Children with AS were found to show, as a group, average to above average performance on theJLO (79% of the sample scored within the average to above average range). These visual-spatialmeasures were among the few that differentiated children with NLD from those with AS.

Motor. The literature suggests that a right hemispheric deficit is present in children withNLD and as such more difficulty would be seen with the left hand than the right hand measures. Ithas also been hypothesized that children with NLD show bilateral difficulties in fine motor skills(Rourke, 1995). We found only partial support for this hypothesis. While our findings indicatedthat the NLD and AS groups performed more poorly on a measure of complex fine motor func-tioning compared to controls with the left hand and bilaterally for the NLD group, these measuresdid not differ significantly from the scores obtained by the ADHD groups and as such may not bespecific to AS or NLD.

Limitations of the Study

There are several limitations to this study. One limitation was the lower number of children with adiagnosis of NLD. It required several years to find sufficient numbers of children who met criteriafor NLD who did not also meet criteria for AS. The sample for this study did not include childrenwith genetic or other disorders that have been associated with NLD (velocardiofacial syndrome,Williams syndrome) and these results may not be generalizable to groups of children with medical

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and/or genetic disorders. An additional issue is the possible confound between the visual fluid rea-soning tests of the WJ-Cog III and the visual-perceptual difficulties found in the children withNLD and many of those with a diagnosis of AS. These results should be interpreted in light ofthese problems and our findings are consistent with previous research, also using visual tasks thatfind problems with concept formation and executive functioning (Fisher, DeLuca, & Rourke,1997; Sikora, Haley, Edwards, & Butler, 2002)

Another limitation of the study was that we were not able to obtain the scores from the ADOSor ADI–R. These measures were obtained in a private clinic setting with the results were not avail-able to our study. In the future selection of subjects using these measures would provide for betterdiagnostics and the ability to evaluate performance based on number of symptoms reported on theADI–R.

Finally, our sample of children with NLD did show significant difficulties on the estimatedperformance test from the WASI. It was elected not to use covariate procedures to control for thisgroup difference. There are several articles that question the use of covariate procedures to equategroups (Adams, Brown, & Grant, 1985; Miller & Chapman, 2001) while others suggest thatANCOVAs are appropriate when evaluating treatment decisions (van Breukelen, 2006). In thecase of this study there were no differences in verbal estimated IQ—one of the selection criteria.We elected not to covary for Full Scale estimated IQ which did significantly differ among thegroups due to the group differences on performance estimated IQ given the concerns voiced inthese various articles.

Conclusion

Taken together, these findings indicate that the theoretical model suggested by Rourke (1988)provides a backdrop for our understanding of NLD. The performance deficits seen on the motortasks also suggest bilateral involvement of the brain with the NLD group scoring more poorly onboth right and left hands compared to the other groups. In contrast the AS group only showed dif-ferences with the LH. These findings do suggest difficulties in motor coordination for the NLDand AS groups with poorer performance present for the right hemisphere than for the left. Somehave suggested that children with NLD may appear to be clumsy and uncoordinated (Rourke,1988), while others have found a wide variation in bimanual motor coordination in children withAS (Gunter et al., 2002). Our study suggests that there is a wide variation in these skills for bothgroups and problems with coordination may not be an area specifically different for children withNLD (Wilkinson & Semrud-Clikeman, 2008).

Findings of differences in visual-spatial skills were strongly present for children with NLDeven when motor disability was not present. The finding of differences in visual-spatial skills andperformance abilities implicate the posterior regions of the brain. These difficulties, however,were present only for the NLD group. No difference was found among the AS, ADHD, or controlgroups on visual-spatial ability. This finding suggests that there may be differences between theNLD and AS groups in these areas; an issue that has been the subject of debate in the literature. Itmay well be that the discriminating difference between NLD and AS is in visual-spatial ability,thus it is strongly recommended that these measures to be included in the neuropsychological bat-tery when evaluating these children. A comparison between children with NLD and those diag-nosed with pervasive developmental disorder, not otherwise specified (PDD-NOS) has not beenconducted to determine what commonality may be present. One issue with such a comparison is

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the lack of definition for the diagnosis of PDD-NOS; basically this diagnosis is provided when thechild does not meet criteria for any other diagnosis in the autistic spectrum but has significant so-cial difficulty.

The difference between verbal and performance abilities was found specifically for childrenwith NLD even though the selection criteria had not required such a split. These findings supportclinical reports of larger than expected Verbal-Performance IQ splits in children with NLD. It isimportant to note that a sizable minority of children with AS also showed such a split; thus, thesplit alone is not sufficient for discriminating between NLD and AS for diagnostic purposes. Withlarger numbers in our study these findings may have been more robust. It is difficult, however, torecruit sufficient numbers of well-diagnosed NLD children as it required 7 years of recruiting toobtain our sample size in a large metropolitan region.

While attention is an important issue for children with AS or NLD, it was not strongly related toour measures. One of the issues for our study was attempting to control for attentional problems fre-quently found in children with AS or NLD for which we utilized ADHD–C and ADHD–PI groups.In the future, other studies may wish to contrast children with AS and comorbid ADHD symptoms,those with AS without ADHD symptomatology, as well as that combination for children with NLD.We cannot rule out that attentional issues may have played a role in some of our findings.

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