Sara T. Kover

A Longitudinal Assessment of Executive Function Skills and Their Association with Math Performance

The present study was designed to examine both concurrent and predictive associations between scores on a measure of executive function (EF) skills, the Contingency Naming Test (CNT), during the early school-age years. A secondary aim of the study was to examine the association between EF skills and mathematics performance. We administered tests of mathematics ability, and the CNT, to 178 children at ages 6 to 7, 8 to 9, and 10 to 11 years. From the CNT we obtained measures of response fluency/efficiency, working memory, and inhibition. The results demonstrate main effects of age on all CNT measures of EF, as anticipated, and inconsistent main effects of gender or mathematics learning disability status. Rates of improvement in EF varied as a function of the working memory demands present during a given task. There were differences in concurrent and predictive correlations for different CNT performance measures. EF scores obtained during the first assessment were as strongly associated with each other as they were with EF scores obtained four years later, suggesting a moderately stable source of individual differences on cognitive performance. EF scores at age 6 to 7 years were associated with concurrent and later mathematics scores, and most of these correlations were stronger than the significant associations found between response fluency on a baseline task (with no working memory demand) and mathematics performance. These findings have implications for the stability of EF skills during the school-age years, and the role of EF in early and later elementary school mathematics performance.

Autism spectrum disorder in children and adolescents with fragile X syndrome: within-syndrome differences and age-related changes.

The Autism Diagnostic Interview-Revised (ADI-R) was used to examine diagnostic profiles and age-related changes in autism symptoms for a group of verbal children and adolescents who had fragile X syndrome, with and without autism. After controlling for nonverbal IQ, we found statistically significant between-group differences for lifetime and current autism symptoms for the Communication and Restricted Interests/Repetitive Behaviors domains, but not the Reciprocal Social Interaction domain. Effect sizes for differences in Reciprocal Social Interaction also were smaller than effect sizes for the other domains, with one exception. Overall, severity of autism symptoms improved with age for all participants, with the least improvement noted for Restricted Interests and Repetitive Behaviors. FMRP did not account for unique variance in autism symptoms over and above nonverbal IQ.

Assessing executive dysfunction in girls with fragile X or Turner syndrome using the Contingency Naming Test (CNT).

The aim of this study was to examine executive function (EF) skills in girls with fragile X or Turner syndrome, using the Contingency Naming Test (CNT). The CNT is a Stroop-like task involving a 1- or 2-attribute contingency rule. We predicted that girls with fragile X would make errors reflecting poor cognitive flexibility and working memory limitations. We predicted that girls with Turner syndrome would have sufficient cognitive flexibility to perform the CNT accurately, but would have difficulty with verbal inhibition and would thus make more self-corrections than girls in a comparison group. The hypotheses were partially supported: relative to their Full Scale IQ-matched comparison group, girls with fragile X or Turner syndrome were slower on the warm-up naming task; girls with fragile X made more errors on the 1-attribute task, and girls with Turner syndrome were less efficient on both the 1- and 2-attribute tasks, without making more self-corrections. These results support previous findings of executive dysfunction associated with fragile X or Turner syndrome. The results suggest that both low IQ and fragile X status contribute to working memory limitations in girls with fragile X and that EF inefficiency in girls with Turner syndrome is due to both working memory limitations and slower response times.

Signaling Noncomprehension of Language: A Comparison of Fragile X Syndrome and Down Syndrome

Signaling noncomprehension of the spoken messages of others was examined for youth with fragile X or Down syndrome in comparison with each other and nonverbal MA-matched typically developing children. A direction-following task was used in which some of the directions were inadequate. Both syndrome groups signaled noncomprehension less often than did the typically developing children. The ability to signal noncomprehension appropriately was related to a measure of receptive vocabulary and syntax. Preliminary analyses indicated that males with fragile X syndrome signaled noncomprehension less often than did their female peers, even after controlling for differences in nonverbal MA.

Establishing Equivalence: Methodological Progress in Group-matching Design and Analysis

This methodological review draws attention to the challenges faced by intellectual and developmental disabilities researchers in the appropriate design and analysis of group comparison studies. We provide a brief overview of matching methodologies in the field, emphasizing group-matching designs used in behavioral research on cognition and language in neurodevelopmental disorders, including autism spectrum disorder, Fragile X syndrome, Down syndrome, and Williams syndrome. The limitations of relying on p values to establish group equivalence are discussed in the context of other existing methods: equivalence tests, propensity scores, and regression-based analyses. Our primary recommendation for advancing research on intellectual and developmental disabilities is the use of descriptive indices of adequate group matching: effect sizes (i.e., standardized mean differences) and variance ratios.

Profiles of Receptive and Expressive Language Abilities in Boys With Comorbid Fragile X Syndrome and Autism

Abstract The authors examined receptive and expressive language profiles for a group of verbal male children and adolescents who had fragile X syndrome along with varying degrees of autism symptoms. A categorical approach for assigning autism diagnostic classification, based on the combined use of the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule (ADOS), and a continuous approach for representing autism symptom severity, based on ADOS severity scores, were used in 2 separate sets of analyses. All analyses controlled for nonverbal IQ and chronological age. Nonverbal IQ accounted for significant variance in all language outcomes with large effect sizes. Results of the categorical analyses failed to reveal an effect of diagnostic group (fragile X syndrome-autism, fragile X syndrome-no autism) on standardized language test performance. Results of the continuous analyses revealed a negative relationship between autism symptom severity and all of the standardized language measures. Implications for representing autism symptoms in fragile X syndrome research are considered.

Investigating Word Learning in Fragile X Syndrome: A Fast-Mapping Study.

Fast-mapping paradigms have not been used previously to examine the process of word learning in boys with fragile X syndrome (FXS), who are likely to have intellectual impairment, language delays, and symptoms of autism. In this study, a fast-mapping task was used to investigate associative word learning in 4- to 10-year-old boys with FXS relative to younger typically developing boys and age-matched boys with autism spectrum disorders (ASD). Task performance exceeded chance levels for all groups; however, boys with FXS outperformed boys with ASD, despite having lower levels of nonverbal cognition. Memory task demands significantly impacted performance only for boys with typical development. For boys with FXS or ASD, fast-mapping uniquely accounted for small but significant variance in concurrent levels of vocabulary comprehension as did chronological age and nonverbal IQ, but not autism severity. Understanding the fast-mapping process has implications for designing interventions to support word learning and language acquisition in these populations.

Autism Symptomatology in Boys with Fragile X Syndrome: A Cross Sectional Developmental Trajectories Comparison with Nonsyndromic Autism Spectrum Disorder

Although males with fragile X syndrome (FXS) are frequently described as demonstrating autism symptomatology, there is much debate regarding whether the behavioral symptoms representing the core domains of autism are the result of the same or different underlying neurological/psychological mechanisms. The present study used a cross-sectional developmental trajectories approach to compare the profiles of autism symptomatology relative to chronological age (CA), nonverbal IQ, and expressive vocabulary ability between individuals with FXS and individuals with nonsyndromic ASD. Results suggest that the onset of autism symptoms and their developmental trajectories in males with FXS differ in important ways as a function of CA, nonverbal cognitive ability, and expressive vocabulary relative to males with nonsyndromic ASD. Theoretical and clinical implications are discussed.

Development of an expressive language sampling procedure in fragile X syndrome: a pilot study.

Objective: There is a great need for valid outcome measures of functional improvement for impending clinical trials of targeted interventions for fragile X syndrome (FXS). Families often report conversational language improvement during clinical treatment, but no validated measures exist to quantify this outcome. This small-scale study sought to determine the feasibility, reproducibility, and clinical validity of highly structured expressive language sampling as an outcome measure reflecting language ability. Methods: Narrative and conversation tasks were administered to 36 verbal participants (25 males and 11 females) with FXS (aged 5–36 years, mean, 18 ± 7 years). Alternate versions were used with randomized task order at 2- to 3-week intervals (mean, 19.6 ± 6.4 days). Audio recordings of sessions were transcribed and analyzed. Dependent measures reflected talkativeness (total number of utterances), utterance planning (proportion of communication [C] units with mazes), articulation (proportion of unintelligible/partly unintelligible C-units), vocabulary (number of different word roots), and syntactic ability (mean length of utterance [MLU] in words). Reproducibility of measures was evaluated with intraclass correlation coefficients (ICC). Results: All participants could complete the tasks. Coded data were highly reproducible with Pearsons correlations at p < .01 for all measures and ICC values of .911 to .966 (conversation) and .728 to .940 (narration). Some measures including MLU and different word roots were correlated with expressive language subscale scores from the Vineland Adaptive Behavior Scale. Conclusions: These expressive language sampling tasks appear to be feasible, reproducible, and clinically valid and should be further validated in a larger cohort, as a promising means of assessing functional expressive language outcomes during clinical trials in FXS.

Sentence Comprehension in Boys With Autism Spectrum Disorder

PURPOSE Previous research has suggested that language comprehension might be particularly impaired in children with autism spectrum disorder (ASD), but this profile has been only broadly characterized. In the current study, the authors examined sentence comprehension in school-age boys with ASD, including a subgroup with intellectual disability (ID), with particular attention paid to errors that might differentiate between lexically and syntactically based difficulties. METHOD Participants were boys with ASD (n = 45, ages 4-11 years) and younger typically developing boys (n = 45, ages 2-6 years). Comprehension was assessed with the Test for Reception of Grammar-Version 2 (TROG-2; Bishop, 2003). Error types were analyzed for a subset of items. RESULTS Boys with ASD did not differ from younger typically developing boys matched on receptive vocabulary in overall sentence comprehension on the TROG-2 or the number of lexical errors committed. In contrast, the subgroup of boys with ASD and ID (n = 16) had poorer overall performance and committed more lexical errors than younger typically developing boys matched on nonverbal cognition. CONCLUSIONS On average, comprehension was delayed in school-age boys with ASD but not beyond receptive vocabulary expectations. Boys with ASD and ID, however, had a weakness in sentence comprehension beyond nonverbal cognitive expectations.