Carin M. Tillman

Behavioral and ERP indices of response conflict in Stroop and flanker tasks

We investigated effects of different proportions of incongruent trials on behavioral and event-related potential (ERP) interference measures associated with response conflict in the Stroop and flanker task. From the literature, we hypothesized that response conflict is greater when incongruent trials are rare compared to when incongruent trials are frequent. In support, the behavioral results on both tasks and the ERP results on the Stroop task (N450) showed that interference effects were significantly larger when incongruent trials were rare than frequent. In contrast, the ERP results on the flanker task N200 showed a larger interference effect when incongruent trials were frequent than rare. Because results for the flanker N200 were opposite to behavioral effects and theoretical predictions, our findings challenge the notion of the flanker N200 as a valid index of response conflict.

Motor response inhibition and execution in the stop-signal task: development and relation to ADHD behaviors.

The main aim of this study was to investigate the developmental course of motor response inhibition and execution as measured by the stop-signal task in a population-based sample of 525 4- to 12-year-olds. A further aspiration of the study was to enhance the limited knowledge on how the various stop-signal measures relate to ADHD behaviors in a normal sample. We also wanted to contribute to the theoretical understanding of the various stop-signal measures by examining the relations between the stop-signal measures and performance on tasks reflecting other aspects of response inhibition and execution. Our results showed that the ability to inhibit as well as to execute a motor response as measured by the stop-signal task improved with age during childhood. Of specific interest are the findings suggesting that this task captures the development of motor response inhibition in the late preschool years (age 5 years). Both of the inhibition measures derived from the stop-signal task (i.e., SSRT and probability of inhibition) related significantly to teacher ratings of inattention as well as to performance on tasks tapping other aspects of inhibition. The data provided by this study have thus contributed to the scarce knowledge on early development of motor response inhibition, as well as suggested that the stop-signal task may be a valuable tool for capturing deficient motor response inhibition in ADHD behaviors in normal samples.

The relation between working memory components and ADHD symptoms from a developmental perspective.

The objective was to examine the relations between attention deficit hyperactivity disorder (ADHD) symptoms and four working memory (WM) components (short-term memory and central executive in verbal and visuospatial domains) in 284 6–16-year-old children from the general population. The results showed that verbal and visuospatial short-term memory and verbal central executive uniquely contributed to inattention symptoms. Age interacted with verbal short-term memory in predicting inattention, with the relation being stronger in older children. These findings support the notion of ADHD as a developmental disorder, with changes in associated neuropsychological deficits across time. The results further indicate ADHD-related deficits in several specific WM components.

CPT performance, motor activity, and continuous relations to ADHD symptom domains: A developmental study

Using a population-based sample consisting of 401 6- to 12-year-olds, this study examined normative age and sex distributions on motor activity as measured in an actigraphic-based motion tracking system (MTS) and on attention-related functions derived from a Continuous Performance Test (CPT). Specific objectives were to present new knowledge on age-related change in motor activity and to study age effects on changes in motor activity and CPT performance as a function of time on task. Further, continuous relations between the two ADHD symptom domains and CPT performance and motor activity, and importantly, age effects in these relations were examined. CPT performance improved, and level of motor activity decreased with age. Linear associations between the two ADHD symptom domains and several of the CPT and MTS parameters support available research describing the nature of ADHD as a continuous dimension with variable expression throughout the general population. Further, our study is one of the first to provide developmental data using a time on task design, particularly with regard to motor activity. Imperative for ADHD future research are our results showing that age matters in the relation between ADHD behaviours and neuropsychological function.

Effects of Symptoms of ADHD, ODD, and Cognitive Functioning on Social Acceptance and the Positive Illusory Bias in Children

Objective: To examine the effects of symptoms of ADHD and ODD and cognitive functioning on social acceptance and positive bias in children. Method: The sample consisted of 86 children (49 girls) between 7 and 13 years old, recruited to reflect a wide range of ADHD symptoms. Parents and teachers reported on ADHD and ODD symptoms and social acceptance. Children reported on social acceptance and were given tasks measuring working memory, inhibition and reaction-time variability. A discrepancy score between child and adult reports of social acceptance was used as a measure of positive bias. Results: Inattention independently explained variance in social acceptance. The cognitive factors were related to social acceptance and the positive bias, but not beyond the ADHD and ODD symptoms. Conclusion: It is primarily disruptive behavior that contributes to external reports of children’s social acceptance.

Intellectual Deficits in Children with ADHD Beyond Central Executive and Non-Executive Functions

This study aimed to specify the deficit in intellectual ability in children with attention deficit hyperactivity disorder (ADHD), by studying the mediating role of impairments in central executive function (EF)-related components (working memory, inhibition, sustained attention) and non-EFs (short-term memory and processing speed). Two hundred and thirty children aged 8-11 years from a population-based sample were assigned to either the ADHD group, the clinical comparison group, or the normal comparison group. The results showed that children with ADHD had poorer fluid and crystallized intelligence, relative to both comparison groups. Further, regarding fluid intelligence, these deficits were not fully mediated by, but rather went beyond, poorer functioning on the studied EF-related components and non-EFs. We tentatively interpret these fluid deficits in children with ADHD as representing deficiencies in a general intellectual resource reflecting executive attentional processes. Concerning crystallized ability, in contrast, the deficit signified impairment in the studied cognitive functions, as indicated by the significant full mediation effect.

Intelligence and Specific Cognitive Abilities in Children

This community-based study investigated the relationships between measures of specific cognitive functions (such as working memory [WM] and interference control) and intelligence in 283 8- to 11-year-old children, including 124 children who fulfilled criteria for a psychiatric diagnosis. A hierarchical regression analysis was used to overcome issues of overlapping predictor constructs. The results generally showed that measures of processing speed, WM, as well as inhibitory interference control entered in the order of presentation, each contributed uniquely to the explanation of fluid intelligence performance. The results for crystallized intelligence performance generally showed that the measures of processing speed, short-term memory (STM), WM, and sustained attention – entered in that order – made significant independent contributions. While effect sizes varied somewhat for contributions in the whole sample compared with the subgroup not meeting criteria for a psychiatric diagnosis, there were no signi...

The proposed interaction between working memory and inhibition

Two experiments investigated the determinants of performance on a go/no-go task by studying the interplay of two executive function components, working memory (WM) and inhibition. Systematically varied task demands on WM and inhibition were used in the analysis of performance together with individual capacity measures of both functions, thereby investigating an interactive view of WM and inhibition. Further analyses were conducted with individual differences in general fluid intelligence (gF), in an attempt to study the role of higher order cognition in handling task demands. The results are new in presenting empirical evidence for interactive effects of the task demand variables in concert with individual WM capacity as well as with gF, suggesting that executive processes common to WM and gF are involved in inhibitory performance, whereas gF appears to reflect a broader function in controlling behaviour in relation to task goals, whether it involves active responding or not.

A Longitudinal Examination of the Developmental Executive Function Hierarchy in Children With Externalizing Behavior Problems

Objective: Using a 4-year longitudinal design, we evaluated two hypotheses based on developmental executive function (EF) hierarchy accounts in a sample of children with externalizing problems. Method: The participants performed EF tasks when they were between 8 and 12 years (M = 9.93), and again approximately 4 years later when they were between 12 and 15 years (M = 13.36). Results: Inhibition in middle childhood predicted working memory (WM) 4 years later. Further, deficits in inhibition and sustained attention were more prominent in middle rather than late childhood, whereas poor WM was salient throughout these periods. Conclusions: These findings support the hypotheses that EFs develop hierarchically and that EF deficits in ADHD are more prominent in actively developing EFs. They also emphasize ADHD as a developmental disorder.

Developmental Change in the Relation Between Simple and Complex Spans: A Meta-Analysis

In the present meta-analysis the effects of developmental level on the correlation between simple and complex span tasks were investigated. Simple span-complex span correlation coefficients presented in 52 independent samples (7,060 participants) were regressed on a variable representing mean age of sample (range: 4.96-22.80 years), using analyses adapted for meta-analytic purposes. The results showed strong positive relations between mean age of sample and simple span-complex span correlation coefficients, suggesting that the relation between simple and complex span tasks became stronger with increasing age. These results could not be accounted for by study-related differences in measurement reliability, restricted range, or sample size. A new theoretical account explaining these findings is outlined.