Controlled processing and vigilance in hyperactivity: time will tell

Neuropsychopharmacological mechanisms of stimulant drug action in attention-deficit hyperactivity disorder: a review and integration

The psychostimulants, D-amphetamine (D-AMP) and methylphenidate (MPH), are widely used to treat attention-deficit hyperactivity disorder (ADHD) in both children and adults. The purpose of this paper is to integrate results of basic and clinical research with stimulants in order to enhance understanding of the neuropharmacological mechanisms of therapeutic action of these drugs. Neurochemical, neurophysiological and neuroimaging studies in animals reveal that the facilitative effects of stimulants on locomotor activity, reinforcement processes, and rate-dependency are mediated by dopaminergic effects at the nucleus accumbens, whereas effects on delayed responding and working memory are mediated by noradrenergic afferents from the locus coeruleus (LC) to prefrontal cortex (PFC). Enhancing effects of the stimulants on attention and stimulus control of behavior are mediated by both dopaminergic and noradrenergic systems. In humans, stimulants appear to exert rate-dependent effects on activity levels, and primarily enhance the motor output, rather than stimulus evaluation stages of information-processing. Similarity of response of individuals with and without ADHD suggests that the stimulants do not target a specific neurobiological deficit in ADHD, but rather exert compensatory effects. Integration of evidence from pre-clinical and clinical research suggests that these effects may involve stimulation of pre-synaptic inhibitory autoreceptors, resulting in reduced activity in dopaminergic and noradrenergic pathways. The implications of these and other hypotheses for further pre-clinical and clinical research are discussed.

The concomitance of learning disabilities and emotional/behavioral disorders: a conceptual model

Although research has documented overlapping and coexisting characteristics of learning disabilities and emotional/behavioral disorders, little attention has been paid to the subset of students who manifest symptoms of both disorders (LD/EBD). This gap in our professional knowledge/research base may be due to (a) exclusive language in federal definitions that promotes differentiation of disabilities rather than recognition of symptom overlap; (b) the lack of a conceptual model of concomitant learning and emotional/behavioral disorders; and (c) the absence of a research focus on this population. In this article, we construct a conceptual model involving six critical domains of relevance to students with LD/EBD. After describing the utility of this interactive and functional model, we highlight critical issues in screening, assessment, and programming for children with concomitant LD/EBD.

Error patterns on the continuous performance test in non-medicated and medicated samples of children with and without ADHD: a meta-analytic review

We systematically reviewed the patterns of Continuous Performance Test (CPT) errors of omission and commission exhibited by normal children and children with Attention Deficit and Hyperactivity Disorder (ADHD) under no drug, placebo and methylphenidate drug conditions. Findings from 26 studies were submitted to a meta-analytic procedure. In contrast to the contradictory findings of individual reports, our results revealed that children with ADHD made significantly more errors of omission and commission than normal children. As well, in children with ADHD and treated with methylphenidate, statistically significant reductions in the rate of both error types were noted. The effects of methylphenidate on the percentage of hits (i.e. 1 - omissions) were greater in experiments using shorter stimulus duration, smaller number of trials and higher probability of a target. Using Signal Detection Theory (SDT) parameters, we found that children with ADHD were less sensitive to the difference between targets and non-targets than their normal counterparts, while showing a comparable response bias. Similarly, the effects of methylphenidate were restricted to improving the sensitivity, while not affecting response bias, in both normal children and those with ADHD.

Does haloperidol block methylphenidate? Motivation or attention?

The effect of methylphenidate preceded by a moderate dose of haloperidol on reaction times over the duration of a continuous performance test (CPT), was investigated in ten male children, with a DSM-III diagnosis of attention deficit disorder with hyperactivity disorder (ADDH). Using a within-subject double-blind design, the effects of methylphenidate preceded by haloperidol on reaction time during the first and second blocks of CPT test were compared. Methylphenidate maintained a significantly improved reaction time in the second block of the CPT test. When methylphenidate, preceded by placebo, was preceded by haloperidol this effect was not observed, suggesting opposing effects on attentional systems by methylphenidate versus haloperidol. The study is the first to examine the "blocking" effect of haloperidol over the course of a CPT. The results suggest that dopamine systems are involved in the maintenance of the CPT response, and support an "incentive motivation" theory of sustained attention.

The effects of auditory stimulation on the arithmetic performance of children with ADHD and nondisabled children

This study evaluated the impact of extra-task stimulation on the academic task performance of children with attention-deficit/hyperactivity disorder (ADHD). Twenty boys with ADHD and 20 nondisabled boys worked on an arithmetic task during high stimulation (music), low stimulation (speech), and no stimulation (silence). The music "distractors" were individualized for each child, and the arithmetic problems were at each child's ability level. A significant Group x Condition interaction was found for number of correct answers. Specifically, the nondisabled youngsters performed similarly under all three auditory conditions. In contrast, the children with ADHD did significantly better under the music condition than speech or silence conditions. However, a significant Group x Order interaction indicated that arithmetic performance was enhanced only for those children with ADHD who received music as the first condition. The facilitative effects of salient auditory stimulation on the arithmetic performance of the children with ADHD provide some support for the underarousal/optimal stimulation theory of ADHD.

Sustained attention problems in children with early treated congenital hypothyroidism

Sustained attention was studied in 48 children with early treated congenital hypothyroidism and 35 healthy controls, using a computer-paced and a self-paced continuous performance task. The performance of the patients, particularly those in the low T4 group (38 patients with T4 levels < 50 nmol/l at neonatal screening), declined in the final stage of the computer-paced task, suggesting a problem in remaining attentive over time. The performance of all children declined in the first and improved in the final stage of the self-paced task. This pattern was most pronounced in the low T4 group, reflecting greater variability in their task performance over time, again indicating a problem in sustaining attention. No correlation was found between onset of treatment and sustained attention. The small size of the intermediate T4 group (10 patients with T4 levels > or = 50 nmol/l at neonatal screening) made the results more difficult to interpret and may have concealed a problem with sustained attention in this group.

Deficient inhibitory control in attention deficit hyperactivity disorder

The purpose of this study was to examine two executive control processes--response inhibition and re-engagement of responses after inhibition in children with attention deficit hyperactivity disorder (ADHD). Thirty-three children with ADHD and 22 normal control children of similar age (7 to 11 years) and mean IQ (107) were tested with the change paradigm. ADHD subgroups were defined by the context in which the ADHD symptoms predominated (in the home only; at school only; and in both, i.e., pervasive ADHD). Children with marked oppositional defiant or conduct disorder were excluded. Children with ADHD exhibited deficits in inhibitory control and in response re-engagement. Deficits were greatest in pervasive ADHD and, to a lesser extent, in those with ADHD limited to the school context. ADHD limited to the home context showed the least deficit. These results replicate an earlier study that found deficient inhibitory control in pervasive ADHD and demonstrate that the deficit in ADHD involves a second aspect of executive control.

Abnormal processing of irrelevant information in attention deficit hyperactivity disorder

The presence of a selective attention deficit in children with attention deficit hyperactivity disorder (ADHD) was investigated by administering a trial-by-trial version of the Stroop Color-Naming Task to children, aged 9-12, with ADHD (n = 19) and age-matched normal control children (n = 19). Performance was evaluated on both interference and facilitation components of the task. On the standard version of the task, with equal numbers of color words and neutral words, children with ADHD showed increased Stroop interference (prolongation of color-naming times by color-incongruent stimuli) but normal amounts of facilitation (speeding of color naming by color-congruent stimuli). This finding suggests that children with ADHD show increased disruption of color-naming performance by task-irrelevant information, probably secondary to decreased attentional control over the interference process. In contrast to findings of studies in adults, both groups of children failed to use an attentional strategy to reduce interference when they were administered blocks of trials that varied their expectancy for color word trials. This precluded a direct test of the diminished control hypothesis. There were no significant correlations between abnormal Stroop performance and impairment on the Continuous Performance Test or the Wisconsin Card Sorting Test or measures of IQ or reading performance. The implications of these findings for our understanding of information-processing deficits in children with ADHD and of the neurobiological underpinnings of these deficits are discussed.

Attentional difficulties in hyperactive and conduct-disordered children: a processing deficit

A random population sample of 1479 Chinese boys from Hong Kong was screened and diagnosed in a two-stage epidemiological study. Four groups, age 7-8, were distinguished: (1) a pure hyperactive group (HA), (2) a mixed hyperactive/conduct-disordered group (HA+CD), (3) a pure conduct-disordered group (CD), and (4) a normal control group (N). On a visual search task, only the HA children showed a specific processing deficit in performance. This confirms the diagnostic value of such a deficit for hyperactivity, differentiating it from conduct disorder. The failure to find a similar deficit in the HA+CD group raises questions concerning the clinical identity of these children. Each group showed a performance decrement over time in the visual search task but the decrement did not differ between the four groups. This observation is not congruent with the reports of a short attention span in hyperactive children; explanations of this apparent contradiction are considered.

Is the Continuous Performance Task a valuable research tool for use with children with Attention-Deficit-Hyperactivity Disorder?

The Continuous Performance Task (CPT) has become a popular research tool used to distinguish children with Attention-Deficit-Hyperactivity Disorder (ADHD) from their normal peers. Whether hyperactive children have a vigilance decrement remains an ongoing controversy. The theoretical basis of the CPT and variables known to influence performance are examined in order to interpret the inconsistencies evident in the research. Studies which employed the CPT in order to examine the possibility of sustained attention deficits in children with ADHD will be reviewed. The results are examined in light of group selection criteria, task variables and situational and external variables. It is concluded that there is no compelling evidence for a sustained deficit in ADHD children. An alternative theoretical model for understanding the results of CPT performance in ADHD children is provided.

Discriminant validity of attention-deficit hyperactivity disorder

OBJECTIVE

The primary purpose of this study was to assess the discriminant validity of attention-deficit hyperactivity disorder (ADHD) relative to well-defined groups of children with other psychiatric disorders.

METHOD

Clinic-referred patients diagnosed as having ADHD without any other comorbid diagnosis (N = 13), were compared with patients with only anxiety disorders (N = 20), disruptive disorders other than ADHD (N = 15), and nonreferred controls (N = 18) on measures of cognitive and academic functioning, as well as on objective measures of attention, impulse control, and activity level.

RESULTS

All three patient groups were found to have cognitive and academic achievement difficulties relative to controls. However, the ADHD group was found to be inattentive and impulsive relative to the other patient groups and the nonreferred controls. Objective measurement of activity level distinguished the ADHD group from controls but not from the other two patient groups.

CONCLUSIONS

These data support the diagnostic validity of a small subgroup of ADHD children (i.e., those without comorbid diagnoses) and demonstrates, that as a group, these children can be distinguished from patients with anxiety as well as other disruptive disorders on objective test measures.

Response perseveration, inhibitory control, and central dopaminergic activity in childhood behavior disorders

We screened students (N = 710) in grades four through six at two public elementary schools for behavior problems, using the Revised Behavior Problem Checklist. Five groups of children were identified: conduct disorder (n = 8), attention deficit disorder (n = 9), conduct disorder plus attention deficit disorder with hyperactivity (n = 11), anxiety-withdrawal (n = 12), and normal control (n = 15). A response perseveration task, inhibitory control task, and a noninvasive measure of dopaminergic activity were administered to selected students, and group differences were predicted based on Quay's hypotheses as derived from Gray's theory of brain function. Hypothesized group differences were not found, although analyses revealed dimensional relationships that were consistent with the hypotheses. Results are discussed in terms of Quay's hypotheses and potential modifications to tasks for future research.

A motor presetting study in hyperactive, learning disabled and control children

Motor presetting was investigated in hyperactive children, learning disabled children and normal controls. The reaction time of the hyperactive group was more sensitive to increases in interstimulus interval (event rate) than was that of the learning disabled and the controls. This finding indicates that hyperactive children have difficulty with motor presetting.

The effect of delay on hyperactive and non-hyperactive children's response times: a research note

Twenty-four hyperactive and 55 non-hyperactive children made a button press after the disappearance of a stimulus presented for either 1, 15 or 30 sec. Hyperactive children's responses were generally slower than those of non-hyperactive children and increased with length of pre-response delay, while non-hyperactive children's response time remained the same across all presentation levels. The results are interpreted as giving support to accounts that stress the role of pre-response delay, rather than time on task per se, as an important determinant of hyperactive children's attentional performance.

Specificity of inattention, impulsivity, and hyperactivity to the diagnosis of attention-deficit hyperactivity disorder

Children with attention-deficit hyperactivity disorder (ADHD) were compared with non-ADHD psychiatric patients and normal controls on objective measures of inattention, impulsivity, and hyperactivity to determine the specificity of these symptoms to ADHD. Inattention and impulsivity were assessed using a continuous performance test, and activity was measured using solid state actigraphs. Both patient groups were inattentive relative to normals, but were indistinguishable from each other. However, the ADHD group was more active than both non-ADHD patients and normals, who did not differ from each other. These data suggest that inattention may be a nonspecific symptom of child psychiatric disorder. However, ADHD may be uniquely characterized by overactivity.

The dimension of focussed attention: relationship to behavior and cognitive functioning in children

A sample of 73 nonreferred school children were administered a newly developed Visual Focussed-attention Test along with other measures of attentional, cognitive, and behavioral functioning. Internal reliability and construct validity for the test were established. Children were then divided into underfocussed (distractible, n = 6), normofocussed (n = 38), and overfocussed (n = 5) groups based upon their test scores. The three groups did not differ with regard to age, intellectual functioning, or academic achievement. However, the underfocussed and overfocussed groups contained a greater proportion of behaviorally disturbed children than the normofocussed group. Underfocussed children, as a group, were rated higher than normofocussed, but not higher than overfocussed children on the Hyperactivity factor of the Conners Teacher Questionnaire. The significance of these focussed attention deficits is reviewed in relation to the more familiar concepts of distractibility and hyperactivity.

The ecological validity of laboratory and analogue assessment methods of ADHD symptoms

An important question in the attempt to generalize laboratory findings on attention deficit-hyperactivity disorder (ADHD) children to clinical issues concerning their assessment, diagnosis, outcome, and treatment response is the ecological validity of the commonly used tasks and analogue behavioral observation procedures. This paper examines the concept of ecological validity and issues inherent in its evaluation. The evidence from a variety of sources is then reviewed on the relationship between laboratory methods of assessing inattention, impulsivity, and overactivity and measures of these same constructs in natural settings. Additional findings pertaining to this issue from a recent study of 140 ADHD and normal children and 159 ADHD and normal adolescents using a multimethod battery of tests are also reported. In general, the ecological validity of most methods is of a low to moderate degree, with some traditional laboratory tasks proving unsatisfactory. A few tasks demonstrated acceptable degrees of ecological validity but even these require improvement. It is concluded that future advances in ecological validity are likely to come from: (a) a greater reliance on assessments of the target behaviors in natural settings and (b) combining several of the more promising tasks and analogue methods into a battery that is taken over longer time intervals than has been customary and averaged across repeated administrations.

Reaction time indices of attention deficits in boys with disruptive behavior disorders

Boys with diagnoses in the disruptive behavior disorder (DBD) spectrum and normal controls were tested in two reaction time (RT) experiments. In Experiment I simple warned RT was measured and the length and regularity of the preparatory intervals were varied in order to study sustained attention in the sense of preparation. With age and IQ controlled, DBD boys had slower and more variable RT overall than controls and showed generally more pronounced effects of variations in the length and sequence of the preparatory intervals. The results suggest that DBD boys are subject to lapses of attention which are increased by a relatively long preparatory interval, and that they have a particular problem with temporal uncertainty. In Experiment II some aspects of selective attention were studied in a paradigm in which stimulus modality uncertainty and response selection were varied. DBD boys showed greater effects of modality uncertainty but not response selection than controls. No differences between subdiagnoses within the DBD spectrum could be demonstrated.

The specificity of the effects of stimulant medication on classroom learning-related measures of cognitive processing for attention deficit disorder children

There appear to be beneficial effects of stimulant medication on daily classroom measures of cognitive functioning for Attention Deficit Disorder (ADD) children, but the specificity and origin of such effects is unclear. Consistent with previous results, 0.3 mg/kg methylphenidate improved ADD children's performance on a classroom reading comprehension measure. Using the Posner letting-matching task and four additional measures of phonological processing, we attempted to isolate the effects of methylphenidate to parameter estimates of (a) selective attention, (b) the basic cognitive process of retrieving name codes from permanent memory, and (c) a constant term that represented nonspecific aspects of information processing. Responses to the letter-matching stimuli were faster and more accurate with medication compared to placebo. The improvement in performance was isolated to the parameter estimate that reflected nonspecific aspects of information processing. A lack of medication effect on the other measures of phonological processing supported the Posner task findings in indicating that methylphenidate appears to exert beneficial effects on academic processing through general rather than specific aspects of information processing.

Sustained attention and pervasive hyperactivity

A sustained attention deficit is defined as a significant decrement in task performance with task duration (time-on-task). Time-on-task effects are reported using a self-paced paper and pencil cancellation test (PPCT) in normals and in subgroups of pervasively hyperactive children. The hyperactive subgroups were pervasively hyperactive both at home and at school. They differed in degree of pervasiveness in three laboratory conditions. Task inefficiency was most pronounced in the most pervasively hyperactive group. There was no evidence in favour of a sustained attention deficit in hyperactivity: no differences were found in decline in task efficiency between the controls and the subgroups of hyperactive children.

Inattentive and noninattentive ADHD children: do they constitute a unitary group?

Teacher-rated ADHD and normal control children were administered a continuous performance test (CPT), and were then further subdivided based upon the presence or absence of objectively assessed attentional deficits. In addition, children were assessed using several measures of cognitive and behavioral functioning. Attentional deficits were significantly more prevalent among the ADHD group, but about half of the ADHD children showed no evidence of objectively assessed attentional dysfunction. Further group analyses indicated that ADHD children with objectively assessed attentional dysfunction appeared cognitively impaired, while ADHD children without objective evidence of attentional dysfunction had more conduct problems. CPT inattention was not related to the presence of cognitive impairments or conduct problems in the control group. These data must be considered preliminary because teacher ratings were the only source of diagnosis and a single measure of inattention was used. However, they suggest that two subtypes of ADHD children can be identified, one characterized by inattention and learning problems, and the other by conduct problems.

Additive factor method applied to psychopathology with special reference to childhood hyperactivity

A review is made of available studies using the Additive Factor Method (AFM) in clinical research. The paper argues that by using the AFM in studies of psychological dysfunctioning a major contribution can be made: first, in preventing spurious findings, second, distinguishing between group differences with and without information processing deficits, and third, by identifying fundamental processes which may be impaired. This may offer psychodiagnostics an empirical basis on which to define disorders. This paper reviews studies contributing to this endeavour. It further raises the question of how to interpret clinical research, which is conducted in the tradition of information processing but not within the frame of reference of the AFM. It is suggested that such research is useful and complementary to that conducted using the AFM. Further, it is suggested that the role of energetical factors in clinical disorders and in their treatment is an important area for future experimental clinical research.

Reaction time, impulsivity, and attention in hyperactive children and controls: a video game technique

Maturation of sustained attention was studied in a group of 52 hyperactive elementary school children and 152 controls using a microcomputer-based test formatted to resemble a video game. In nonhyperactive children, both simple and complex reaction time decreased with age, as did variability of response time. Omission errors were extremely infrequent on simple reaction time and decreased with age on the more complex tasks. Commission errors had an inconsistent relationship with age. Hyperactive children were slower, more variable, and made more errors on all segments of the game than did controls. Both motor speed and calculated mental speed were slower in hyperactive children, with greater discrepancy for responses directed to the nondominant hand, suggesting that a selective right hemisphere deficit may be present in hyperactives. A summary score (number of individual game scores above the 95th percentile) of 4 or more detected 60% of hyperactive subjects with a false positive rate of 5%. Agreement with the Matching Familiar Figures Test was 75% in the hyperactive group.

Evidence of difficulties in sustained attention in children with ADDH

It has been suggested that children with ADDH have specific difficulties in sustained attention. Despite some early studies supporting this position, many recent reports using continuous performance tests (CPTs) have failed to confirm this hypothesis. Possible reasons for this discrepancy are outlined and an attempt to corroborate and extend an earlier study (Sykes, Douglas, & Morgenstern, 1973) was undertaken. CPT results in normal children indicated that changes in performance over time, although not affected by gender, were influenced by age. Data from ADDH subjects indicated that they performed significantly more poorly with time on task than did controls. These results suggest that the ability to sustain attention increases with age and does not vary by gender. Furthermore, difficultues in the ability to sustain attention can be demonstrated in children with ADDH. Finally, it is suggested that within-age-level comparisons between groups of ADDH and controls would be more clinically sensitive than across-age-group comparisons.

The additive factor method: a differential diagnostic tool in hyperactivity and learning disability

The Additive Factor Method assumes that task performance is the sum of sequential and independent processes. We studied the duration of the central processes (memory search and decision) and the motor decision process in hyperactive and learning-disabled children under so-called divided attention and S-R compatibility conditions. It was found that the learning-disabled were impaired in memory search and decision processes whereas hyperactives were impaired in the motor decision process.