Adult ADHD. Analysis of self-ratings on a behavior questionnaire.

It is customary to acquire behavior ratings of children with ADHD from parents and teachers, but comparable informants are typically not available for adults. Self-rating is substituted. The present study presents self-ratings of ADHD and control adults on a 43-item scale. The groups differed significantly on all but 4 descriptors, and 3 sufficed to account for more than 50% of the variance, reflecting distractibility, impulsivity and lack of control of behavior, respectively. Discriminant analysis revealed 83% and 90% correct classification of ADHD and controls, respectively. The results support the usefulness of self-rating in adults with ADHD and corroborate the resemblance and continuity between childhood and adult ADHD.

Adult ADHD. Controlled medication assessment.

Many adults with ADHD respond to stimulant therapy, but controlled medication assessments have not been reported. We administered an effortful working memory task in four half-day sessions, double blind, at methylphenidate levels of 0, 5, 10 and 20 mg. Dose-response curves were established individually. Fifteen of 17 patients displayed a favorable response to one or more levels of medication; that is, they achieved more correct responses and less variability than on placebo. Each dose level elicited optimal performance from some of the patients. Unlike monitoring by self-report, the objective medication assessment offers an expeditious approximation to the ultimate optimal dose, potentially saving the patient weeks on an ineffective and/or excessive dosage regime.

Time estimation by patients with frontal lesions and by Korsakoff amnesics.

We studied time estimation in patients with frontal damage (F) and alcoholic Korsakoff (K) patients in order to differentiate between the contributions of working memory and episodic memory to temporal cognition. In Experiment 1, F and K patients estimated time intervals between 10 and 120 s less accurately than matched normal and alcoholic control subjects. F patients were less accurate than K patients at short (< 1 min) time intervals whereas K patients increasingly underestimated durations as intervals grew longer. F patients overestimated short intervals in inverse proportion to their performance on the Wisconsin Card Sorting Test. As intervals grew longer, overestimation yielded to underestimation for F patients. Experiment 2 involved time estimation while counting at a subjective 1/s rate. F patients' subjective tempo, though relatively rapid, did not fully explain their overestimation of short intervals. In Experiment 3, participants produced predetermined time intervals by depressing a mouse key. K patients underproduced longer intervals. F patients produced comparably to normal participants, but were extremely variable. Findings suggest that both working memory and episodic memory play an individual role in temporal cognition. Turnover within a short-term working memory buffer provides a metric for temporal decisions. The depleted working memory that typically attends frontal dysfunction may result in quicker turnover, and this may inflate subjective duration. On the other hand, temporal estimation beyond 30 s requires episodic remembering, and this puts K patients at a disadvantage.

Allocation of attention in dichotic listening: effects on the detection and localization of targets within lists.

In each of two dichotic listening experiments, 48 normal right-handed adults were instructed to attend selectively to the left and right ears and to divide attention equally between ears. Participants listened for specified targets and reported the ear of entry when the target was heard. Stimuli consisted of lists of digit names in Experiment I and lists of words in Experiment 2. Shifts of attention altered ear asymmetry for localizing but not for detecting digit names. For words, attention shifts altered both detection asymmetry and localization asymmetry, but the effect of attention on detection seemed to reflect differential retrieval from short-term memory rather than differential perception. In both experiments, shifting attention toward either ear resulted in a reporting bias such that signals were attributed to the attended ear more often than to the unattended ear. The results confirm our previous findings, for single pairs of stimuli, that volitional shifts of attention alter response selection rather than perception.

Allocation of attention in dichotic listening: differential effects on the detection and localization of signals.

In 2 dichotic listening experiments, 96 normal right-handed adults attended selectively to the left and right ear and divided their attention equally between both ears. Participants listened for specified targets and reported the ear of entry. The material consisted of pairs of consonant-vowel syllables in Experiment 1 and pairs of rhyming consonant-vowel-consonant words in Experiment 2. Both experiments yielded a right-ear advantage for detection and for localization. Attention instructions had no effect on detection. However, focusing attention on 1 ear increased the number of targets attributed to that ear while decreasing the number of targets attributed to the opposite ear. The dissociation between detection and localization indicates that volitional shifts of attention influence late (response selection) processes rather than early (stimulus identification) processes. Selective-listening effects can be accounted for by a 2-stage model in which a fixed input asymmetry is modulated by a biased selection of responses.

Effects of left-sided movements on line bisection in unilateral neglect.

Thirteen patients with left neglect performed line bisection under four conditions: no cue, visual cueing involving the report of a digit placed at the left end of the line, circling the left-end digit, and digit circling plus tracing of the line with the right index finger from its left end to its midpoint before bisection. Digit circling plus finger tracing was unequivocally more effective in reducing left neglect than digit circling alone, which was in turn more effective than visual cueing; indeed, digit circling with tracing completely abolished the rightward bisection bias. Thus continuously directing visuomotor control to the left side of the line (even with the right hand) until bisection is performed reduces neglect more than only requiring patients to attend to left-sided visual cues. The facilitatory effects of the cueing procedures may reflect their differential efficacy in constraining as well as attracting attention and action to the left part of the target line. These findings have implications for neglect rehabilitation.

Divergent thinking styles of the hemispheres: how syllogisms are solved during transitory hemisphere suppression.

Psychiatric patients solved syllogisms while recovering from transitory ictal suppression of one hemisphere by electroconvulsive therapy (ECT). The premises were familiar or unfamiliar, true or false. While the right hemisphere was suppressed, syllogisms were usually solved by theoretical, deductive reasoning even when the factual answer was known a priori, the premises were obviously false and the conclusions were absurd. While their left hemisphere was suppressed, the same subjects applied their prior knowledge; if the syllogism content was unfamiliar or false, they refused to answer. We postulate a left-hemisphere mechanism capable of decontextualized mental operations and a right-hemisphere mechanism, the operation of which is context-bound and incapable of abstraction. We show that each hemisphere tends to overextend its perspective on the problem and that in the intact brain they both contribute to an extent that depends on the characteristics of the problem at hand.

Shifts in children's ear asymmetry during verbal and nonverbal auditory-visual association tasks: a "virtual stimulus" effect.

Dichotic consonant-vowel-consonant (CVC) syllables were presented to 96 right-handed children between the ages of 8 and 12 years. Children were assigned either to a "code" condition that entailed translating the CVCs into English words or to a "bird" condition in which the CVCs had to be matched to cartoons of birds. A differential ear asymmetry for the code and bird tasks developed linearly across four blocks of trials. By Block 4, the code task yielded a significant right-ear advantage and the bird task yielded no ear advantage. The results are inconsistent with any model that attributes ear asymmetries entirely to fixed structural characteristics of the nervous system. Instead, ear asymmetries are influenced by the subject's categorization of the stimuli, i.e., by "virtual stimuli". These appear to be constructed over time (blocks of trials).

Functional significance of individual variations in callosal area.

We considered the hypothesis that the richness of callosal interhemispheric connections has a role in determining the degree of behavioural laterality and time-sharing ability in dual-task performance. Behavioural laterality as measured by dichotic word listening, line bisection and turning bias tests correlated inversely with the midsagittal cross-sectional area of the corpus callosum, as seen on MRI. The amount of dual task interference was strongly inversely correlated with the callosal area in both within-hemisphere and between-hemispheres conditions. These relationships between normal variations in callosal area, and outcomes on tests both of laterally and time-sharing capacity in normal adults suggest that the corpus callosum assumes a cross-excitatory role when subjects perform these tasks.

Progress in the measurement of laterality and implications for dyslexia research.

Much of contemporary laterality research has been motivated by a need to increase the accuracy with which individuals can be classified as left- or right-hemisphere dominant for speech and language. Efforts to improve the classification accuracy of laterality methods have led not only to the refinement of laterality methods but also to the discovery of some of the mechanisms that contribute to asymmetric performance. Despite these advances, laterality methods still do not lead to definitive conclusions about hemispheric specialization in the individual case, and special caution must be used when interpreting results for individual dyslexic children. Event-related measurements of cerebral metabolism, still in the development phase, promise to complement but not replace behavioral laterality methods.

Attention deficit disorder in children: three clinical variants.

A clinic-referred population of 116 children with attentional problems was classified by DSM-III [attention deficit disorder (ADD)] with respect to inattention, impulsivity, and hyperactivity. The sample proved to subdivide into three groups: inattentive, impulsive, and hyperactive (HII), n = 60; inattentive and impulsive (II), n = 26; and inattentive (I), n = 30. The distinction between II and I resolves the confounding of impulsivity and inattention in previous studies of children who have ADD but are not hyperactive. The three groups were found to be similar in mean age, gender ratio, prevalence, and pattern of associated learning disabilities, family history of psychopathology, and probability of favorable response to methylphenidate. Group I differed from Groups HII and II in the frequency of externalizing relative to internalizing comorbid psychopathology. A group that is hyperactive and impulsive but not inattentive was not found. The preponderance of similarities in associated characteristics suggests that the three groups are differing clinical presentations of an ADD spectrum.

Are families of children with reading difficulties at risk for immune disorders and nonrighthandedness?

This study used questionnaire data to examine immune disorders and nonrighthandedness in the families of children enrolled in a learning disabilities school and children attending regular classrooms in public schools. Groups were organized according to their performance on a standardized test of reading comprehension to avoid overlap. In total, 468 questionnaires were returned, from which we were able to derive a final sample of carefully matched subjects: 55 subjects undergoing remediation for reading problems and 55 age- and sex-matched control subjects. The results indicated that children with reading problems and their families more frequently suffered from some immune and autoimmune disorders, particularly those involving the gastrointestinal tract and the thyroid gland. In addition, symptoms of attention deficit hyperactivity disorder were associated with Crohn's disease and migraine headache in the families. There was no evidence of an elevated prevalence of nonrighthandedness in the children with reading problems and their families.

Integrated cortical field model of consciousness.

The idea that there is a localized module or limited capacity mechanism in the brain that subserves consciousness is wrong. Awareness is a product of the activity of widely distributed neuronal assemblies that represent diverse aspects of experience. Central to a representation's entry into consciousness is its integration into the currently dominant pattern of central neuronal activity (dominant focus). A representation anywhere in the forebrain could on one occasion enter consciousness and on another remain outside it, depending on whether it is, perhaps by temporal coherence of discharge of cell assemblies, integrated into the dominant focus. There is no privileged locus or 'internal eye' for the benefit of which input is elaborated and toward which information must be transported. When a perceptual decision is made there need be no re-enactment ('filling in') of the appearance in question. Nor is there a 'finish line', the crossing of which determines the perceived sequence of events. Neuropsychological syndromes that involve unawareness of a perceptual domain illustrate the explanatory value of this integrated cortical field model of consciousness. Awareness cannot be conceptualized as separate from the neural activity of which it is the subjective concomitant. Being aware is what it is like to have a particular pattern of neuronal activity. To regard consciousness as arising from brain activity by some esoteric transformation is misconceived.

The effects of parental immunoreactivity on pregnancy, birth, and cognitive development: maternal immune attack on the fetus?

The effects of parental immunoreactivity were tested in two ways on questionnaire data collected from 468 children and their families. (1) It was found that the presence of learning difficulties in boys was associated with pregnancy and birth complications, as well as with maternal immunoreactivity. Paternal immunoreactivity did not appear to be related to any of the variables in question. (2) The antecedent brother effect, that children, particularly males, with older brothers have higher rates of the same set of variables, was not found. Maternal immunoreactivity emerges as a risk factor for pregnancy, birth, and cognitive development, but not exclusively by the proposed mechanism of maternal immune attack on the fetus.