An electrophysiological study of school-aged children with a history of failure to thrive during infancy.

Sixty-five subjects, ages 8 to 12, participated in a visual electrophysiological study. Twenty-two of the subjects had received a diagnosis of nonorganic failure-to-thrive (FTT) before the age of three. The remaining 43 subjects had no history of FTT and served as Controls. IQs were obtained with the abbreviated WISC-III, and the Controls were split into two groups, LO IQ and HI IQ, to provide a LO IQ Control group with an average IQ equivalent to the FTT group. Event-related brain potentials (ERPs) were recorded from five scalp locations during a cued continuous performance task (CPT). Subjects had to press a button every time they saw the letter "X" following the letter "A" (50 targets out of 400 stimuli). During the CPT, the FTT subjects made marginally more errors of omission to targets than the LO IQ Control group and significantly more errors of omission than the HI IQ Control subjects. The groups did not differ significantly on errors of commission (false alarms) or reaction times to targets. ERP averages revealed a group difference in amplitude in a late slow wave for the 50 non-X stimuli (false targets) that followed the letter A. This difference was greatest over frontal sites, where the FTT group had a more negative going slow wave than each control group. Late frontal negativity to No Go stimuli has been linked with post-decisional processing, notably in young children. Thus, the FTT subjects may have less efficient inhibitory processes, reflected by additional late frontal activation.     

Training letter discrimination in four-year-old children

Four-year-old children were tested on letter discrimination. Subjects in two experimental groups went through an experimental training program on a match-to-sample apparatus. Subjects in the experimental-critical group were given reinforcers for responding to features of the stimuli thought critical for discriminating letters while subjects in the experimental-noncritical group were given reinforcers for responding to non-critical features. Subjects went through the training program daily until they reached criterion; then they were posttested on letters. Subjects in a control group received no training but were posttested. Subjects in all groups made fewer errors on the posttest. Subjects in the experimental-critical group made significantly fewer posttest errors than subjects in the experimental-noncritical group, lending support to the hypothesis that reinforcement of discriminative responding to critical features of letter-like stimuli results in greater improvement in letter discrimination than reinforcement of discriminative responding to noncritical features of stimuli. Analysis of confusion matrices provided tentative indications of the nature of letter confusions in 4-yr-old children.     

Relations Between Continuous Performance Test Performance Measures and ADHD Behaviors

The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly been shown to differentiate ADHD from normal groups. Several variables may be derived from the Conners' CPT including errors of omission and commission, mean hit reaction time(RT), mean hit RT standard error, d', and . What each CPT parameter actually assesses has largely been based upon clinical assumptions and the face validity of each measure (e.g., omission errors measure inattention, commission errors measure impulsivity). This study attempts to examine relations between various CPT variables and phenotypic behaviors so as to better understand the various CPT variables. An epidemiological sample of 817 children was administered the Conners' CPT. Diagnostic interviews were conducted with parents to determine ADHD symptom profiles for all children. Children diagnosed with ADHD had more variable RTs, made more errors of commission and omission, and demonstrated poorer perceptual sensitivity than nondiagnosed children. Regarding specific symptoms, generalized estimating equations (GEE) and ANCOVAs were conducted to determine specific relationships between the 18 DSM-IV ADHD symptoms and 6 CPT parameters. CPT performance measures demonstrated significant relationships to ADHD symptoms but did not demonstrate symptom domain specificity according to a priori assumptions. Overall performance on the two signal detection measures, d' and , was highly related to all ADHD symptoms across symptom domains. Further, increased variability in RTs over time was related to most ADHD symptoms. Finally, it appears that at least 1 CPT variable, mean hit RT, is minimally related to ADHD symptoms as a whole, but does demonstrate some specificity in its link with symptoms of hyperactivity.     

A controlled clinical comparison of attention performance in children with ADHD in a virtual reality classroom compared to standard neuropsychological methods.

In this initial pilot study, a controlled clinical comparison was made of attention perforance in children with attention deficit-hyperactivity disorder (ADHD) in a virtual reality (VR) classroom. Ten boys diagnosed with ADHD and ten normal control boys participated in the study. Groups did not significantly differ in mean age, grade level, ethnicity, or handedness. No participants reported simulator sickness following VR exposure. Children with ADHD exhibited more omission errors, commission errors, and overall body movement than normal control children in the VR classroom. Children with ADHD were more impacted by distraction in the VR classroom. VR classroom measures were correlated with traditional ADHD assessment tools and the flatscreen CPT. Of note, the small sample size incorporated in each group and higher WISC-III scores of normal controls might have some bearing on the overall interpretation of results. These data suggested that the Virtual Classroom had good potential for controlled performance assessment within an ecologically valid environment and appeared to parse out significant effects due to the presence of distraction stimuli.     

Frontal and striatal brain lesions increase susceptibility to masking in perceptual decisions

Recent data suggest that perceptual decisions on masked stimuli involve neural activity in frontal cortex. We examined the effect of damage to frontal and striatal brain regions in man on the susceptibility to backward masking in rapid stimulus streams. Patients with unilateral frontal excisions and patients with early Huntington's disease were compared to controls in the identification of a brief white letter embedded in short streams of black letters at two presentation rates: (a) 9 letters/s; (b) 12.5 letters/s and also in a control condition in which the first post-target masking letter was absent. Patients could identify the target when the post-target mask was absent, but reducing the delay between stimuli significantly increased the error rates in patients. Intrusion errors often involved reporting post-target or pre-target distractors instead of the target. These results suggest that fronto-striatal lesions increase the period during which perceptual decisions are susceptible to perturbation. This deficit is compatible with a functional role of frontal systems in the cognitive control of brief perceptual decisions.     

Learning-disordered children's evoked potentials during sustained attention

Evoked potentials and performance of 19 learning-disordered (LD) and 19 normally achieving children were studied in two versions of the Continuous Performance Test (CPT). In both CPT procedures, LD children made more errors of omission and commission than did normal children. Evoked potential differences between groups were especially prominent in the more difficult BX version of the CPT. LD children displayed significantly smaller late positive components (LPC) of the evoked potential to critical stimuli in the task. There were no LPC differences between diagnostic groups for noncritical stimulus categories. The results suggest a deficit in behavioral and cortical indices of sustained attention among LD children.This research is based on a doctoral dissertation in psychology submitted by the first author (Dainer, 1980) and supervised by the second author. The research was partly supported by NIMH Grant MH 32103 and New York State Health Research Council Contract 1396 to the second author. We are grateful to the Strong Memorial Hospital Learning Disorders Clinic; B.O.C.E.S. School #1, Fairport, New York; Rochester Learning Disabilities Association; and Winifred Stebbins for referring learning-disordered children, and to the Rochester Central YMCA for referring normally achieving children. The University of Rochester College of Arts and Science provided partial support for computer funds. For their assistance, we are grateful to Lance Bauer, John Chapman, Michael Davidson, Dale McAdam, James Metz, and Lawrence Ota.     

Incidental learning,distraction, and sustained attention in hyperactive and control subjects

Thirty-two children designated as hyperactive (ADD) were compared with an equal number of control subjects who were matched for age, sex, and verbal IQ. The subjects were tested on (1) a component selection task, measuring serial memory and incidental learning and (2) a cancellation task, assessing attentional variables and distractibility. No straightforward group differences were found on the component selection task, whereas hyperactive subjects made more omission and commission errors than controls on the cancellation task. It was concluded that a deficit in sustained attention and impulsivity best described the group differences. Age was also found to influence performance on a number of variables, including incidental learning on the component selection task and response rate and omission errors on the cancellation task. Because subjects in the hyperactive group were rated as extreme on a number of subscales not necessarily related to hyperactivity, the data were reexamined by multiple regression analyses. Subscales considered to be related both to hyperactivity and to conduct disorder were associated with different performance variables, indicating that each of these subscales provided some unique information.This study was supported by a grant from the Medical Research Council of New Zeland to the first author. The authors would like to thank the pupils and staff of Mt. Eden Normal Primary School and Newmarket School for taking part in the study, and the Auckland Education Board for granting approval for the study. We also thank Prof. J. S. Werry, Dr. J. Reeves, and Mrs. G. Elkind for assistance in locating some of the control subjects. Special thanks goes to Gail Elkind for assistance with the statistical analysis.     

When do letter features migrate? A boundary condition for feature-integration theory

Feature-integration theory postulates that a lapse of attention will allow letter features to change position and to recombine as illusory conjunctions (Treisman & Paterson, 1984). To study such errors, we used a set of uppercase letters known to yield illusory conjunctions in each of three tasks. The first, a bar-probe task, showed whole-character mislocations but not errors based on feature migration and recombination. The second, a two-alternative forced-choice detection task, allowed subjects to focus on the presence or absence of subletter features and showed illusory conjunctions based on feature migration and recombination. The third was also a two-alternative forced-choice detection task, but we manipulated the subjects' knowledge of the shape of the stimuli: In the case-certain condition, the stimuli were always in uppercase, but in the case-uncertain condition, the stimuli could appear in either upper- or lowercase. Subjects in the case-certain condition produced illusory conjunctions based on feature recombination, whereas subjects in the case-uncertain condition did not. The results suggest that when subjects can view the stimuli as feature groups, letter features regroup as illusory conjunctions; when subjects encode the stimuli as letters, whole items may be mislocated, but subletter features are not. Thus, illusory conjunctions reflect the subject's processing strategy, rather than the architecture of the visual system.     

Frontal lobe functions in attention deficit disorder with and without hyperactivity: A review and research report

We review 22 neuropsychological studies of frontal lobe functions in children with attention deficit disorder with and without hyperactivity (ADD/+H,ADD/-H). Some measures presumed to assess frontal lobe dysfunctions were not reliably sensitive to the deficits occurring in either form of ADD. Tests of response inhibition more reliably distinguished ADD/+H from normal children. Where impairments were found on other tests between ADD and normal subjects, they were highly inconsistent across studies and seemed strongly related to age of the subjects and possibly to the version of the test employed. Other methodological differences across studies further contributed to the discrepant reports. The co-morbidity of other disorders, such as learning disabilities (LD) and conduct problems, with ADD may be an additional confounding factor in some, though not all, of these studies. In a separate study, children with ADD/+H (n=12) were then compared on frontal lobe tests to three other groups: ADD/-H (n=12), LD but no ADD (n=11),and normal children (n=12) statistically covarying for differences in conduct problems across groups. Most measures did not distinguish among these groups. Both ADD groups made more omission errors on a Continuous Performance Test (CPT) than the normal group. All three clinical groups performed more poorly on the word and interference portions of the Stroop Test. Thus, while both types of ADD share some apparent similarities in deficits on a few frontal lobe tests in this study, the totality of existing findings suggests an additional problem with perceptual-motor speed and processing in the ADD/-H group.This research was supported by NIMH grant MH41464 and by funds from the Department of Psychiatry, University of Massachusetts Medical Center. The authors are grateful to Judy Tessier and Ellen Mintz-Lennick for their assistance with some of the data collection and scoring. The comments of Virginia Douglas on an earlier draft of this paper are greatly appreciated.     

Processing letters in words at different levels

Subjects indicated whether two letters, two words, or a letter and the first letter of a word were the same. Letter targets were matched more quickly than word targets when the stimuli were presented simultaneously. When the target and comparison stimuli were separated by a 3-sec interval, word targets were matched more quickly than a letter and a letter in a word. It was also shown that the physical similarity of the targets and comparison stimuli had a greater effect in the simultaneous matching conditions. These findings are consistent with a model of word processing in which letters are individually compared prior to word identification at a physical level of processing. At a higher level of processing, words may be encoded as a unit, and the identification of the letters within the word may require a decoding of the word unit.     

Probability effects on stimulus evaluation and response processes.

This study investigated the effects of probability information on response preparation and stimulus evaluation. Eight subjects responded with one hand to the target letter H and with the other to the target letter S. The target letter was surrounded by noise letters that were either the same as or different from the target letter. In 2 conditions, the targets were preceded by a warning stimulus unrelated to the target letter. In 2 other conditions, a warning letter predicted that the same letter or the opposite letter would appear as the imperative stimulus with .80 probability. Correct reaction times were faster and error rates were lower when imperative stimuli confirmed the predictions of the warning stimulus. Probability information affected (a) the preparation of motor responses during the foreperiod, (b) the development of expectancies for a particular target letter, and (c) a process sensitive to the identities of letter stimuli but not to their locations.     

The effect of methylphenidate on very low frequency electroencephalography oscillations in adult ADHD

Altered very low-frequency electroencephalographic (VLF-EEG) activity is an endophenotype of ADHD in children and adolescents. We investigated VLF-EEG case-control differences in adult samples and the effects of methylphenidate (MPH). A longitudinal case-control study was conducted examining the effects of MPH on VLF-EEG (.02–0.2 Hz) during a cued continuous performance task. 41 untreated adults with ADHD and 47 controls were assessed, and 21 cases followed up after MPH treatment, with a similar follow-up for 38 controls (mean follow-up = 9.4 months). Cases had enhanced frontal and parietal VLF-EEG and increased omission errors. In the whole sample, increased parietal VLF-EEG correlated with increased omission errors. After controlling for subthreshold comorbid symptoms, VLF-EEG case-control differences and treatment effects remained. Post-treatment, a time by group interaction emerged; VLF-EEG and omission errors reduced to the same level as controls, with decreased inattentive symptoms in cases. Reduced VLF-EEG following MPH treatment provides preliminary evidence that changes in VLF-EEG may relate to MPH treatment effects on ADHD symptoms; and that VLF-EEG may be an intermediate phenotype of ADHD. Further studies of the treatment effect of MPH in larger controlled studies are required to formally evaluate any causal link between MPH, VLF-EEG and ADHD symptoms.     

Words fail: Lesion-symptom mapping of errors of omission in post-stroke aphasia

Impaired object naming is a core deficit in post-stroke aphasia, which can manifest as errors of commission – producing an incorrect word or a non-word – or as errors of omission – failing to attempt to name the object. Detailed behavioural, computational, and neurological investigations of errors of commission have played a key role in the development of neurocognitive models of word production. In contrast, the neurocognitive basis of omission errors is radically underspecified despite being a prevalent phenomenon in aphasia and other populations. The prevalence of omission errors makes their neurocognitive basis important for characterizing an individual's deficits and, ideally, for personalizing treatment and evaluating treatment outcomes. This study leveraged established relationships between lesion location and errors of commission to investigate omission errors in picture naming. Omission error rates from the Philadelphia Naming Test for 123 individuals with post-stroke aphasia were analysed using support vector regression lesion-symptom mapping. Omission errors were most strongly associated with left frontal and mid-anterior temporal lobe lesions. Computational model analysis further showed that omission errors were positively associated with impaired semantically driven lexical retrieval rather than phonological retrieval. These results suggest that errors of omission in aphasia predominantly arise from lexical–semantic deficits in word retrieval and selection from a competitor set.     

Impulsivity and control of inhibition in Benign Focal Childhood Epilepsy (BFCE)

Childhood epilepsy represents abnormal brain functioning and may affect cognitive functions that depend on the late development of the frontal lobes. This study addresses the possible consequences of benign epilepsy on frontal functions, specifically action regulation and inhibition in the absence of explicit frontal neurological signs. Thirteen children (8 males; 6-12 years old) with benign epilepsy were matched to 13 controls. They performed tasks designed to measure impulsivity and control of inhibition: CPT, Stop Signal Paradigm, Stroop test, and Matching Familiar Figures Test (MFFT). Children with epilepsy made more errors on the MFFT (p < .02), made more errors in the interference condition on the Stroop test (p < .01), and had a longer response time to the Stop Signal (p < .05) than controls, with no differences on nonexecutive functions measures. Thus, children with benign epilepsy have a deficit on some measures of impulsivity and inhibition, which may reflect poor frontal lobe functioning.     

Processes underlying dimensional interactions: Correspondences between linguistic and nonlinguistic dimensions

In six experiments, we examined speeded classification when one dimension was linguistic and the other was nonlinguistic. In five of these, attributes on the dimensions corresponded meaningfully, having in common the concepts "high" and "low." For example, in Experiment 1, the visually presented words HI and LO were paired with high- or low-pitched tones; in Experiment 2, the dimensions were visual words and vertical position, in Experiment 3, they were spoken words and position, and in Experiments 4 and 5, spoken words and pitch. For each dimension in each pair, subjects suffered Garner interference when dimensions were varied orthogonally. Garner interference remained constant across 15 blocks of trials (Experiment 5). Subjects also showed significant congruity effects in all experiments, with attributes from congruent stimuli (e.g., HI/high pitch) classified faster than attributes from incongruent stimuli (e.g., HI/low pitch). These results differ from those obtained previously with noncorresponding pairs of linguistic-nonlinguistic dimensions. The results also differ from those obtained with traditional Stroop dimensions (colors and color words; Experiment 6), which showed minimal Garner interference and diminishing congruity effects across blocks of trials. We conclude that the interactions found here represent cross-talk between channels within a semantic level of processing. We contrast our view with current models of dimensional interaction.     

Effects of Grammatical Categories on Letter Detection in Continuous Text

The present study focuses on the interplay between the linguistic principles and the psycholinguistic processes involved in reading. Results from 56 participants on a letter detection task reveal that readers do not process all function words in the same manner. Omission rates were highest for function words occupying the head of maximal projections such as complementizers and determiners. Prepositions were shown to occupy an intermediary position between content and function words, with omission rates varying depending on their semantic load. Together these results appear to bolster and offer a finer grained picture of the role of function words within the framework of both the Guidance Organization (Greenberg et al. in Psychon Bull Rev 11(3):428–433, 2004) and Attentional Disengagement (Roy-Charland et al. in Percept Psychophys 69(3):324–337, 2007) reading models. The results of the present study are discussed using an X-bar theory approach with the goal of refining the structural account of letter detection errors.     

Decisions concerning the rejected channel

It was thought that the physical aspects of auditory stimuli were possibly transmitted via separate pathways from those transmitting the verbal aspects. Three experiments were designed to test this hypothesis. In these experiments subjects had to perform a shadowing task and had to respond simultaneously on response keys to pips superimposed in either ear on verbal messages. The response to these pips was of increasing complexity, in that it was a simple reaction time which was measured in the first experiment, a choice reaction time in the second experiment and a more complex choice reaction time in the third experiment. Subjects were able to perform these tests although the increasing difficulty was reflected in longer reaction times and more errors. The reaction times to the pips presented to the ear which was not being shadowed were slower, and the errors, made to pips in both channels, were “false positives” rather than errors of omission. These results were taken as favouring the hypothesis.     

Continuous Performance Test Performance in a Normative Epidemiological Sample

A 14-min continuous performance test (CPT) requiring a high rate of responding was administered to a probability-weighted random sample of 816 9–17-year-old children drawn from a population of 17,117 children in an ongoing epidemiological and longitudinal study in Western North Carolina. Systematic main effects of improved performance with older age were found in this age range for all variables, including reaction time (RT), RT standard error, errors of omission, errors of commission, and signal detection parameters (d' and ). Significant gender main effects included more impulsive errors, less variability, and faster RT by males, with no interactions between age and gender. There were no main effects of ethnicity or interactions of ethnicity with age and/or gender. Large main effects of interstimulus interval (ISI; 1, 2, or 4-s intervals) and time block were present for most CPT performance measures. The normative data from the CPT should provide a useful framework for interpreting similar data in future studies of child and adolescent psychopathology.