Gert Camfferman

Auditory event-related brain potentials in autistic children and three different control groups

ERPs to auditory stimuli, generated during an oddball task, were obtained in a group of autistic children and three control groups (normal, ADDH, and dyslectic children, respectively). The task included the presentation of standards, deviants, and novels and had a (between-group) passive vs. active (counting) condition. It was examined whether 1) it was possible to replicate several earlier findings, 2) autistics manifest an abnormal lateralization pattern of ERPs, 3) autistics have an abnormal mismatch negativity (MMN), and 4) differences between autistics and normals are really specific to the autistic group. The only finding that could be replicated was that autistics have a smaller A/Pcz/300. There was no evidence for abnormal lateralization or abnormal MMN; however, there was an unexpected effect of the task manipulation on the amplitude of the P3: in autistics, the occipital P3 to deviant stimuli was significantly larger in the active than in the passive condition, a finding, like the replication of the smaller A/Pcz/300, specific to the autistic group. It was suggested that the auditory occipital task effect is related to understimulation of the occipital lobe by visual stimuli in autistic children.

Event-related potentials and performance of attention-deficit hyperactivity disorder: Children and normal controls in auditory and visual selective attention tasks

Attention-deficit hyperactivity disorder (ADHD) children and normal controls (7-13 yrs old) performed an auditory and visual selective attention task. Subjects were instructed to respond to the infrequent (10%) stimuli in the relevant channel. Processing negativity (PN) and several other ERP peaks were scored at the midline electrodes. In the auditory task, controls had more correct detections (hits), less false alarms, larger P3b amplitudes to nontarget stimuli (but not to hits), a larger central PN and larger early frontal positivity (100-250 ms) to target stimuli than ADHD subjects. In the visual modality, controls had more correct detections, less false alarms, larger P3b amplitudes to nontarget stimuli (but not to hits), and larger frontal P3(1) amplitudes to infrequent than to frequent stimuli. It was hypothesized that in ADHD children in both the auditory and the visual task, there is a deficit in the activation of the P3b process. Incorrect triggering of the P3b process might be caused by disturbances in other aspects of the attention process, preceding the P3b.

Associations Between Event-Related Potentials and Measures of Attention and Inhibition in the Continuous Performance Task in Children With ADHD and Normal Controls

OBJECTIVES First, to differentiate between inattention and impulsivity based on type of errors made in the AX version of the Continuous Performance Task (CPT), and second, to investigate whether differences in performance between children with attention-deficit hyperactivity disorder (ADHD) and normal controls also occur in specific forms of brain activity, namely event-related potentials (ERPs), presumably related to inattention and impulsivity or inhibition. METHOD Sixteen ADHD and 16 normal control children performed the CPT-AX. ERPs were recorded at occipital (Oz), parietal (Pz), central (Cz), and frontal (Fz) leads. RESULTS The ADHD children had a higher CPT-Inattention score and showed smaller parietal positive waves at a latency of approximately 300 msec in reaction to target stimuli, target P3s, likewise indicating less attention. In contrast, they showed neither higher CPT-Impulsivity nor a smaller frontocentral negative wave at about 200 msec (N2); the N2 is generally seen as reflecting inhibition. A subgroup of children with ADHD and oppositional defiant disorder (n = 6) had smaller N2 waves than controls, however. CONCLUSIONS The ADHD group studied showed deficits in attention but not in impulsivity (or inhibition).

Perceptual and response interference in children with attention-deficit hyperactivity disorder, and the effects of methylphenidate

Fourteen children with attention-deficit hyperactivity disorder (ADHD) and 14 normal control children were compared with respect to stimulus- and response-related processes. Subjects with ADHD took part in two additional sessions under methylphenidate or placebo. In both experiments, performance and electrophysiological measures such as the P2, N2, and P3 components of event-related potential and electromyogram (EMG) activity were measured during an Eriksen flanker task. In both groups of children, reaction times (RTs) to arrow stimuli incongruent with the target were longer than those to neutral stimuli (response interference), which were again slower than RTs to target-alone stimuli (perceptual interference). Children with ADHD made more errors to incongruent stimuli and showed more response interference. For correct responses, no differences between the groups in response interference effects on reaction time, P2, N2, and P3 latency, or EMG onset were found. Methylphenidate had a general enhancing effect on accuracy but did not specifically reduce interference from the flanking stimuli. Methylphenidate had no effects on RT, N2 and P2 latency, P3 amplitude or latency, or EMG activity. The conclusion that methylphenidate did not influence response processes contrasts sharply with findings reported by authors using the Sternberg memory search task.

Looking at Images with Human Figures: Comparison Between Autistic and Normal Children

Based on clinical observations of abnormal gaze behavior of autistic children, it has been suggested that autistic children have a problem in processing social information. Several studies on eye movements have indeed found indications that children with autism show particularly abnormal gaze behavior in relation to social stimuli. However, the methodology used in such investigations did not allow for precise gaze analysis. In the present study, the looking behavior of autistic children toward cartoon-like scenes that included a human figure was measured quantitatively using an infrared eye-tracking device. Fixation behavior of autistic children was similar to that of their age- and IQ-matched normal peers. These results do not support the notion that autistic children have a specific problem in processing socially loaded visual stimuli. Also, there is no indication for an abnormality in gaze behavior in relation to neutral objects. It is suggested that the often-reported abnormal use of gaze in everyday life is not related to the nature of the visual stimuli but that other factors, like social interaction, may play a decisive role.

Eye movements, visual attention, and autism: a saccadic reaction time study using the gap and overlap paradigm

BACKGROUND On the basis of the literature on autism, it was hypothesized that children with autism have deficits in attentional (dis-)engagement mechanisms. METHODS A saccadic gap-overlap task was used to study visual engagement and disengagement in 16 high-functioning autistic children of about 10 years of age and 15 age- and IQ-matched normal control children. Subjects were asked to make saccadic eye movements from a fixation point to a suddenly appearing target as fast as possible. The saccadic reaction time was compared in two conditions: 1) the overlap condition, in which the fixation point was continuously visible, and 2) the gap condition, in which the fixation point was turned off 200 msec before the target appeared. RESULTS Although no differences between the groups in either condition was observed, the gap effect (i.e., the difference in saccadic reaction time between the overlap condition and the gap condition) was smaller in the autistic group than in the control group. CONCLUSIONS We concluded that autistic children show a lower level of attentional engagement.

Attentional capacity, a probe ERP study : differences between children with attention-deficit hyperactivity disorder and normal control children and effects of methylphenidate

In the present study it was investigated whether the smaller P3s in attention-deficit hyperactivity disorder (ADHD) children are caused by a shortage of capacity underlying P3 processes or whether they are due to a capacity allocation problem. Also, effects of methylphenidate on these processes were investigated. Performance and event-related potentials (ERPs) of 14 ADHD and 14 control children were measured using an irrelevant-probe technique. Three types of task irrelevant visual probes (standards, deviants, and novels) were presented against the background of two visual tasks that varied in task difficulty. The parietal P3 wave was measured in response to task stimuli and probes. ADHD subjects made significantly fewer correct detections than normal controls in both the easy and the hard tasks. Controls showed an enhanced P3 to task-relevant stimuli in the hard task, whereas ADHD children did not. Probe (novel) P3 amplitudes decreased from the easy to the hard task to the same extent in both groups. Methylphenidate enhanced the percentage of correct responses and task P3 amplitudes in both the easy and the hard task but probe P3 amplitudes were not influenced by methylphenidate. It was concluded that ADHD children do not suffer from a shortage in attentional capacity; rather, the evidence is in favor of a problem with capacity allocation. Furthermore, methylphenidate had enhancing effects on performance and ERPs, but did not improve the capacity-allocation deficit.

Effects of methylphenidate on event-related potentials and performance of attention-deficit hyperactivity disorder children in auditory and visual selective attention tasks

Attention-deficit hyperactivity disorder (ADHD) children participated in a double-blind placebo-controlled study in which the effects of a dosage of 15 mg methylphenidate (MPH) on auditory and visual selective attention tasks was determined by presenting frequent (90%) and infrequent (10%) stimuli in both relevant and irrelevant input channels. The subjects task was to respond to the infrequent tones in the relevant input channel. Processing activity (negativity and positivity) was assessed for both tasks. N1, P2, N2, and P3b peaks were scored in the auditory task and N1, P1, N2, P2, P3(1), and P3b peaks were scored in the visual task. Effects of MPH were more prevalent in the visual than in the auditory condition. In the visual condition MPH enhanced the percentage of hits, caused higher central, parietal, and occipital P3b amplitudes to attended stimuli (both standards and deviants), and also enhanced the frontal processing negativity (PN). In the auditory task MPH did not influence performance, but it enhanced the frontal PN as well as the parietal and occipital P3b amplitudes to all stimulus types. In ADHD children, MPH ameliorates some, but not all, deficits and also improves processing where no differences with normal children are present.

Visual and somatosensory event-related brain potentials in autistic children and three different control groups

Event-related potentials (ERPs) to visual and somatosensory stimuli, generated during an oddball task, were obtained in a group of autistic children and 3 control groups (normal, attention-deficit, and dyslectic children, respectively). The task included the presentation of standard, deviant, and novel stimuli and had a (between-group) passive vs. active (counting) condition. Research questions were whether (a) autistic children differ from other children with respect to the processing of visual and/or somatosensory stimuli, as measured in the amplitude of the N1, mismatch activity, and P3, (b) autistic children specifically have problems in the processing of distal (visual) stimuli, compared to the processing of proximal (somatosensory) stimuli, and (c) autistic children have an atypical lateralization pattern of ERP activity. Only in the autistic group a task effect on the visual P2N2 (mismatch activity) and larger P3s to novels than to deviants were found, in both the visual and the somatosensory modality. There also was a smaller occipital P3 to visual standard stimuli in the passive condition in the autistic group than in 2 control groups. We concluded that autistics (a) differ from several other groups of children with respect to the visual P2N2 and the visual and somatosensory P3, (b) show abnormalities in the processing of both proximal and distal stimuli, and (c) show no indication of abnormal lateralization of ERPs.

Split-Second Sequential Selective Activation in Human Secondary Visual Cortex

This work addressed early selection based on nonspatial visual features, using event-related potentials (ERPs) with high temporal resolution and dipole-source modeling. Subjects were presented rapid sequences of gratings varying in spatial frequency and orientation, and were instructed to attend to gratings with one spatial frequency and ignore those with another. Attention effects started at 120-msec latency as anterior positivity and proceeded as posterior negativity (200 msec) and anterior negativity (265 msec). Dipole-source modeling suggested that these effects reflect the sequential selective activation of, on average, posterior dorsalmedial, posterior ventrallateral, and anterior medial cortical areas. In contrast, stimulus-specific activity was observed well before 100-msec latency and characterized by dipoles with locations significantly posterior to those of the attention-modulated activity. These results indicate that even with highly discriminable spatial frequencies, selection is not as early as before the 100-msec latency, unlike what is often found for location selection. It is also separated in time and anatomically from the earliest stimulus-specific cortical activity. Reducing discriminability of the selection feature resulted in longer selection latencies, becoming manifest only at 175 msec as an apparent combination of posterior and anterior negativities, and in an elevated criterion for overt responding.