When perceptual or motor sets are changed: Effects of updating demands on structure and energy of P300

It was attempted to disentangle the effect of two updating processes on P300. Three conditions were created by a priming paradigm: (1) No updating, (2) updating perceptual but no motor information, and (3) updating both perceptual and motor information. As expected, both updating conditions led to a P300-complex with more energy, but the additional demand of motor updating did not affect P300. Effects were similar for both delayed (experiment 1) and immediate responding (experiment 2).

Both experiments confirmed earlier observations that P300 consists of at least three subcomponents, namely P3a, P3b, and a positive Slow Wave (pSW). Perceptual updating affected in particular the energy of P3b and pSW. Further, pSW was related to the complexity of the updating operations. When stimuli consisted of abstract symbols there was more energy in pSW than when stimuli were concrete symbols with direct spatial relations to the response.

The structure and energy changes of P300 suggest that P3b and pSW do not provide an unambiguous picture of the underlying source structure. In some conditions only one peak (P3b) was observed in the surface structure; this still seemed to be the result of two underlying waves. In other conditions these waves were separated in time showing a clear double peak in the surface structure.     

Methylphenidate reduces abnormalities of stimulus classification in adolescents with attention deficit disorder.

Forty-eight adolescents with attention deficit disorder (ADD) received placebo and methylphenidate (M = 35.21 mg/day) for 3 consecutive weeks each. ADD patients who received placebo in the first phase of treatment were compared with unmedicated normal adolescents. ADD and normal adolescents did not differ in slope of reaction time as a function of memory load in a Sternberg (1969) memory task. These results may be interpreted as reflecting normal rates of memory search in ADD. However, in comparison with normal subjects, ADD subjects made disproportionately more errors to targets and lacked faster latencies of the P3b component of event-related potentials for targets than nontargets. These findings suggest abnormalities in stimulus classification. Methylphenidate did not affect ADD patients' rates of memory search, but it did reduce misclassifications of targets at high memory loads. The drug also evoked the normal pattern of slower P3b latencies for nontargets by shortening latencies for targets. Thus the stimulant reduced ADD adolescents' abnormalities in stimulus classification.     

Flanker effects with faces may depend on perceptual as well as emotional differences

Do threatening or negative faces capture attention? The authors argue that evidence from visual search, spatial cuing, and flanker tasks is equivocal and that perceptual differences may account for effects attributed to emotional categories. Empirically, the authors examine the flanker task. Although they replicate previous results in which a positive face flanked by negative faces suffers more interference than a negative face flanked by positive faces, further results indicate that face perception is not necessary for the flanker-effect asymmetry and that the asymmetry also occurs with nonemotional stimuli. The authors conclude that the flanker-effect asymmetry with affective faces cannot be unambiguously attributed to emotional differences and may well be due to purely perceptual differences between the stimuli.     

Methylphenidate Does Not Modify the Impact of Response Frequency or Stimulus Sequence on Performance and Event-Related Potentials of Children with Attention Deficit Hyperactivity Disorder

Twenty-six children with attention deficit/hyperactivity disorder (ADHD) participated in a double-blind trial consisting of 2 consecutive weeks each of placebo and methylphenidate (M = 26.92 mg/day = 0.78 mg/kg/day). As expected, stimulant therapy resulted in moderate weight loss, increased somatic complaints, and teacher and parent reports of reduced inattentiveness, aggression, and oppositionality. In both phases of the trial, patients were tested in a choice reaction time task assessing two aspects of the task that presumably affect response selection: response frequency (ratio of targets/nontargets = 25/75 vs. 50/50) and stimulus sequence (alternations vs. repetitions). Both manipulations yielded expected results on performance and event-related potentials (ERPs). Stimulant treatment increased accuracy and speed among younger children and curtailed variability of reaction time for the sample as a whole. However, methylphenidate did not affect ERPs. In combination, the results imply that the enhancement of performance by methylphenidate does not involve the demands of response selection examined in this study.     

Methylphenidate slows reactions of children with attention deficit disorder during and after an error

A Sternberg memory search task was administered under placebo and methylphenidate to 42 children with cross-situational attention deficit disorder (ADD), 31 children with cross-situational ADD plus oppositional features, and 25 patients with marginal ADD. Overall, stimulant medication enhanced accuracy and speed. In addition, patients reacted faster on correct responses not preceded by an error than on errors (especially false alarms) or on correct responses following an error. The slowness during error reactions may reflect decreased confidence or confusion during stimulus classification. This uncertainty may also lead subjects to respond with greater caution, hence more slowly, on correct responses following errors. Notably, methylphenidate increased the slowing of reactions on error trials as well as on correct reactions following an error. Stimulant medication may augment subjects' persistence when they are uncertain or confused, thereby heightening caution and promoting accuracy on succeeding trials. Consistent with previous reports of the generality of enhancement of performance by stimulant medication, the impact of methylphenidate was comparable for the three subtypes of ADD studied.Jaine Strauss is at Macalester College.This research was supported by National Institute of Mental Health Grants MH32103 and MH38118. We thank Rachel Avery, Christine Carriuolo, Lawrence Ota, the late Helen Pollock, and the University of Rochester's Strong Memorial Hospital Pharmacy for their assistance.     

Methylphenidate speeds evaluation processes of Attention Deficit Disorder adolescents during a continuous performance test

Fortysix Attention Deficit Disorder (ADD) adolescents took a Continuous Performance Test (CPT) under placebo and methylphenidate (35.33 mg/day). The task required pressing one button for targets (p=133),and another button for nontargets. Subjects displayed a strong bias to make the more frequent negative response before completely evaluating stimuli. Consistent with this assumption, subjects responded faster (by an average of 87 ms) to nontargets than to targets. Methylphenidate increased accuracy and speeded reaction times (RTs) to targets. The drug also increased the amplitude of the P3b component of the eventrelated potential for nontargets and shortened the latency of P3b for both targets and nontargets. These results suggest increased capacity allocation to and faster evaluation of task stimuli. Finally, the stimulant lengthened relative motor processing time (RT-P3b latency) for nontargets, a finding implying that response processing was accomplished with the benefit of earlier completion of evaluation processes for these stimuli.Portions of these findings were reported at the meeting of the Society for Research in Child and Adolescent Psychopathology, Costa Mesa, California, January 24–26, 1990. This research was supported by NIMH grant MH38118 to the first author. We thank the late Helen Pollock and the University of Rochester's Strong Memorial Hospital Pharmacy Manufacturing Department for their help.     

Performance and Private Speech of Children with Attention-Deficit/Hyperactivity Disorder While Taking the Tower of Hanoi Test: Effects of Depth of Search,Diagnostic Subtype,and Methylphenidate

We administered the Tower of Hanoi to demographically comparable samples of control participants (n = 34) and children with the Combined (n = 22) and Inattentive subtypes (n = 19) of Attention-Deficit/Hyperactivity Disorder (ADHD). Controls excelled over children with the Inattentive subtype, who outperformed patients with the Combined subtype. These results replicated findings of greater executive deficits in the Combined than in the Inattentive type of ADHD. Double-blind administration of methylphenidate improved task performance only for patients with the Inattentive subtype. In a drug-free Baseline session, children with both subtypes of ADHD made more private verbalizations than controls, particularly when failing puzzles. In later sessions, regardless of drug condition, the inattentive sample exhibited a smaller increase in self-regulatory utterances under failure. In contrast, the combined sample decreased self-regulatory verbalizations under failure only under methylphenidate. The results support some differences between the two subtypes of ADHD in executive functioning and in their response to stimulant therapy. Portions of these results were submitted as part of H. Theresa Chang's PhD dissertation (Chang, 2000) and Helena Kopecky's unpublished master's research, both conducted at the University of Rochester and supervised by Rafael Klorman.