The effect of reinforcement variables on inhibition in children with ADHD.

Behavioral inhibition, often cited as a central deficit in children with ADHD, has been shown to change in response to reinforcement. In this preliminary investigation, children with ADHD (n= 20) and matched controls (ages 7 to 12) completed a new version of the stop signal paradigm, the Fire Fighter Game, a measure of inhibition of a prepotent motor response, under three conditions: (1) no reinforcement; (2) immediate reinforcement; and (3) delayed reinforcement. In all conditions, the stop signal reaction time (SSRT) of children with ADHD was consistently longer than controls. Both groups improved significantly with reinforcement, and there was no strong evidence that immediate reinforcement was more effective than delayed reinforcement. However, it appeared that the reason for the changes in SSRT in response to reinforcement differed between the groups. Children in the control group responded faster on go trials, whereas children with ADHD improved their ability to inhibit responding with shorter stop delays. The relevance of these findings is discussed in terms of current theories of ADHD.     

Evidence for an Error Monitoring Deficit in Attention Deficit Hyperactivity Disorder

We studied error monitoring in ADHD and control children in a task requiring inhibition of a motor response. The extent of slowing following successful (stopped) and failed (nonstopped) inhibition was compared across groups. We also measured the time required to inhibit a response (stop signal reaction time, SSRT). Compared to controls, ADHD participants slowed less following nonstopped responses. Slowing did not vary with comorbid reading, oppositional, conduct or anxiety disorder, sex or ADHD subtype. Slowing after nonstopped responses was marginally, although significantly correlated with total ADHD symptoms and with age. ADHD participants had significantly longer SSRT than controls, but SSRT was not significantly correlated with slowing. The apparent deficit in error monitoring in ADHD and its independence from the inhibition deficit observed in ADHD has implications for executive control models of ADHD, performance problems associated with the disorder and for component theories of executive control.     

Reward improves cancellation and restraint inhibition across childhood and adolescence

Inhibitory control allows for the regulation of thought and action and interacts with motivational variables, such as reward, to modify behavior adaptively as environments change. The authors examined the effects of reward on two distinct forms of inhibitory control, cancellation and restraint. Typically developing children and adolescents completed 2 versions of the stop signal task (cancellation and restraint) under 3 reward conditions (neutral, low reward, and high reward), where rewards were earned for successful inhibitory control. Rewards improved both cancellation and restraint inhibition, with similar effects of reward on each form of inhibitory control. Rewards did not alter the speed of response execution in either task, suggesting that rewards specifically altered inhibition processes without influencing processes related to response execution. Adolescents were faster and less variable than children when executing and inhibiting their responses. There were similar developmental effects of reward on the speed of inhibitory control, but group differences were found in terms of accuracy of inhibition in the restraint task. These results clarify how reward modulates two different forms of regulatory behavior in children and adolescents.     

Hot and Cool Aspects of Cognitive Control in Children with ADHD: Decision-Making and Inhibition

This study investigated hot and cool aspects of cognitive control in children with Attention Deficit Hyperactivity Disorder (ADHD). The study aimed to: (1) replicate the postulated response inhibition deficit of children with ADHD; (2) explore whether children with ADHD choose disadvantageously in a decision-making task and to explore the mechanisms underlying the expected response pattern; and (3) study whether performance on a combination of hot and cool executive control measures has predictive value for an ADHD diagnosis. The sample consisted of 20 children with ADHD and 22 normal developing children (NC, 8 to 12 years) matched on age, FSIQ, and gender. Two paradigms have been applied: (1) the stop signal paradigm, and (2) the adapted children's version of the IOWA Gambling task. There were no group differences for both paradigms. Both groups chose in a reward-oriented manner and seemed to develop the ability to take future consequences into account in making decisions. Moreover, feedback resulted in direct behavioral changes. Children with ADHD did not have a specific response inhibition deficit or a decision-making deficit.     

The interplay of stop signal inhibition and inhibition of return

Inhibition of return (IOR) refers to slower responding to a stimulus that appears in the same rather than a different location as that of a preceding stimulus. The goal of the present study was to examine the relationship between IOR and stop signal inhibition. Participants were presented with two stimuli (S1 and S2) on each trial. On half of the trials (go trials), participants were required to make a speeded button-press response to report the location of S1; on the other half of trials (stop trials), they were required to cancel the response to S1, as indicated by the appearance of a stop signal at a variable delay (stop signal delay, SSD) after the appearance of S1. Success in cancelling an S1 response varied directly as a function of the SSD: The longer the delay, the more difficult it was for participants to cancel the prepared response. We examined the magnitude of IOR in the S2 reaction times as a function of whether participants made a correct go response to S1, made an erroneous non-cancelled response to S1, or successfully cancelled a response to S1. Our results indicated that the presentation of a stop signal increased the magnitude of IOR, even when the S1 response was not successfully cancelled. However, this was true only when the to-be-cancelled response involved the same effectors as the response used to reveal IOR. These results suggest that there may be a motor component to IOR that is sensitive to the same inhibitory processes that are used to cancel responses in a stop signal paradigm.     

Assessing inhibitory control: a revised approach to the stop signal task

The stop signal task (stop task) is designed to assess inhibitory control and is a frequently used research tool in clinical disorders such as ADHD and schizophrenia. Previous methods of setting stop signal delay and of assessing inhibitory control are problematic. The current study reports two modifications that improve the task as a measure of inhibitory control. The first modification was to set stop signal delays proportional to go mean reaction time (go MRT) to better account for inter-subject variability in go MRT. Twenty-eight normal children were tested, and all standard, stop task dependent measures were obtained when delays were set by this method. The second modification was to calculate a novel dependent measure called the area of inhibition (AOI) which provides a more complete measure of inhibitory control than the slope of the relative finishing time z-scores (ZRFT-slope). Implications for the assessment of inhibitory control in clinical populations are discussed.     

Novel Measures of Response Performance and Inhibition in Children with ADHD

Fifteen children with ADHD aged 8 to 12 years and age and gender matched controls performed two different stopping tasks to examine response performance and inhibition and their respective moment-to-moment variability. One task was the well-established stop-signal task, while the other was a novel tracking task where the children tracked a spaceship on the screen until an alarm indicated they should stop. Although performance was discrete in the stop signal task and continuous in the tracking task, in both tasks latencies to the stop signal were significantly slowed in children with ADHD. Go performance and variability did not significantly differ between ADHD and control children in either task. Importantly, stopping latency in the novel spaceship tracking task also was more variable in children with ADHD. As stopping variability cannot be measured using the standard stop signal task, the new task offers compelling support for the heretofore untested prediction that stopping is both slowed and more variable in children with ADHD. The results support a response inhibition impairment in ADHD, whilst limiting the extent of an intra-trial variability deficit.

Response inhibition in children with and without ADHD after traumatic brain injury

Children with attention‐deficit hyperactivity disorder (ADHD) and traumatic brain injury (TBI) show deficient response inhibition. ADHD itself is a common consequence of TBI, known as secondary ADHD (S‐ADHD). Similarity in inhibitory control in children with TBI, S‐ADHD, and ADHD would implicate impaired frontal‐striatal systems; however, it is first necessary to delineate similarities and differences in inhibitory control in these conditions. We compared performance of children with ADHD and those with TBI without pre‐injury ADHD on a stop signal, response inhibition task. Participants were 274 children aged 6–14 years. There were 92 children with ADHD, 103 children with TBI, and 79 typically developing children who served as controls. Among the TBI participants, injury severity ranged from mild to severe. Children with ADHD and TBI showed deficient inhibition. The deficit in children with ADHD was as great as or greater than that in children with TBI, regardless of degree of TBI severity or the presence of S‐ADHD. The finding indicates that TBI results in deficient inhibition regardless of the development of S‐ADHD.     

ADHD儿童的选择性抑制

采用较传统停止信号任务更为精确的选择性停止信号任务,探索ADHD的选择性抑制缺陷的机制。结果发现,ADHD儿童在选择性停止信号任务上,抑制失败的比率明显高于正常儿童,但是其执行加工速度和抑制加工速度与正常儿童没有差异,另外,ADHD儿童表现出了更大的反应变异性。研究认为,ADHD在选择性停止信号任务上的抑制缺陷并非由于抑制加工速度过慢所导致,而是由于其不能很好地维持最佳的激活状态所导致,状态调节理论更能反映ADHD的本质。     

To do or not to do? Prospective memory versus response inhibition in autism spectrum disorder and attention-deficit/hyperactivity disorder

In the present research, event-based prospective memory and response inhibition (RI) abilities were investigated in children with ASD (Study 1), with ADHD (Study 2), and their matched neurotypical controls. Children engaged in a categorisation (ongoing) task and, concurrently, in either an event-based prospective memory (PM) or a Go/No-Go secondary task. Results showed that, as compared to their matched controls, ASD children's performance was more impaired in the PM task than in the Go/No-Go task, while the performance pattern of ADHD children was reversed. In the ongoing task, ASD children were as accurate as, but significantly slower than, controls, independently of conditions. ADHD children did not differ from controls in the presence of a concurrent PM task, while they were less accurate than controls in the presence of the go/no-go task. Overall, the two patterns of findings suggest important differences in the way ASD and ADHD children remember and realise intentions requiring opposite behaviours (acting vs stopping).     

Exercise Improves Cognitive Control: Evidence from the Stop Signal Task

The aim of this study was to test the hypothesis that exercise improves executive control. We compared the performance of physically active and passive young participants in two versions of the stop signal task: a strategic (more executive) and a standard version. The results showed that active participants were more efficient than passive at inhibiting a response in the strategic version, suggesting that (1) physical exercise appears positively associated with improved cognitive control in healthy young participants, adding to evidence gathered in children, aging and clinical populations; and that (2) the strategic version of the stop signal task constitutes a more sensitive task than executive tasks previously used. Although the data point out a link between physical activity and executive control, they also have potential practical implications for health authorities and the general public by strengthening the view that exercise, beyond its physical health benefits, also has positive effects on cognitive functioning. Copyright © 2013 John Wiley & Sons, Ltd.     

Response Inhibition and ADHD Traits: Correlates and Heritability in a Community Sample

Endophenotypes or intermediate phenotypes are of great interest in neuropsychiatric genetics because of their potential for facilitating gene discovery. We evaluated response inhibition, latency and variability measures derived from the stop task as endophenotypes of ADHD by testing whether they were related to ADHD traits in the general population, heritable and shared genetic risk with ADHD traits. Participants were 16,099 children and adolescents, ages 6 to 18 years who visited a local science center. We measured ADHD traits using the Strengths and Weaknesses of ADHD-symptoms and Normal-Behavior (SWAN) rating scale and performance on the stop signal task (SST)—response inhibition (SSRT), response latency (GoRT), and response variability (GoRTSD). Regression analysis was used to assess the relationship of cognitive measures and ADHD traits while controlling for family, age, sex, ethnicity, socioeconomic status and treatment status. Heritability of ADHD and cognitive traits was estimated using SOLAR in 7,483 siblings from 3,507 families that included multiple siblings. Bivariate relationships between pairs of variables were examined. Individuals with greater ADHD trait scores had worse response inhibition, slower response latency, and greater variability. Younger participants and girls had inferior performance although the gender effects were minimal and evident in youngest participants. Inhibition, latency, variability, total ADHD traits, inattention and hyperactivity-impulsivity scores were significantly heritable. ADHD traits and inhibition, but not latency or variability were coheritable. In the largest study in the general population, we found support for the validity of response inhibition as an endophenotype of ADHD.     

Developmental trends in simple and selective inhibition of compatible and incompatible responses

This study examined age-related change in the ability to inhibit responses using two varieties of the stop signal paradigm. Three age groups (29 7-year-olds, 24 10-year-olds, and 28 young adults) performed first on a visual choice reaction task in which the spatial mapping between the go signal and response was varied between blocks. The choice task was then complicated by randomly inserting a visual stop signal on 30% of the trials. In the simple stop signal paradigm, the stop signal required the inhibition of the planned response. In the selective stop signal paradigm, the stop signal required response inhibition only when the stop signal was presented at the same side as the instructed response to the go signal. The results showed that simple stopping was faster than selective stopping and that selective, but not simple, stopping of incompatible responses was slower than stopping of compatible responses. Brinley plot analysis yielded linear functions relating children's latencies to adults' latencies. Analysis of shared variance indicated that developmental change in the speed of selective stopping continued to be significant even when the effect associated with simple stopping was removed. This pattern of findings is discussed vis-à-vis notions of global versus specific developmental trends in the speed of information processing.     

Does response variability predict distractibility among adults with attention-deficit/hyperactivity disorder?

Increased intraindividual variability in response time (RTSD) has been observed reliably in attention-deficit/hyperactivity disorder (ADHD) and has often been used as a measure of inattention. RTSD is assumed to reflect attentional lapses and distractibility, though evidence for the validity of this connection is lacking. We assessed whether RTSD is an indicator of inattention by comparing RTSD on the stop-signal task (SST) with performance on the delayed oculomotor response (DOR) task, a measure of distractibility. Participants included 30 adults with ADHD and 28 controls. Participants completed the SST and the DOR task, which measured subjects' ability to maintain attention and avoid distraction by inhibiting reflexive saccades toward distractors. On the SST, the ADHD group was slower to inhibit than were controls, indicating poorer inhibitory control in ADHD. The ADHD group also displayed slower reaction times (RTs), greater RTSD, and more omission errors. On the DOR task, the ADHD group displayed more premature saccades (i.e., greater distractibility) than did controls. Greater variability in RT was associated with increased distraction on the DOR task, but only in ADHD participants. Results suggest that RTSD is linked to distractibility among adults with ADHD and support the use of RTSD as a valid measure of inattention in ADHD.     

IMPULSIVITY AND INHIBITORY CONTROL

Abstract— We report an experiment testing the hypothesis that impulsive behavior reflects a deficit in the ability to inhibit prepotent responses Specifically, we examined whether impulsive people respond more slowly to signals to inhibit (stop signals) than non-impulsive people In this experiment, 136 undergraduate students completed an impulsivity questionnaire and then participated in a stop-signal experiment, in which they performed a choice reaction time (go) task and were asked to inhibit their responses to the go task when they heard a stop signal The delay between the go signal and the stop signal was determined by a tracking procedure designed to allow subjects to inhibit on 50% of the stop-signal trials. Reaction time to the go signal did not vary with impulsivity, but estimated stop-signal reaction time was longer in more impulsive subjects, consistent with the hypothesis and consistent with results from populations with pathological problems with impulse control.     

The development of selective inhibitory control: The influence of verbal labeling

The role of language in the development of selective inhibitory control was examined in four groups: Children aged 7-9 years, children aged 11-13 years, adults aged 20-27 years, and adults aged 62-76 years. We used a modified stop-signal task in which participants inhibited or executed responses based on a visual signal. Response execution and inhibition were assessed by measurement of reaction times (RTs) and error rates to a go signal and RTs to a stop signal. Four task variations were compared in which subjects named (1) the stimulus, (2) the intended action (go/stop), (3) something irrelevant, or (4) nothing. Results showed different developmental trends for response execution and inhibition across the lifespan. Moreover, response execution was faster and more accurate when subjects named the stimulus instead of the intended action. The increase in response accuracy when naming the stimulus was greatest for children. In contrast to expectations, naming the intended action did not influence response inhibition. Overall, these findings suggest that verbal labeling supports the initiation but not the inhibition of actions.     

Priming Sentence Production in Adolescents and Adults with Attention-Deficit/Hyper-Activity Disorder

Theoretical accounts of attention-deficit/hyperactivity disorder (ADHD) posit a prominent role for problems in response inhibition (Nigg 2006). A key avenue for impulsivity in children with ADHD is inappropriate language expression. In this study, we sought to determine whether poor inhibitory control affects language production in adolescents and adults with ADHD. One hundred and ninety-five participants (13–35 years old; 65% male) were presented with two pictures and a verb, and their task was to form a sentence. If deficits in response inhibition affect language production, then participants with ADHD should be more likely than non-ADHD controls to begin speaking before having formulated a plan that will allow a grammatical continuation. The results showed that the ADHD-combined subtype, in particular, was more likely to produce an ungrammatical sequence. Effects were not moderated by age or gender. These data suggest that response suppression deficits in ADHD adversely affect the basic processes of sentence formation.     

奖赏通过增强信号监测提升认知控制

认知控制是动态的、过程性的认知调控, 涉及监测和控制两个过程。先前研究表明奖赏可以提升认知控制, 但是奖赏是通过增强信号监测来提升认知控制的, 还是作用于控制过程来提升认知控制的, 是一个有待研究的重要问题。在本研究中, 我们设计了三个实验来调查这一问题。实验1采用Stop-Signal任务验证奖赏是否能提升认知控制; 实验2通过改变反应规则将Stop-Signal任务信号监测加工分离出来, 探讨实验1中奖赏的提升作用是否来源于奖赏对信号监测的增强; 实验3通过操纵注意资源损耗分析, 考察注意资源分配对信号监测的促进作用。实验1结果显示, 个体能更快地根据奖赏信息做出抑制反应。实验2结果表明, 在信号监测任务中, 个体能更加快速地监测到与当前抑制状态相冲突且和奖赏相关的反应信号, 据此可认为奖赏通过增强对相关信号的监测, 有助于个体更早地启动奖赏刺激信号所对应的反应, 更高效地控制冲突。实验3结果说明, 当任务难度增大, 注意资源损耗, 奖赏相关信号的反应时和正确率仍优于无奖赏信号, 说明注意资源的分配可以调节相关信号的监测速度。总体来看, 本研究通过一系列实验表明, 以目标为导向的行为发生过程中, 奖赏能有效提升认知控制效率, 其关键机制在于通过注意资源分配增强相关信号的监测。     

激活水平对两亚型ADHD儿童反应执行与抑制能力的影响

研究选取了混合型ADHD儿童14名,注意缺陷型ADHD儿童16名以及正常儿童18名,考察了在不同激活水平下,两亚型ADHD儿童之间,及其与正常儿童之间的反应执行能力与抑制能力的异同。采用传统的go/no-go任务,并将刺激间的时间间隔设置为1秒、4秒、8秒三种条件,分别对应高、中、低三种激活水平。结果发现,(1)与正常儿童相比,ADHD儿童的反应执行能力更容易受到激活水平的影响,且两亚型ADHD儿童受到的影响模式基本一致。具体而言:在高激活水平下,ADHD儿童与正常儿童差异最小;在中、低激活水平下,ADHD儿童与正常儿童差异增大,表明ADHD儿童状态调节能力落后。(2)两亚型ADHD儿童的功能缺损模式不同,混合型儿童在状态调节和反应抑制两方面都存在缺损,且其反应抑制缺陷不受激活水平影响;注意缺陷型儿童仅在状态调节方面受损。     

The interaction between stop signal inhibition and distractor interference in the flanker and Stroop task

In the present study, two experiments were conducted to investigate the interaction between the behavioral inhibition, measured by the stop signal task, and distractor interference, measured by the flanker task and the Stroop task. In the first experiment, the stop signal task was combined with a flanker task. Analysis revealed that participants responded faster when the distractors were congruent to the target. Also, the data suggest that it is more difficult to suppress a reaction when the distractors were incongruent. Whether the incongruent distractor was part of the response set (i.e. the distractor could also be a target) or not, had no influence on stopping reactions. In the second experiment, the stop signal task was combined with a manual version of the Stroop task and the degree of compatibility was varied. Even though in the second experiment of the present study interference control is differently operationalized, similar results as in the first experiment were found, indicating that inhibition of motor responses is influenced by the presentation of distracting information that is not part of the response set.