Visuospatial attentional shifts and choice responses of adults and ADHD and non-ADHD children

Distractibility and impulsivity neural states are distinct from selective attention and modulate the implementation of spatial attention

In the context of visual attention, it has been classically assumed that missing the response to a target or erroneously selecting a distractor occurs as a consequence of the (miss)allocation of attention in space. In the present paper, we challenge this view and provide evidence that, in addition to encoding spatial attention, prefrontal neurons also encode a distractibility-to-impulsivity state. Using supervised dimensionality reduction techniques in prefrontal neuronal recordings in monkeys, we identify two partially overlapping neuronal subpopulations associated either with the focus of attention or overt behaviour. The degree of overlap accounts for the behavioral gain associated with the good allocation of attention. We further describe the neural variability accounting for distractibility-to-impulsivity behaviour by a two dimensional state associated with optimality in task and responsiveness. Overall, we thus show that behavioral performance arises from the integration of task-specific neuronal processes and pre-existing neuronal states describing task-independent behavioral states.

Failing to detect relevant information has been assumed to be a consequence of misallocation of attention. Here, the authors present findings showing that optimal behavioral performance results from the absence of interference between internal neural states and attention control.

When attention is intact in adults with ADHD

Is covert visuospatial attention-selective processing of information in the absence of eye movements-preserved in adults with attention-deficit/hyperactivity disorder (ADHD)? Previous findings are inconclusive due to inconsistent terminology and suboptimal methodology. To settle this question, we used well-established spatial cueing protocols to investigate the perceptual effects of voluntary and involuntary attention on an orientation discrimination task for a group of adults with ADHD and their neurotypical age-matched and gender-matched controls. In both groups, voluntary attention significantly improved accuracy and decreased reaction times at the relevant location, but impaired accuracy and slowed reaction times at irrelevant locations, relative to a distributed attention condition. Likewise, involuntary attention improved accuracy and speeded responses. Critically, the magnitudes of all these orienting and reorienting attention effects were indistinguishable between groups. Thus, these counterintuitive findings indicate that spatial covert attention remains functionally intact in adults with ADHD.

Impaired reflexive orienting to social cues in attention deficit hyperactivity disorder

The present study investigated whether another person's social attention, specifically the direction of their eye gaze, and non-social directional cues triggered reflexive orienting in individuals with Attention Deficit Hyperactivity Disorder (ADHD) and age-matched controls. A choice reaction time and a detection tasks were used in which eye gaze, arrow and peripheral cues correctly (congruent) or incorrectly (incongruent) signalled target location. Independently of the type of the task, differences between groups were specific to the cue condition. Typically developing individuals shifted attention to the location cued by both social and non-social cues, whereas ADHD group showed evidence of reflexive orienting only to locations previously cued by non-social stimuli (arrow and peripheral cues) but failed to show such orienting effect in response to social eye gaze cues. The absence of reflexive orienting effect for eye gaze cues observed in the participants with ADHD may reflect an attentional impairment in responding to socially relevant information.

A novel visuospatial priming task for rats with relevance to Tourette syndrome and modulation of dopamine levels

Individuals with Tourette syndrome (TS) exhibit deficits in inhibitory information processing which may reflect impaired neural mechanisms underlying symptoms and which can be detected using a negative priming (NP) task. NP is the normal reduction of performance when identifying target stimuli that appear where non-target stimuli appeared previously. TS subjects exhibit diminished NP and their NP levels predict their response to behavioral therapy. Here we review relevant literature on this issue and also report a novel rat NP task. In the latter, rats respond to target stimuli (continuous light) while ignoring non-target stimuli (blinking light). Each trial was preceded by a prime in which target and non-target stimuli were briefly presented. Performance was challenged by shortening prime duration and by administering amphetamine. During the short prime challenge, rats exhibited lower accuracy in NP vs. baseline trials, indicative of inhibitory information processing. Modulation by amphetamine administration indicates that this drug had rate-dependent effects. Evidence is provided of individual differences in NP and response to the drug, with priming being reduced in high NP rats, while it was increased in low NP subjects. The rat NP task represents a novel and suitable tool for investigating the neural bases of inhibitory information processing and its dysfunction in TS.

Disengagement and inhibition of visual-spatial attention are differently impaired in children with rolandic epilepsy and Panayiotopoulos syndrome

We assessed voluntary orientation and reorientation of visuospatial attention in 313 healthy 6- to 22-year-old participants, 30 children suffering from benign epilepsy with centrotemporal spikes (BECTS) and 13 children with Panayiotopoulos syndrome (PS). The developmental section highlights the late development of reorienting skills. Only children with BECTS-R showed a strong tendency toward a rightward bias in attentional orientation. Additionally, a unilateral deficit of disengagement characterizes the patients with BECTS-R and comorbid ADHD. Right rolandic spikes seem to aggravate subclinical reorienting difficulties. Finally, children with PS failed to diffuse inhibition, except in the nearest area outside the attentional focus. This deficit could be attributed to the typical occipital-to-frontal spreading of the spikes in PS. By showing distinct attentional deficiencies according to the epileptic syndrome and the epileptic focus lateralization in BECTS, the results provide new evidence for alterations of attentional mechanisms by interictal epileptic activity, which probably contribute to learning difficulties.

Searching for the attention deficit in attention deficit hyperactivity disorder: the case of visuospatial orienting

We review all 14 extant studies of covert visuospatial attention in attention deficit hyperactivity disorder (ADHD) (total N=248). Metaanalysis showed that intriguing but isolated findings of alerting or posterior disengage deficits were too small to reliably detect with the sample sizes typically employed. Posterior move and engage operations and the vigilance sustained attention process were normal in ADHD. For exogenous cues, effect sizes for group differences were homogeneously small across all repeated-measures conditions, as were calculations of cost, benefit, and validity effects. For endogenous cues, effect sizes were heterogeneous; however, calculations of cost, benefit, and validity effects were small and homogenous. The most parsimonious conclusion may be that ADHD is not characterized by significant visual orienting dysfunction, but questions remain about the extent of anterior lateralized effects in the combined subtype and about attentional functioning in the inattentive subtype.

Evidence for a pure time perception deficit in children with ADHD

BACKGROUND

Deficits have been found previously in children with ADHD on tasks of time reproduction, time production and motor timing, implicating a deficit in temporal processing abilities, which has been interpreted as either secondary or primary to core executive dysfunctions. The aim of this study was to explore further the abilities of hyperactive children in skills of time estimation, using a range of time perception tasks in different temporal domains.

METHOD

Time estimation was tested in a verbal estimation task of 10 seconds. Time reproduction was also acquired for two time intervals of 5 and 12 seconds. A temporal discrimination task aimed to determine the idiosyncratic threshold of minimum time interval (in milliseconds) necessary to distinguish two intervals differing by approximately 300 milliseconds. Twenty-two children diagnosed with ADHD were compared to 22 healthy children, matched for age, handedness and working memory skills.

RESULTS

Children with ADHD were significantly impaired in their time discrimination threshold: on average, time intervals had to be 50 ms longer for the hyperactive children in order to be discriminated when compared with controls. Children with ADHD also responded earlier on a 12-second reproduction task, which however only approached significance after controlling for IQ and short-term memory. No group differences were found for the 5-second time reproduction or verbal time estimation tasks.

CONCLUSIONS

The findings suggest that children with ADHD perform poorly on time reproduction tasks which load heavily on impulsiveness and attentional processes and they also suggest that these children may have a perceptual deficit of time discrimination, which may only be detectable in brief durations which differ by several hundred milliseconds. A temporal perception deficit in the range of milliseconds in ADHD may impact upon other functions such as perceptual language skills and motor timing.

Is ADHD a disinhibitory disorder?

Attention deficit hyperactivity disorder (ADHD) is widely theorized to stem from dysfunctional inhibitory processes. However, the definition of inhibition is imprecisely distinguished across theories. To clarify the evidence for this conception, the author relies on a heuristic distinction between inhibition that is under executive control and inhibition that is under motivational control (anxiety or fear). It is argued that ADHD is unlikely to be due to a motivational inhibitory control deficit, although suggestions are made for additional studies that could overturn that conclusion. Evidence for a deficit in an executive motor inhibition process for the ADHD combined type is more compelling but is not equally strong for all forms of executive inhibitory control. Remaining issues include specificity to ADHD, whether inhibitory problems are primary or secondary in causing ADHD, role of comorbid anxiety and conduct disorder, and functional deficits in the inattentive ADHD subtype.

Material-specific and non-specific attention deficits in children and adolescents following temporal-lobe surgery

Attentional control in children and adolescents with unilateral temporal-lobe excisions was examined using two experimental tasks, a lexical-decision and a spatial-cue task, and a standardized vigilance task. Participants with left temporal excisions took longer than controls to reorient their attention after invalid cues compared to neutral cues in the lexical task and they made more errors on all three of the tasks. Participants with right temporal excisions differed from controls in the number of errors made on the spatial task. No differences were found between the lesion and control groups on reaction-time measures of the spatial task. The results suggest that a material-specific inhibition impairment, as well as a more general sustained attention deficit, may result after a left temporal excision in childhood or adolescence. These deficits are considered in the context of neuroanatomical models of attentional control.

Synchronization, anticipation, and consistency in motor timing of children with dimensionally defined attention deficit hyperactivity behaviour

We tested the hypothesis that children with hyperactive behaviour are impaired in the temporal organization of their motor output. The performance of 11 boys, scoring above a cut-off on standard scales of overactivity and inattention, was compared to that of controls in progressively more complex Motor-timing tasks. The tasks administered required self-paced and externally paced Sensorimotor Synchronization and Sensorimotor Anticipation. Deficits at a perceptual level were investigated with a Time-discrimination task. As hypothesized, we found that hyperactive children had no deficits in their perception of time but were impaired in timing their motor output. Hyperactive children were more inconsistent than controls in maintaining a freely chosen tapping rhythm, in synchronizing and in anticipating their motor response to external visual stimulation.

Effects of presentation rate of stimuli on response inhibition in ADHD children with and without tics

Presentation rate of stimuli is a crucial factor in Attention-deficit Hyperactivity Disorder (ADHD), that is, especially in ADHD children without tics ( n = 24), the ability to inhibit a response decreases in conditions with fast and slow presentation rates of stimuli.