Distractor Stimuli Research Articles

Testing Computational Models of Dopamine and Noradrenaline Dysfunction in Attention Deficit/Hyperactivity Disorder

We test our neurocomputational model of fronto-striatal dopamine (DA) and noradrenaline (NA) function for understanding cognitive and motivational deficits in attention deficit/hyperactivity disorder (ADHD). Our model predicts that low striatal DA levels in ADHD should lead to deficits in 'Go' learning from positive reinforcement, which should be alleviated by stimulant medications, as observed with DA manipulations in other populations. Indeed, while nonmedicated adult ADHD participants were impaired at both positive (Go) and negative (NoGo) reinforcement learning, only the former deficits were ameliorated by medication. We also found evidence for our model's extension of the same striatal DA mechanisms to working memory, via interactions with prefrontal cortex. In a modified AX-continuous performance task, ADHD participants showed reduced sensitivity to working memory contextual information, despite no global performance deficits, and were more susceptible to the influence of distractor stimuli presented during the delay. These effects were reversed with stimulant medications. Moreover, the tendency for medications to improve Go relative to NoGo reinforcement learning was predictive of their improvement in working memory in distracting conditions, suggestive of common DA mechanisms and supporting a unified account of DA function in ADHD. However, other ADHD effects such as erratic trial-to-trial switching and reaction time variability are not accounted for by model DA mechanisms, and are instead consistent with cortical noradrenergic dysfunction and associated computational models. Accordingly, putative NA deficits were correlated with each other and independent of putative DA-related deficits. Taken together, our results demonstrate the usefulness of computational approaches for understanding cognitive deficits in ADHD.

Category-level contributions to the alphanumeric category effect in visual search

Do letter and digit recognition depend on the same or different cognitive mechanisms? Letters are detected more quickly among digits than among letters; likewise, digit search is facilitated when distractors are letters, as opposed to digits. This effect suggests that different mechanisms underlie recognition of these two categories. There are, however, systematic physical differences between letters and digits that might account for the effect. We used target and distractor stimuli that facilitated within-category search when inverted, and category identity was, thereby, attenuated. However, in conditions of upright search, in which category identity was more salient, between-category search was more efficient for the same stimuli. These findings suggest that letter and digit recognition are, at least to a degree, functionally independent.

Letter identification processes in reading: Distractor interference reveals an automatically engaged, domain-specific mechanism

Recent neuroimaging studies have revealed that letters activate both the left and the right fusiform areas, but that only the left fusiform responds to letters more than to control stimuli (Cohen et al., 2003). Though these findings suggest that the left fusiform is specialized in its function of identifying letters, it does not rule out the possibility that the right fusiform contributes critically to letter identification processes. We used a behavioural word identification task in which we compared bilateral and unilateral displays to determine the cost of engaging the right hemisphere with a distractor stimulus. We found that while engaging the left hemisphere led to a robust interference effect, engaging the right hemisphere had no effect at all. We were able to rule out an attentional bias to the right visual field as a possible explanation of the asymmetrical interference effect. We conclude that while the right hemisphere may be able to assume letter identification processing responsibilities in some patients with brain damage, the right hemisphere does not contribute critically to abstract letter identification processes in healthy right-handed individuals.

Relative ability of young and mature muscles to respond to limb lengthening

The response of the muscle is critical in determining the functional outcome of limb lengthening. We hypothesised that muscle response would vary with age and therefore studied the response of the muscles during tibial lengthening in ten young and ten mature rabbits. A bromodeoxyuridine technique was used to identify the dividing cells. The young rabbits demonstrated a significantly greater proliferative response to the distraction stimulus than the mature ones. This was particularly pronounced at the myotendinous junction, but was also evident within the muscle belly. Younger muscle adapted better to lengthening, suggesting that in patients in whom a large degree of muscle lengthening is required it may be beneficial to carry out this procedure when they are young, in order to achieve the optimal functional result.

Response inhibition in motor and oculomotor conflict tasks: Different mechanisms, different dynamics?

Previous research has shown that the appearance of task-irrelevant abrupt onsets influences saccadic eye movements during visual search and may slow down manual reactions to target stimuli. Analysis of reaction time distributions in the present study offers evidence suggesting that top-down inhibition processes actively suppress oculomotor or motor responses elicited by a salient distractor, in order to resolve the conflict that arises when reflex-like and deliberate responses are in opposition. Twenty-six participants carried out a variation of the oculomotor capture task. They were instructed to respond with either a saccade toward or with a button press at the side of the hemifield in which a target color singleton appeared. A distractor stimulus could appear either in the same or in the opposite hemifield. Delta plots revealed competition between reflex-like and deliberate response activation, and highlighted selective inhibition of automatic responses: While participants generally responded more slowly in incongruent compared to congruent situations, this effect diminished and even reversed in the slowest speed quantiles. These effects were present in both the oculomotor and motor response-mode conditions.

Motion by Nearby Players Biases Perception but Not Action in Judgments of Baseball Destination

In this research, the influence of irrelevant reference frames on estimates of ball destination was examined. In 3 experiments, confederate base runners and fielders served as distractor stimuli while balls were rolled from home plate to random locations along a barrier hidden under an elevated tarp between first and second base. Stationary participants estimated the position that the ball would exit from under the tarp if there were no barrier, whereas running participants ran along the back edge of the barrier and touched the top of the tarp above where they believed the ball would exit. Estimates of ball destination were significantly biased in the direction opposite to the confederates' motion for stationary participants, but were accurate for running participants. These findings are consistent with other perception-action dissociations, and show that relative motion effects can occur in a naturalistic setting.

Semantic priming effects from single words in a lexical decision task

The present research examines the semantic priming effects of a centrally presented single prime word to which participants were instructed to either “attend and remember” or “ignore”. The prime word was followed by a central probe target on which the participants made a lexical decision task. The main variables manipulated across experiments were prime duration (50 or 100 ms), the presence or absence of a mask following the prime, and the presence (or absence) and type of distractor stimulus (random set of consonants or pseudowords) on the probe display. There was a consistent interaction between the instructions and the semantic priming effects. Relative to the “attend and remember” instruction, an “ignore” instruction produced reduced positive priming from single primes presented for 100 ms, irrespective of the presence or absence of a prime mask, and regardless of whether the probe target was presented with or without distractors. Additionally, reliable negative priming was found from ignored primes presented for briefer durations (50 ms) and immediately followed by a mask. Methodological and theoretical implications of the present findings for the extant negative priming literature are discussed.

Effects of Task Difficulty and Target Likelihood in Area V4 of Macaque Monkeys

Spatial attention improves performance at attended locations and correspondingly modulates firing rates of cortical neurons. The size of these behavioral and neuronal effects depends on the difficulty of the task performed at the attended location. Psychological theorists have attributed this to a tighter focus of a fixed amount of processing resource at the attended location, but the effects of task difficulty on the distribution of neuronal effects of attention across the visual field have not been fully explored. We trained rhesus monkeys to do a detection task in which difficulty and spatial attention were manipulated independently. Probe stimuli were used to measure behavioral performance in different conditions of attention and difficulty. Animals performed better at attended locations and this advantage increased with difficulty, consistent with data from human psychophysics. Neuronal modulation by spatial attention was larger with greater difficulty. In two animals, increasing difficulty caused a modest increase in neuronal responses to visual stimuli regardless of the locus of spatial attention. In a third animal, which was previously trained to ignore multiple distracting stimuli, increasing task difficulty increased responses at the focus of attention and suppressed responses away from the focus of attention. The results show that difficulty can modulate effects of spatial attention in V4; it can alter the distribution of sensory responses across the visual scene in ways that may depend on the subject's behavioral strategy.

Saccadic trajectory in Huntington's disease

Trajectories of saccadic eye movements can be modulated by the presence of a competing visual distractor. It is proposed that the superior colliculus (SC) controls the initial deviation through competitive lateral interactions. Given the ramifications of connections between basal ganglia (BG) thalamo-cortical circuitry and the SC, it was anticipated that this modulation would be differentially effected in those with Huntington's disease, which in its early stages is primarily a disorder of the BG. Horizontal deviation was determined for exogenously driven and endogenously driven vertical saccades in the presence of peripheral distractors. For neurologically healthy participants, the initial trajectories of both saccade types curved away from distractor locations, as predicted. However, for HD participants exogenous saccades consistently deviated leftwards, irrespective of distractor location. Endogenous saccades also revealed anomalous horizontal deviation, with significant leftward deviation evident for saccades directed upward and significant rightward deviation for saccades directed downward. Further, both groups generated a comparable proportion of erroneous responses to distractor stimuli, but only neurologically healthy participants demonstrated a response time advantage for compatible target/distractor presentation. These results suggest anomalous regulation of distractor-related activity in HD.

Event-related brain potential correlates of emotional face processing

Results from recent event-related brain potential (ERP) studies investigating brain processes involved in the detection and analysis of emotional facial expression are reviewed. In all experiments, emotional faces were found to trigger an increased ERP positivity relative to neutral faces. The onset of this emotional expression effect was remarkably early, ranging from 120 to 180ms post-stimulus in different experiments where faces were either presented at fixation or laterally, and with or without non-face distractor stimuli. While broadly distributed positive deflections beyond 250ms post-stimulus have been found in previous studies for non-face stimuli, the early frontocentrally distributed phase of this emotional positivity is most likely face-specific. Similar emotional expression effects were found for six basic emotions, suggesting that these effects are not primarily generated within neural structures specialised for the automatic detection of specific emotions. Expression effects were eliminated when attention was directed away from the location of peripherally presented emotional faces, indicating that they are not linked to pre-attentive emotional processing. When foveal faces were unattended, expression effects were attenuated, but not completely eliminated. It is suggested that these ERP correlates of emotional face processing reflect activity within a neocortical system where representations of emotional content are generated in a task-dependent fashion for the adaptive intentional control of behaviour. Given the early onset of the emotion-specific effects reviewed here, it is likely that this system is activated in parallel with the ongoing evaluation of emotional content in the amygdala and related subcortical brain circuits.

The Influence of Various Distraction Stimuli on Affective Responses to Cycle Ergometry

Acute bouts of exercise have been associated with significant affective changes. Exercise supplemented with distraction stimuli may divert attention from feelings of fatigue and discomfort that are common during bouts of exercise to more pleasant feelings. However, many studies focus on auditory stimuli rather than visual stimuli. PURPOSE: The purpose of this study was to compare individuals' affective responses to exercise with visual, auditory and no distraction. METHODS: 29 individuals (20.5±1 .4 years) volunteered for this investigation. This study included three 30 min cycle ergometry exercise conditions, a control condition with no stimuli (NS) and 2 test conditions; one supplemented with a video (VS) and a second involving music (MS). Both stimuli were self-selected and administered in a random order. The Activation Deactivation Adjective Check List (ADACL), the Feeling Scale (FS), and the Felt-Arousal Scale (FAS) were given to the participants prior to, immediately following, 10 min post and 60 min post an acute bout of cycle ergometry. The ADACL assesses affect in the following dimensions: energetic arousal (EA; energy to tiredness) and tense arousal (TA; calm to tension). The FS assesses affective valences ranging from “very good” to “very bad”. The FAS assesses activation ranging from “low arousal” to “high arousal”. It was hypothesized that immediately after the acute bouts of exercise; positive affective responses will be highest after the video condition, followed by the music condition and lastly, the control condition. RESULTS: The data revealed a significant time effect for the FS, FAS, TA and EA. FS was significantly higher for the music and video groups compared to the no stim group (VS: 2.5±0.3;MS: 2.5±0.3;NS: 1.9±0.3; p<.01) and TA was significantly lower for the video group in comparison to the other 2 conditions (VS: 20.4±0.7; MS: 21.9±0.7; NS: 21.4±0.7; p<.03). There were no time by condition interactions for any of the data. CONCLUSION: These data seem to indicate that when given a distraction, an exerciser may experience greater feelings of pleasure when exercising with some type of distraction. This effect may be accentuated when considering feelings of tension in particular when video distraction is applied. The video distraction condition appears to be superior to the music condition due to its effect on both pleasurable feelings and tension during exercise. Application of these findings may have a positive influence on both adherence and compliance.

Time Course of Oculomotor Inhibition Revealed by Saccade Trajectory Modulation

Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Both target and distractor stimuli activate populations of neurons in topographic oculomotor maps such as the superior colliculus. Local inhibitory interconnections between these populations ensure only one saccade target is selected. Suppressing saccades to distractors may additionally involve inhibiting corresponding map regions to bias the local competition. Behavioral evidence of these inhibitory processes comes from the effects of distractors on oculomotor and manual trajectories. Individual saccades may initially deviate either toward or away from a distractor, but the source of this variability has not been investigated. Here we investigate the relation between distractor-related deviation of trajectory and saccade latency. Targets were presented with, or without, distractors, and the deviation of saccade trajectories arising from the presence of distractors was measured. A fixation gap paradigm was used to manipulate latency independently of the influence of competing distractors. Shorter-latency saccades deviated toward distractors and longer-latency saccades deviated away from distractors. The transition between deviation toward or away from distractors occurred at a saccade latency of around 200 ms. This shows that the time course of the inhibitory process involved in distractor related suppression is relatively slow.

P3a from auditory white noise stimuli

Objective P3a and P3b event-related brain potentials (ERPs) were elicited with an auditory 3-stimulus (target, distracter, standard) paradigm in which subjects responded only to the target. Methods Distracter stimuli consisted of white noise, novel sounds, or a high frequency tone, with stimulus characteristics perceptually controlled. Task difficulty was varied as easy and hard by changing the pitch difference between the target and standard stimuli. Results Error rate was greater and response time longer for the hard task. P3a distracter amplitude was largest for the white noise and novel stimuli, with maximum amplitude over the central recording sites, and larger for the hard discrimination task. P3b target amplitude was unaffected by distracter type, maximum over the parietal recording sites, and smaller and later for the hard task. Conclusions The findings indicate that white noise stimuli can produce reliable P3a components. Significance White noise can be useful for clinical P3a applications, as it removes the variability of stimulus novelty.

Auditory dominance in the error correction process: A synchronized tapping study

The goal of this study was to reveal auditory dominance in the error correction process that operates in the synchronized tapping paradigm. We presented six female subjects with a sound and a flash, alternately and successively. The subjects' task was to tap in synchrony with the sequence of the attended to modality (the target sequence). The inter-onset interval of the target sequence was 996 ms but varied irregularly between 996 − α ms and 996 + α ms for the distractor sequence. We found that tapping accuracy was influenced by the irregularity of the distractor sequence. As distractor stimuli were temporally separated from target stimuli, auditory–visual integration in timing did not occur in our experiment. Therefore, the irregularity of the distractor sequence must have directly influenced the error correction process in timing and not indirectly by affecting the target sequence to subsequently influence the error correction process. We also found that tapping accuracy was influenced by the irregularity of the auditory distractor, even when the irregularity was unnoticeable, but it was not affected by the irregularity of the visual distractor when the irregularity was unnoticeable, which suggests that the error correction process is located before, or is independent of, the perception of irregularity in timing. We conclude that the error correction process depends more on temporal information from the auditory system than on information from the visual system.

Neural correlates of performance trade-offs and dual-task interference in bimanual coordination: An ERP investigation

Previous behavioural studies have provided a framework for understanding coordination dynamics using traditional dual-task methodology. The central cost associated with stabilising bimanual coordination patterns has been inferred from performance trade-offs during the concurrent performance of a probe reaction time (RT) task. The present study aimed to provide a direct measure of central cost by assessing electrophysiological correlates of performance trade-offs under dual-task conditions. Event-related potentials (ERPs) were recorded from 16 participants while an anti-phase bimanual coordination task and a visual three-stimulus task were performed under single task conditions and under dual-task conditions in which either task was prioritised. The visual task required a foot response to low probability target stimuli, while low probability distracter and high probability standard stimuli were ignored. Consistent with previous research, there was a performance trade-off between pattern stability and RT to visual targets when the coordination task was prioritised relative to when the visual task was prioritised. This was accompanied by a significant reduction in central P3a amplitude elicited by distracter stimuli and parietal P3b amplitude elicited by target stimuli. These findings indicate that prioritisation and thus stabilisation of the motor task reduced the amount of central/perceptual and automatic attentional resources available to perform the visual task providing insight into CNS mechanisms that constrain the coordination of movement through the allocation of attentional resources.

Visual Clutter Causes High-Magnitude Errors

Perceptual decisions are often made in cluttered environments, where a target may be confounded with competing “distractor” stimuli. Although many studies and theoretical treatments have highlighted the effect of distractors on performance, it remains unclear how they affect thequality of perceptual decisions. Here we show that perceptual clutter leads not only to an increase in judgment errors, but also to an increase in perceived signal strength and decision confidence on erroneous trials. Observers reported simultaneously the direction and magnitude of the tilt of a target grating presented either alone, or together with vertical distractor stimuli. When presented in isolation, observers perceived isolated targets as only slightly tilted on error trials, and had little confidence in their decision. When the target was embedded in distractors, however, they perceived it to be strongly tilted on error trials, and had high confidence of their (erroneous) decisions. The results are well explained by assuming that the observers' internal representation of stimulus orientation arises from a nonlinear combination of the outputs of independent noise-perturbed front-end detectors. The implication that erroneous perceptual decisions in cluttered environments are made with high confidence has many potential practical consequences, and may be extendable to decision-making in general.

Multisensory interactions follow the hands across the midline: Evidence from a non-spatial visual–tactile congruency task

Crossing the hands over, whether across the body midline or with respect to each other, leads to measurable changes in spatial compatibility, spatial attention, and frequently to a general decrement in discrimination performance for tactile stimuli. The majority of multisensory crossed hands effects, however, have been demonstrated with explicit or implicit spatial discrimination tasks, raising the question of whether non-spatial discrimination tasks also show spatial effects when the hands are crossed. We designed a novel, non-spatial tactile discrimination task to address this issue. Participants made speeded discriminations of single- versus double-pulse vibrotactile targets, while trying to ignore simultaneous visual distractor stimuli, in both hands uncrossed and hands crossed postures. Tactile discrimination performance was significantly affected by the visual distractors (demonstrating a significant crossmodal congruency effect) and was affected most by visual distractors in the same external location as the tactile target (i.e., spatial modulation), regardless of the posture (uncrossed or crossed) of the hands (i.e., spatial ‘remapping’ of visual–tactile interactions). Finally, crossing the hands led to a general performance decrement with visual distractors, but not in a control task with unimodal visual or tactile judgements. These results demonstrate, for the first time, significant spatial and postural modulations of crossmodal congruency effects in a non-spatial discrimination task.

Brain Systems Mediating Cognitive Interference by Emotional Distraction

Flexible behavior depends on our ability to cope with distracting stimuli that can interfere with the attainment of goals. Emotional distracters can be particularly disruptive to goal-oriented behavior, but the neural systems through which these detrimental effects are mediated are not known. We used event-related functional magnetic resonance imaging to investigate the effect of emotional and nonemotional distracters on a delayed-response working memory (WM) task. As expected, this task evoked robust activity during the delay period in typical WM regions (dorsolateral prefrontal cortex and lateral parietal cortex). Presentation of emotional distracters during the delay interval evoked strong activity in typical emotional processing regions (amygdala and ventrolateral prefrontal cortex) while simultaneously evoking relative deactivation of the WM regions and impairing WM performance. These results provide the first direct evidence that the detrimental effect of emotional distracters on ongoing cognitive processes entails the interaction between a dorsal neural system associated with "cold" executive processing and a ventral system associated with "hot" emotional processing.

Combining Correlation and Interference Methods in the Human Brain. Focus on “Cortico-Cortical Interactions in Spatial Attention: A Combined ERP/TMS Study”

Recent years have witnessed an advance in the understanding and measurement of the neural correlates of attention in the human brain. For example, it is established that the allocation of attention is accompanied by changes in event related electrical potentials (ERPs) that can be recorded at the

Time sharing in rats: A peak-interval procedure with gaps and distracters

Four hypotheses (switch, instructional-ambiguity, memory decay, and time sharing) were evaluated in a reversed peak-interval procedure with gaps by presenting distracter stimuli during the uninterrupted timed signal. The switch, instructional-ambiguity, and memory-decay hypotheses predict that subjects should time through the distracter and delay responding during gaps. The time-sharing hypothesis assumes that the internal clock shares attentional and working-memory resources with other processes, so that both gaps and distracters delay timing by causing working memory to decay. We found that response functions were displaced both by gaps and by distracters. Computer simulations show that when combined, the memory-decay and time-sharing hypotheses can mechanistically address present data, suggesting that these two hypotheses may reflect different levels of analysis of the same phenomenon.