The Temporal Dynamic Relationship Between Attention and Crowding: Electrophysiological Evidence From an Event-Related Potential Study

Visual crowding is the difficulty experienced in identifying a target flanked by other objects within the peripheral visual field. Despite extensive research conducted on this topic, the precise relationship between attention and crowding is still debatable. One perspective suggests that crowding is a bottom-up and pre-attentive process, while another suggests that crowding is top-down and attentional. A third perspective proposes that crowding is a combination of bottom-up and top-down processes. To address this debate, the current study manipulated the attention and distance between targets and flankers, while simultaneously measuring event-related potentials, in human participants. Results indicated that, compared to uncrowded targets, crowded targets elicited more negative frontal N1 and P2 activity and a less negative occipital N1 activity, regardless of whether targets were attended or unattended, and a more positive occipital P2 activity when they were attended. Furthermore, the crowded minus uncrowded difference amplitude was more negative over the frontal region and more positive over the occipital region when the targets were attended, compared to when they were unattended during the N1 and P2 stages. This suggests that crowding, a concept that originates from Gestalt grouping, occurs automatically and can be modulated by attention

Long‐term (statistically learnt) and short‐term (inter‐trial) distractor‐location effects arise at different pre‐ and post‐selective processing stages

A salient distractor interferes less with visual search if it appears at a location where it is likely to occur, referred to as distractor-location probability cueing. Conversely, if the current target appears at the same location as a distractor on the preceding trial, search is impeded. While these two location-specific “suppression” effects reflect long-term, statistically learnt and short-term, inter-trial adaptations of the system to distractors, it is unclear at what stage(s) of processing they arise. Here, we adopted the additional-singleton paradigm and examined lateralized event-related potentials (L-ERPs) and lateralized alpha (8–12 Hz) power to track the temporal dynamics of these effects. Behaviorally, we confirmed both effects: reaction times (RTs) interference was reduced for distractors at frequent versus rare (distractor) locations, and RTs were delayed for targets that appeared at previous distractor versus non-distractor locations. Electrophysiologically, the statistical-learning effect was not associated with lateralized alpha power during the pre-stimulus period. Rather, it was seen in an early N1pc referenced to the frequent distractor location (whether or not a distractor or a target occurred there), indicative of a learnt top-down prioritization of this location. This early top-down influence was systematically modulated by (competing) target- and distractor-generated bottom-up saliency signals in the display. In contrast, the inter-trial effect was reflected in an enhanced SPCN when the target was preceded by a distractor at its location. This suggests that establishing that an attentionally selected item is a task-relevant target, rather than an irrelevant distractor, is more demanding at a previously “rejected” distractor location

Il était une fois une cible et un distracteur : électrophysiologie des mécanismes corticaux de l'attention visuelle en perception et en mémoire

Cet ouvrage explore en trois volets des aspects du traitement attentionnel de cibles et de distracteurs visuels ainsi que leur mesures électrophysiologiques. Le premier chapitre aborde le traitement attentionnel spécifique à la cible et aux distracteurs durant une recherche visuelle. La division de la N2pc en une NT et une PD remet en question la théorie proposant qu'il existe systématiquement une activité attentionnelle liée à un distracteur saillant, car un distracteur vert ne provoque aucune activité latéralisée propre. Le second chapitre aborde la question de la latéralisation des structures responsables du maintient et de la récupération d'information en mémoire visuelle à court-terme. En utilisant un paradigme de latéralisation de la cible et du distracteur, il nous est possible de vérifier qu'il existe une composante latéralisée négative dans la région temporale, la TCN, propre à la cible lors du rappel en mémoire. De plus, on observe également une composante latéralisée pour le distracteur sur la partie postérieure du crâne. Ces deux éléments convergent pour indiquer qu'il existe une latéralisation des structures activées lors de la récupération de l'information en mémoire visuelle à court-terme en fonction de l'hémichamps où se trouve la cible ou le distracteur. Enfin, dans le troisième chapitre, il est question de l'effet sur le déploiement attentionnel de l'ajout de distracteurs gris de faible saillance autour de cibles potentielles. L'ajout de ces distracteurs augmente la difficulté d'identification de la cible. Cette difficulté provoque un déplacement de l'activité de la N2pc vers la fenêtre de temps associée à la composante Ptc. Un nombre plus important de distracteurs gris entraîne une plus grande proportion de l'activité à être retardée. Également, les distracteurs gris qui sont placés entre les cibles potentielles provoquent un retard plus important que les distracteurs placés hors de cette région. Au cours de cette thèse, la question de la saillance attentionnelle des différentes couleurs durant une recherche visuelle est récurente. Nous observons une plus grande saillance du rouge par rapport au vert quand ils sont distracteurs et le vert est plus difficile à distinguer du gris que le jaune.This thesis explore various aspects of attentional processing of visual targets and distractors as well as their electrophysiological expression. First, the opening chapter investigate target and distractor specific attentional processing during a visual search task. Splitting the N2pc into an NT and a PD allows us to reject the hypothesis that all salliant distractors require an attentionnal processing, since no distractor-specific lateralized activity can be observed for a lateral green distractor. After then, during the second chapter, we separate target and distractor specific activity during VSTM retrieval to explore the lateralization of memory structures. We identified a temporal lateralized negative component, the TCN, which is solely related to the retrieval of the target from VSTM. We also found a posterior distractor-related positive component. Both components suggest a lateralized activation of structures during VSTM retrieval related to the encoding hemisphere during perception. Then finally, during the third chapter, despite the absence of systematic attentional processing, we explore the effect of low salience distractors on attentional deployment during a visual search task. Inserting grey distractors around color potential targets increases the difficulty to individuate the potential targets and lead to attentional deployment delay. Increasing the number of grey distractors lead to an increased proportion of N2pc activity being delayed into the following Ptc time-window. Also, more delayed activity can be observed when grey distractors are placed between the potential targets instead of outside this region. Across this thesis, we also address the attentional salience of color as a recurent source of attentional imbalance. Red generate distractor-specific lateralized activity, while green do not and green is harder to individuate with surrounding grey distractors compared to yellow

Exploring the Powers of Mindfulness-Based Training on Enhanced Executive Function and Improved Response Accuracy

Humans are flooded with a large number of visual stimuli at any waking moment, and to act efficiently, we filter information based on how relevant it is to us and avoid stimuli that may be considered distracting. Research has demonstrated that those who meditate have improved executive functioning compared to controls, however observing the mechanisms behind these improvements, needs further exploration. Visual event-related potentials (ERPs) can be used to assess visual selective attention. Specifically, in response to lateralized attended stimuli the N2pc (posterior contralateral) is associated with top-down attentional selection and the distractor positivity (Pd) with lateralized distractor suppression. Through using these visual ERPs, we were able to explore the mechanisms behind improved visual attention that we see in experienced meditators specifically the lateralization of target selection and suppression. We hypothesized that those who have been meditating consistently can draw their attention more efficiently towards a target, represented by a larger N2pc, and suppressing distractors, represented by a larger Pd. Additionally, we hypothesized that the meditators would respond more accurately than controls and would have a reduction in interference post-error indicated by a larger error-related negativity (ERN). Electroencephalography (EEG) was collected from 28 participants (15 control, 13 meditators; 19-31 years). Meditators had to be meditating for at least the past year with an average of 45 minutes spent in meditation each week. ERPs were measured using EEG to investigate cognitive processing using a modified flanker task where two sets of three-letter arrays were arranged vertically on either side of a white fixation cross, one green array, the other red. Participants were instructed to indicate whether the middle letter of the attended array (red/green) was a consonant or a vowel via keypad. Participants were instructed to attend to either array across 10 blocks (5 attend-green; 5 attend-red) with 100 trials presented per block for a total of 1000 trials. N2pc and Pd were extracted from correct trials only via subtracting contralateral-ipsilateral electrodes (P3/4 and P7/8) relative to the attended target or distractor for the N2pc and Pd, respectively. ERPs were quantified via mean wave amplitude over a time window of 200-300ms (N2pc) and 300-400ms (Pd) after stimulus onset. ERN was extracted by subtracting correct from incorrect trials and taking the peak negative amplitude within 0-150ms after response onset at the Cz site. Response time (latency) was recorded, and accuracy was measured via correct vs error trials (excluding missed trials). Results showed that on average meditators had larger N2pc and Pd components, however, the two-way mixed ANOVAs for the N2pc and Pd did not reveal a significant difference between meditators and a control group regarding the size of the N2pc or Pd component, however the there is a strong possibility of a type II error regarding the N2pc. The effect size for the N2pc indicated practical significance and we may have been underpowered in detecting this significance due to a small sample size. On average meditators were more accurate, however we failed to detect a statistical improvement between the two groups, similarly to the N2pc, the effect sizes regarding accuracy suggest practical significance and that the current lack of statistical significance may be misleading. However, we did find a significant effect of colour in both accuracy and latency revealing that regardless of group, participants were more accurate and had a faster response on attend-green trials. Although ERP data reveal no significance regarding the effect of colour, there was a trend present where in meditators the Pd amplitude was larger in attend-green versus attend-red trials. Suggesting that this effect of colour on accuracy and latency is due to distractor suppression, not target selection. Additionally, there was a main effect of time for both the N2pc and Pd components, participants experienced attentional fatigue in the form a reduced activity directed towards suppressing distractors and attending to targets in the form of a smaller Pd and N2pc, respectively. Overall, on average those who had been meditating for at least a year experienced larger N2pc and Pd components compared to a control, however a statistical significance was not reached as a result of being underpowered in conducting these tests

Motivation and visual attention in adolescents and adults

This thesis explores how the motivation to process a visual stimulus influences attentional control. A core aim was to develop and test a motivation-based as opposed to a perception-based explanation for reward association effects on visual selective attention. To do so, in a series of 12 experiments, stimuli were first imbued with a value, reinforced with monetary wins and losses. Then, these same value-associated stimuli were used as distractors in spatial attention paradigms, including flanker and visual search tasks, incentive cues in a simple detection task, or targets in an ensemble perceptual judgment task. Of primary interest were measures of attentional capture by value-laden opposed to neutral stimuli. Taking a developmental approach, in a subset of the experiments value-driven biases in late adolescents compared to adults were also examined while simultaneous electroencephalography was recorded. Collectively, the results from these experiments suggest that the effects of motivational salience are inconsistent with perception-based accounts but can be encompassed in a motivation-based framework that suggests value-associated stimuli compete to alter current goals. This motivation-based model is grounded in the cognitive control literature and posits a competition among potential goals driven by the costs versus benefits of cognitive engagement with stimuli

NEURAL CHRONOMETRY OF VISUAL ATTENTION & THREAT PROCESSING

Most anxiety disorders in adults emerge during adolescence, and if left untreated, pediatric anxiety disorders predict adverse mental and physical health outcomes in adolescents and adults. While genetic heritability is a contributing risk factor, a heightened tendency to direct attention preferentially to threat represents one of the strongest information-processing correlates of anxiety; such an attention bias may shape both the development and maintenance of anxiety symptoms. Attentional performance differences have been observed on emotion cueing visual attention tasks as a function of both clinical and sub-clinical anxiety levels. Previous work in adults observed that for adults with higher anxiety symptoms, efficiency of visual search was degraded by threat-cueing faces. However, further work is required to clarify the emergence attentional biases in adolescents, to inform methods for early identification, intervention and treatment of individuals at risk for anxiety. The present study examined the impact of emotional priming on attention as a function of anxiety using a task in which emotional faces were used as primes for a visual search task. Event Related Potentials (ERP) (P1, N170 and N2pc) were recorded in concert with behavioral responses to address the chronometry and quality of attentional processing as a function of anxiety symptoms in adolescents, 12-17 years of age. Early P1 and N170 processing in the first few hundred milliseconds of viewing face primes, differed as a function of both anxiety and prime emotion. Moreover, these anxiety-related early processing differences related to subsequent behavior. Variability in the N2pc attention-related processing during visual search also varied as a function of anxiety and prime type, as well as affected subsequent behavior. This dissertation found both early and later occurring attentional processes have significant ramifications for individuals with higher anxiety scores, such that in addition to neural differences, high anxious individuals also display significant differences in behavior. While early and late neural processes varied in lower anxious individuals as a function of face prime type, relations with behavior were minimal in comparison. These findings are discussed as they relate to emotion processing, threat responsivity to facial stimuli, and applicability to pediatric and adult clinical anxiety

The interplay between attention, working memory, and linked neural signatures in visual tracking and inhibition

The aims of this thesis began with investigating whether inattentional blindness was associated with a propensity for lower sensitivity to semantic violations in image textures. Inattentional blindness has recently been investigated through methods such as manipulation of low-level image statistics in artificial textures. However, work in this thesis aimed to transition such research into more natural contexts. Whilst a variety of methods were explored, results specifically related to inattentional blindness and working memory capacity remained inconclusive. Therefore, work in this thesis moved from investigating differences across inattentional blindness groups to how potential strategies of object tracking and relationships to working memory capacity can influence tracking performance. Results from the first half of this thesis provide novel insights into methods that can help to investigate sensitivity to distractors in a naturalistic setting, with both behavioural and neural data. This shift away from investigating inattentional blindness to patterns of tracking across working memory capacity also coincided with a shift to linear mixed effects modelling. This allowed the thesis to remove any artificial grouping through median scores of capacities, and instead focus more on sensitivity across the spectrum. Over five tracking studies, a number of findings suggest of differences across working memory capacity can compensate in performance for such capacity limitations. Findings also suggest that participants, regardless of capacity, employ a post-probe approximation estimation when tracking targets over a trial gap, as opposed to active tracking. Results from the tracking studies emphasise the differing approaches that individuals with varying working memory employ when tracking multiple and single objects

The Allocation of Attention and Working Memory in Visual Crowding

When the distance between a visual target and nearby flankers falls below a critical distance, target discrimination declines precipitously. This is called "crowding." Many researchers have proposed that selective attention plays a role in crowding. However, although some research has examined the effects of directing attention toward versus away from the targets, no previous research has assessed how attentional allocation varies as a function of target-flanker distance in crowding. Here, we used ERPs to assess the operation of attention during crowding, focusing on the attention-related N2pc component. We used a typical crowding task in which participants were asked to report the category (vowel/consonant) of a lateralized target letter flanked by distractor letters at different distances. We tested the hypothesis that attention fails when the target-flanker distance becomes too small for attention to operate effectively. Consistent with this hypothesis, we found that N2pc amplitude was maximal at intermediate target-flanker distances and decreased substantially when crowding became severe. In addition, we examined the sustained posterior contralateral negativity (SPCN), which reflects the amount of information being maintained in working memory. Unlike the N2pc component, the SPCN increased in amplitude at small target-flanker distances, suggesting that observers stored information about the target and flankers in working memory when attention failed to select the target. Together, the N2pc and SPCN results suggest that attention and working memory play distinctive roles in crowding: Attention operates to minimize interference from the flankers at intermediate target-flanker distances, whereas working memory may be recruited when attention fails to select the target at small target-flanker distances