Proactive suppression can be applied to multiple salient distractors in visual search.

There is a growing body of research demonstrating that the capture of attention by a single salient distractor can be prevented via proactive suppression. In real-world contexts, there are often several distracting events that compete for attention, but it is entirely unknown whether multiple objects can be suppressed concurrently. We used behavioral and electrophysiological measures to investigate the existence and time course of multiple-item suppression. We employed search displays that contained either one or two uniquely colored distractors that differed in their salience (S+ and S-), or no such distractors. Search performance improved with the number of salient distractors, indicating that the suppression of multiple items reduced the effective display set size. This was also the case when the target color was no longer fully predictable, ruling out an alternative explanation in terms of attentional guidance by target templates. In an experiment where S+ and S- always appeared together in the same display, the PD component (a marker of proactive suppression) was triggered exclusively by the more salient distractor (S+), indicative of single-item suppression. However, when displays with one or both salient distractors were intermixed, a reliable PD component was also triggered by S-, even when it was accompanied by S+ in the same display. These results show that multiple concurrent salient signals can be proactively inhibited. They demonstrate that signal suppression processes can be adaptively employed to counteract visual distraction at different locations, in order to facilitate the attentional selection of relevant objects in crowded visual environments. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Task-irrelevant filler items alter the dynamics of electrical brain activity during visual search.

In electroencephalography (EEG) studies of visual search, task-irrelevant fillers are included in displays to balance bottom-up stimulation across the visual field and generally considered as inconsequential for performance or EEG results. We examined the impact of fillers on target and distractor processing using lateralised event-related potentials (ERPs). Two task-relevant items (TRIs) were presented, with or without fillers. One TRI (target or target-colour distractor) was on the vertical midline and the other in a lateral position (left or right visual field) on an imaginary circle around fixation. An N2pc was elicited by lateral targets and task-relevant distractors, suggesting that attention was allocated to the lateral TRI because it possessed a target defining feature (colour). A Ptc was only elicited by lateral task-relevant distractors, in line with previous research suggesting that this component is associated with distractor processing. When fillers were also in the circular arrangement, alterations in performance and neural activity occurred. Fillers enhanced and delayed attentional deployment (N2pc) and delayed distractor processing (Ptc). Critically, we observed no difference in Ptc amplitude according to filler presence. Thus, if the Ptc reflects active suppression (or attentional disengagement), it was not required for fillers. ERPs were also modulated by the distance between TRIs (which could be separated by one or four filler positions), but differently according to the colour scheme (blue TRIs with grey fillers or vice versa). Our results suggest that fillers affect lateralised electrophysiological activity at multiple loci during visual search and should not be considered inconsequential.

On target selection as reflected by posterior ERP components in feature-guided visual search.

The N2pc event-related potential is a widely studied ERP component that reflects the covert deployment of visuo-spatial attention to target stimuli displayed laterally relative to fixation. Recently, an analogous ERP component, named N2pcb, has been proposed as a marker of the deployment of visuo-spatial attention to targets displayed on the vertical midline. Two studies that investigated the N2pcb component found analogous results, using however two different algorithms to compute the amplitude of N2pcb. One study subtracted the ipsilateral activity elicited by a lateral target from the bilateral activity elicited by a target displayed on the vertical midline, whereas the other study subtracted the bilateral activity elicited by target-absent displays from the bilateral activity elicited by a target displayed on the vertical midline. Here we show both algorithms estimate properly the N2pc as well as the N2pcb components. In addition, we explored whether the singleton detection positivity (SDP) component, a posterior bilateral positivity temporally concomitant to N2pc recently reported in studies using singleton search, could be observed in the present study in which a target was defined by a combination of features. Given that such component was indeed found using feature search, we named this component posterior processing positivity (PPP), and showed that bilateral activity elicited by target-absent displays is an adequate baseline for its correct isolation.

PD components and distractor inhibition in visual search: New evidence for the signal suppression hypothesis.

The hypothesis that salient distractors in visual search are actively suppressed is supported by the fact that these objects elicit PD components believed to be associated with inhibition. This account was challenged by researchers who found that a PD to lateral color singleton distractors was followed by a contralateral negativity, which they interpreted as an N2pc indicative of attentional capture. As this would be at odds with successful distractor suppression, they proposed an alternative lateral-first serial scanning hypothesis, which assumes that the PD might actually be an N2pc elicited when a lateral context item is selected. We tested this hypothesis by measuring lateralized ERP components to search displays with two lateral and two vertical midline items, including a color singleton and a shape-defined target. Color singletons triggered PD components not only in blocks where attention was unfocused because target location was unpredictable, but critically also in blocks where targets only appeared on the midline and participants had no reason to attend to lateral items. This is inconsistent with the serial scanning hypothesis and supports the idea that the PD reflects signal suppression. PD components to singleton distractors were followed by a contralateral negativity, which we interpreted as a second PD elicited by nonsalient distractors on the opposite side. Our sequential inhibition account reconciles conflicting results of recent studies and emphasizes the role of inhibitory processes during attentional target selection in visual search.

Interhemispheric differences in P1 and N1 amplitude in EEG and MEG differ across older individuals with a concussion compared with age-matched controls.

We studied the effects of mild traumatic brain injury (mTBI) in an aging population. We examined visual search with event-related potentials (ERPs) and event-related fields (ERF) for a lateral color singleton focusing on the P1 and N1 in each hemisphere. Forty participants (19 mTBI and 21 controls) aged 50 to 72 performed a visual search task, while we recorded their magnetoencephalogram (MEG) with simultaneous electroencephalogram (EEG). We compared visual ERPs and ERFs and associated cortical activity estimated using MEG source localization. Relative to matched controls, participants with an mTBI had a smaller P1 in the left hemisphere and a smaller N1 in the right hemisphere. Also, mTBI participants showed inversed activation patterns across the hemispheres during the N1 in MEG compared with controls. This is the first study to investigate the impact of mTBI on neuronal source activations during early visual processing in an aging population. Results showed that when aging individuals suffer from an mTBI, there are perturbations in the amplitude and hemispheric dominance patterns in the visual P1 and N1 responses that are visible for months to years following the injury. Our findings indicate that mTBI can lead to modifications of sensory and/or perceptual responses, suggesting possible adaptive functional reorganization following mTBI.

Effects of task-irrelevant or filler items on brain mechanisms of visual spatial attention.

Many visual search paradigms use color to distinguish task-relevant items from those considered fillers (e.g., blue task-relevant items and grey fillers). Hilimire and colleagues suggested that the N2pc, a lateralized electrophysiological component typically observed in visual attention, is a neural correlate for localized attentional interference, which postulates that target selection is degraded by nearby competing stimuli. In their study, N2pc amplitude decreased with decreasing distance between task-relevant items presented among fillers. With an increase in distance, however, there was also an increase in the number of fillers between task-relevant items. We tested whether this distance effect could be explained by the presence of fillers near task-relevant items rather than their proximity per se. We manipulated the distance between task-relevant items (adjacent, separated by two, or by four positions) and the presence/absence of fillers orthogonally. We used two color schemes: blue task-relevant items and grey fillers or grey task-relevant items and blue fillers (manipulated between-subjects) to control for color interactions. N2pc amplitude increased with increasing distance, but only when fillers were present, suggesting that the results of Hilimire et al. may be due to increasing fillers interference. Exploratory analyses also suggested that the colors selected to be task-relevant and task-irrelevant could play a role in our ability to filter task-irrelevant information. Our results suggest that fillers are not as inconsequential as sometimes assumed and generally support the Ambiguity Resolution Theory, where nearby items increase N2pc amplitude because of a greater need for focused attention.

Dissecting Cognitive Operations in Difficult Visual Search Using Response-locked Posterior Contralateral Negativity Event-related Potentials.

We bisected the sequence of processing into operations taking place before or after the engagement of visual-spatial attention during a difficult search task using event-related potentials. We were able to assign variance in RTs associated with experimental factor effects to phases of processing by examining stimulus-locked (SLpcN) and response-locked (RLpcN) posterior contralateral negativity. Participants searched for a gray square with one gap among gray squares with two gaps. The number of displayed items (set size) and the number of response alternatives were varied. Both experimental manipulations affected the onset latency of the RLpcN, whereas the SLpcN showed small or no latency effects, suggesting they had effects after the initial deployment of attention. Moreover, amplitude effects in the RLpcN and SLpcN behaved similarly. Most importantly, different aspects of the RLpcN dissociated the experimental manipulations: Set size primarily affected processing between RLpcN onset and peak amplitude of the RLpcN, whereas the number of response alternatives affected the onset latency and the latency of peak amplitude of RLpcN. These results show how RLpcN activity can dissociate factor effects that are not separable with SLpcN activity during difficult search.

Stimulus- and Response-locked Posterior Contralateral Negativity Bisect Cognitive Operations in Visual Search.

We explored the flow of information during visual search by examining activity indexing visual attention (N2pc) and the subsequent processing of the selected objects in visual short-term memory (SPCN) time-locked to stimulus presentation and to the motor response. We measured event-related activity at posterior sites (PO7/PO8) for 96 participants during a simple visual search task. A response-locked posterior contralateral negativity (RLpcN) was observed with a scalp distribution similar to that of the N2pc and SPCN. The RLpcN was compared with the stimulus-locked activity (N2pc and SPCN) across experimental manipulations (targets were either closer or farther from fixation in visual space, and the response was either more frequent [75%] or less frequent [25%]) and across response speeds (EEG data were separated into tertiles by RT both within-subjects and between-subjects). The leading edge and early portion of the RLpcN appeared to reflect the initial deployment of attention (N2pc), whereas the later portion (up to peak amplitude) reflected subsequent processing of visual information (SPCN). SPCN and RLpcN also had similar modulations in amplitude for both analyses. Moreover, whereas very small N2pc and SPCN onset latency differences were observed when data were separated into tertiles by RT, there were large onset differences for the RLpcN, with earlier RLpcN onsets for longer RTs, suggesting that RT variance is in large determined by processing after the initial deployment of attention. The results show how we can bisect processing responsible for variations in RT relative to the onset of visual spatial attention.

Early and late selection processes have separable influences on the neural substrates of attention.

To improve our understanding of the mechanisms of target selection, we examined how the spatial separation of salient items and their similarity to a pre-defined target interact using lateralised electrophysiological correlates of visual spatial attention (N2pc component) and visual short-term memory (VSTM; SPCN component). Using these features of target selection, we sought to expand on previous work proposing a model of early and late selection, where the N2pc is suggested to reflect the selection probability of visual stimuli (Aubin and Jolicoeur, 2016). The authors suggested that early-selection processes could be enhanced when items are adjacent. In the present work, the stimuli were short oriented lines, all of which were grey except for two that were blue and hence salient. A decrease in N2pc amplitude with decreasing spatial separation between salient items was observed. The N2pc increased in amplitude with increasing similarity of salient distractors to the target template, but only in target-absent trials. There was no interaction between these two factors, suggesting that separable attentional mechanisms influenced the N2pc. The findings suggest that selection is initially based on easily-distinguished attributes (i.e., both blue items) followed by a later identification-based process (if necessary), which depends on feature similarity to a target template. For the SPCN component, the results were in line with previous work: for target-present trials, an increase in similarity of salient distractors was associated with an increase in SPCN amplitude, suggesting more information was maintained in VSTM. In sum, results suggest there is a need for further inspection of salient distractors when they are similar to the target, increasing the need for focal attention, demonstrated by an increase in N2pc amplitude, followed by a higher probability of transfer to VSTM, demonstrated by an increase in SPCN amplitude.

Electrophysiological impact of multiple concussions in asymptomatic athletes: A re-analysis based on alpha activity during a visual-spatial attention task.

Most EEG studies used event-related potentials to assess long-term and cumulative effects of sport-related concussions on brain activity. Time-frequency methods provide another approach that allows the detection of subtle shifts in types and patterns of brain oscillations. We sought to discover whether event-related alpha activity would be significantly affected in asymptomatic multi-concussed athletes. We measured the amplitude of alpha activity (8-12Hz) from the EEG recorded during a visual-spatial attention task to compare event-related alpha perturbations in 13 multi-concussed athletes and 14 age-equivalent, non-concussed teammates. Relative to non-concussed athletes, multi-concussed athletes showed significantly less event-related perturbations time-locked to stimulus presentation. Alpha activity alterations were closely related to the number of concussions sustained. Event-related alpha activity differed in asymptomatic multi-concussed athletes when compared to controls. Our study suggests that low-level neurophysiological underpinnings of the deployment of visual-spatial attention are affected in multi-concussed athletes even though their last concussion occurred on average 30 months prior to testing.

Electrophysiological evidence for enhanced attentional deployment in spatial learners.

Visual spatial attention is important during navigation processes that rely on a cognitive map, because spatial relationships between environmental landmarks need to be selected, encoded, and learned. People who navigate using this strategy are spatial learners, and this process relies on the hippocampus. Conversely, response learners memorize a series of actions to navigate, which relies on the caudate nucleus. Response learning, which is more efficient, is thought to involve less demanding cognitive operations, and is related to reduced grey matter in the hippocampus. To test if navigational strategy can impact visual attention performance, we investigated if spatial and response learners showed differences in attentional engagement used during a visual spatial task. We tested 40 response learners and 39 spatial learners, as determined by the 4-on-8 Virtual Maze (4/8 VM), on a target detection task designed to elicit an N2pc component (an index visual spatial attention). Spatial learners produced a larger N2pc amplitude during target detection compared to response learners. This relationship might represent an increase in goal-directed attention towards target stimuli or a more global increase in cognitive function that has been previously observed in spatial learners.

Dealing with ocular artifacts on lateralized ERPs in studies of visual-spatial attention and memory: ICA correction versus epoch rejection.

The objective of the present study was to assess the robustness and reliability of independent component analysis (ICA) as a method for ocular artifact correction in electrophysiological studies of visual-spatial attention and memory. The N2pc and sustained posterior contralateral negativity (SPCN), electrophysiological markers of visual-spatial attention and memory, respectively, are lateralized posterior ERPs typically observed following the presentation of lateral stimuli (targets and distractors) along with instructions to maintain fixation on the center of the visual search for the entire trial. Traditionally, trials in which subjects may have displaced their gaze are rejected based on a cutoff threshold, minimizing electrophysiological contamination by saccades. Given the loss of data resulting from rejection, we examined ocular correction by comparing results using standard fixation instructions against a condition where subjects were instructed to shift their gaze toward possible targets. Both conditions were analyzed using a rejection threshold and ICA correction for saccade activity management. Results demonstrate that ICA conserves data that would have otherwise been removed and leaves the underlying neural activity intact, as demonstrated by experimental manipulations previously shown to modulate the N2pc and the SPCN. Not only does ICA salvage and not distort data, but also large eye movements had only subtle effects. Overall, the findings provide convincing evidence for ICA correction for not only special cases (e.g., subjects did not follow fixation instruction) but also as a candidate for standard ocular artifact management in electrophysiological studies interested in visual-spatial attention and memory.

Habitual action video game playing is associated with caudate nucleus-dependent navigational strategies.

The habitual playing of video games is associated with increased grey matter and activity in the striatum. Studies in humans and rodents have shown an inverse relationship between grey matter in the striatum and hippocampus. We investigated whether action video game playing is also associated with increased use of response learning strategies during navigation, known to be dependent on the caudate nucleus of the striatum, when presented in a dual solution task. We tested 26 action video game players (actionVGPs) and 33 non-action video game players (nonVGPs) on the 4-on-8 virtual maze and a visual attention event-related potential (ERP) task, which elicits a robust N-2-posterior-controlateral (N2pc) component. We found that actionVGPs had a significantly higher likelihood of using a response learning strategy (80.76%) compared to nonVGPs (42.42%). Consistent with previous evidence, actionVGPs and nonVGPs differed in the way they deployed visual attention to central and peripheral targets as observed in the elicited N2pc component during an ERP visual attention task. Increased use of the response strategy in actionVGPs is consistent with previously observed increases in striatal volume in video game players (VGPs). Using response strategies is associated with decreased grey matter in the hippocampus. Previous studies have shown that decreased volume in the hippocampus precedes the onset of many neurological and psychiatric disorders. If actionVGPs have lower grey matter in the hippocampus, as response learners normally do, then these individuals could be at increased risk of developing neurological and psychiatric disorders during their lifetime.

The perception of concurrent sound objects through the use of harmonic enhancement: a study of auditory attention.

When the frequency of one harmonic, in a sound composed of many harmonics, is briefly mistuned and then returned to the 'in-tune' frequency and phase, observers report hearing this harmonic as a separate tone long after the brief period of mistuning - a phenomenon called harmonic enhancement. Here, we examined the consequence of harmonic enhancement on listeners' ability to detect a brief amplitude notch embedded in one of the harmonics after the period of mistuning. When present, the notch was either on the enhanced harmonic or on a different harmonic. Detection was better on the enhanced harmonic than on a non-enhanced harmonic. This finding suggests that attention was drawn to the enhanced harmonic (which constituted a new sound object) thereby easing the processing of sound features (i.e., a notch) within that object. This is the first evidence of a functional consequence of the after-effect of transient mistuning on auditory perception. Moreover, the findings provide support for an attention-based explanation of the enhancement phenomenon.