N2pc Component Research Articles

The different roles of category- and feature-specific attentional control settings on attentional enhancement and inhibition.

Contingent attentional capture suggests that top-down attentional control settings (ACS) can enhance attentional processing of task-relevant properties and inhibit attentional processing of task-irrelevant properties. However, it remains unclear how ACS operates when a distractor has both task-relevant and task-irrelevant characteristics. In the present study, two lateralized ERP components, N2pc and distractor positivity (Pd), were employed as markers of attentional enhancement and inhibition, respectively. The degree of matching between a distractor and a conjunctively defined target was manipulated to illustrate attentional guidance by category-specific ACS (cACS) and feature-specific ACS (fACS), and the relative position between the distractor and the target was manipulated to isolate the processing of the distractor and the target. Experiment 1 showed that, with a long display duration for searching, a reliable N2pc component was elicited by a distractor that was feature-matched but category-mismatched (C-F+) relative to the target-defined properties, suggesting an enhancing effect of fACS. In contrast, Experiment 2 demonstrated that, with a short display duration, a Pd component was elicited by a distractor that was feature-mismatched but category-matched (C+F-) relative to the target-defined properties, suggesting an inhibitory effect of fACS. Moreover, both attentional enhancement and inhibition were only triggered by fACS but not by cACS. In summary, ACS can enhance target-relevant properties or inhibit target-irrelevant properties in response to the display duration, and fACS affects both enhancement and inhibition more than cACS.

The Allocation of Attention in Change Detection and Change Blindness

Abstract. Visual change detection often fails when observers’ attention is distracted by some other visual disruptions in the environment that occur simultaneously with the change. This phenomenon is called change blindness. It has been claimed that selective attention is necessary for successful change detection. In the current experiment, two mechanisms of attention allocation in such a task were investigated. First, the number of distracting stimuli was varied to distract observers’ attention and, second, possible change positions were highlighted to allow observers to better focus on potential change locations. The N2pc component of the event-related potential was measured as an indicator of attentional selection. The results show that the sensitivity for changes increased either when observers were less distracted or when they were able to better focus their attention. However, these two mechanisms were reflected differently by the N2pc component. When observers’ attention was less distracted by a lower number of mudsplashes, the N2pc component occurred earlier. In contrast, when observers were able to better focus their attention on potential change locations, the N2pc component not only occurred earlier but also showed an additional enhancement in amplitude. That is, successful change detection depends on both, the properties of distracting and of changing objects. They determine the speed and intensity of the allocation of attention toward a change.

SELECTIVE ATTENTION IN AGE-ASSOCIATED MEMORY IMPAIRMENT: AN ERP STUDY IN VISUAL SEARCH

AbstractAge-Associated memory impairment (AAMI) may be related to a decline in selective attention. In this work, the potential attentional capture by task-irrelevant stimuli was examined in older adults with AAMI compared to healthy older adults using event-related potentials (ERPs).A visual search task was employed, in which the participants had to detect the presence of a target stimulus that differed from distractors by orientation. To explore the automatic attentional capture, an irrelevant distractor stimulus defined by color was also presented without previous knowledge of the subjects. The N2pc component of ERPs, an electrophysiological indicator of the allocation of attentional resources, was analysed.The results indicated that in both groups the N2pc component was present for target stimuli but not for task-irrelevant color stimuli. In addition, the latency of N2pc for targets was significantly delayed in AAMI patients compared to controls, although no differences in the amplitude of the component were found.The delay in N2pc latency in AAMI subjects suggested they require more time than healthy seniors to shift their visuospatial attention onto the task-relevant information. However, the lack of significant differences between the groups in N2pc mean amplitude and scalp distribution suggested that the amount of attentional resources allocated to the target did not differ between older adult with and without memory impairment. The lack of N2pc component for irrelevant non-target stimuli indicated that the mechanism of top-down suppression of task-irrelevant information is preserved.Funding: Xunta de Galicia (GPC2014/082)

Electroencephalographic theta oscillatory dynamics reveal attentional bias to angry faces.

Although previous studies have reported the temporal neural dynamics (e.g., N2pc component) of threat-detection orientation for face-processing (e.g., the "anger superiority effect"), little is known about the neural oscillatory features of this phenomenon. Here, we extracted the event-related potentials and event-related oscillatory power dynamics from electroencephalographic data when participants performed a visual search task consisting of realistic angry, happy, and neutral facial expressions. We observed a shorter response time and a larger N2pc for angry faces than for happy faces, suggesting the existence of preferential processing for angry faces. Similarly, elevated theta synchronization was observed for angry faces compared to happy faces, while both angry and happy faces elicited heightened theta oscillatory activity on contralateral location of target face compared to ipsilateral location. Moreover, the theta oscillation difference negatively correlated with the amplitude of the N2pc difference. Our findings suggest that the occipital theta oscillation is engaged in the search advantage of angry facial expressions. Further, our results provide evidence that the theta oscillation may reflect the processing dynamics of threat-stimuli orientation in an ever-changing environment.

Evidence for an attentional component of inhibition of return in visual search.

Inhibition of return (IOR) is typically described as an inhibitory bias against returning attention to a recently attended location as a means of promoting efficient visual search. Most studies examining IOR, however, either do not use visual search paradigms or do not effectively isolate attentional processes, making it difficult to conclusively link IOR to a bias in attention. Here, we recorded ERPs during a simple visual search task designed to isolate the attentional component of IOR to examine whether an inhibitory bias of attention is observed and, if so, how it influences visual search behavior. Across successive visual search displays, we found evidence of both a broad, hemisphere-wide inhibitory bias of attention along with a focal, target location-specific facilitation. When the target appeared in the same visual hemifield in successive searches, responses were slower and the N2pc component was reduced, reflecting a bias of attention away from the previously attended side of space. When the target occurred at the same location in successive searches, responses were facilitated and the P1 component was enhanced, likely reflecting spatial priming of the target. These two effects are combined in the response times, leading to a reduction in the IOR effect for repeated target locations. Using ERPs, however, these two opposing effects can be isolated in time, demonstrating that the inhibitory biasing of attention still occurs even when response-time slowing is ameliorated by spatial priming.

How handedness influences perceptual and attentional processes during rapid serial visual presentation

Stimulus-driven orienting of visual attention is lateralized to the right hemisphere (RH). This lateralization has been studied in the dual-stream rapid serial visual presentation task (dual RSVP). In this task a second target (T2), hard to discern by being embedded in one of two lateral streams of rapidly changing distractors, is better identified on the left than on the right. This phenomenon is called the left visual field advantage (LVFA). Furthermore, in terms of event related potentials (ERPs), the N2pc component and visual evoked potentials (VEPs) are evoked earlier at the RH than at the left hemisphere (LH). All previous dual RSVP experiments were performed on right-handers. In the present study it was investigated how the LVFA and its neural correlates are modulated by handedness. To that end, the size of the LVFA and ERPs (VEPs and N2pc) were compared between right- and left-handers. VEPs were evoked earlier at the RH than the LH in right-handers but not in left-handers. Besides this effect, handedness modulated neither the size of the LVFA nor T2-evoked N2pc. Thus, the LVFA seems to be independent of handedness. Rather than for lateralization of attention, handedness might be relevant for lateralization of early visual perception processes.

Attentional selection predicts rapid automatized naming ability in Chinese-speaking children with ADHD

Children with attention-deficit/hyperactivity disorder (ADHD) are reported to have a significantly higher risk of showing reading difficulties or disorders. Here, we aimed to identify the relationship between electroencephalographic (EEG) marker of spatial attention and reading ability in Chinese children with ADHD. First, we demonstrated that rapid automatized naming (RAN) is a strong predictor of reading ability in Chinese-speaking children. Then, EEG data of 9-to 15-year-old children with ADHD (n = 38) and typically developing (TD) controls (n = 36) were collected while the children performed a classical visual search task. Children with ADHD showed slower RAN speed than TD children. For event-related potentials (ERPs), children with ADHD showed a reduced target-evoked N2pc component, which predicted their poorer RAN performance. However, in TD children the early occipital P1 amplitude was negatively correlated with their RAN performance. The correlation between decreased N2pc and poor RAN performance in children with ADHD suggests that their reading problems may in part be due to impaired attentional selection. In contrast, in TD children, development in early visual processing co-occurs with improvements in reading ability.

Backward masking interrupts spatial attention, slows downstream processing, and limits conscious perception.

The attentional blink (AB) is a difficulty in correctly processing a target when it follows one or more other targets after a short delay. When no backward mask is presented after the last critical target, there is no or little behavioral AB deficit. The mask plays an important role in limiting conscious access to target information. In this electrophysiological study, we tested the impact of masking on the deployment and engagement of attention by measuring the N2pc and P3 components in an RSVP paradigm. We found that the presence of a mask in an AB paradigm reduced the amplitude of the N2pc, P3a, and P3b components. In addition to reducing encoding in memory, masking also reduced the effectiveness of the deployment and engagement of attention on the last target. We discuss the role of these findings in the context of current masking, consciousness, and AB models.

Enhancing links between visual short term memory, visual attention and cognitive control processes through practice: An electrophysiological insight

The operation of attention on visible objects involves a sequence of cognitive processes. The current study firstly aimed to elucidate the effects of practice on neural mechanisms underlying attentional processes as measured with both behavioural and electrophysiological measures. Secondly, it aimed to identify any pattern in the relationship between Event-Related Potential (ERP) components which play a role in the operation of attention in vision. Twenty-seven participants took part in two recording sessions one week apart, performing an experimental paradigm which combined a match-to-sample task with a memory-guided efficient visual-search task within one trial sequence. Overall, practice decreased behavioural response times, increased accuracy, and modulated several ERP components that represent cognitive and neural processing stages. This neuromodulation through practice was also associated with an enhanced link between behavioural measures and ERP components and with an enhanced cortico-cortical interaction of functionally interconnected ERP components. Principal component analysis (PCA) of the ERP amplitude data revealed three components, having different rostro-caudal topographic representations. The first component included both the centro-parietal and parieto-occipital mismatch triggered negativity – involved in integration of visual representations of the target with current task-relevant representations stored in visual working memory – loaded with second negative posterior-bilateral (N2pb) component, involved in categorising specific pop-out target features. The second component comprised the amplitude of bilateral anterior P2 – related to detection of a specific pop-out feature – loaded with bilateral anterior N2, related to detection of conflicting features, and fronto-central mismatch triggered negativity. The third component included the parieto-occipital N1 – related to early neural responses to the stimulus array – which loaded with the second negative posterior-contralateral (N2pc) component, mediating the process of orienting and focusing covert attention on peripheral target features. We discussed these three components as representing different neurocognitive systems modulated with practice within which the input selection process operates.

The spatially global control of attentional target selection in visual search

ABSTRACTGlyn Humphreys and his co-workers have made numerous important theoretical and empirical contributions to research on visual search. They have introduced the concept of attentional target templates and investigated the nature of these templates and how they are involved in the control of search performance. In the experiments reported here, we investigated whether feature-specific search templates for particular colours can guide target selection independently for different regions of visual space. We employed behavioural and electrophysiological markers of attentional selection in tasks with targets defined by specific colour/location combinations. In Experiment 1, participants searched for pairs of colour targets in a particular spatial configuration (e.g., red in the upper and blue in the lower visual field). In Experiment 2, they searched for single colour-defined targets at specific locations (e.g., red on the left or blue on the right). Target displays were preceded by non-informative cues containing target-colour items at task-set matching or mismatching locations. Contingent attentional capture was observed only for matching cues. However, both matching and mismatching cues elicited identical N2pc components, indicating equivalent attentional capture. This shows that the rapid deployment of attention towards target features is spatially non-selective, and that selection of colour/location combinations occurs at later post-perceptual stages. This was further corroborated in search displays where targets were accompanied by target-colour distractors at nonmatching locations. Here, spatial biases towards the target emerged late and were strongly attenuated relative to displays without such distractors. These results demonstrate that attentional templates for target-defining features operate in a spatially-global fashion. Feature-based guidance of visual search cannot be restricted to particular locations even when this is required by the demands of an attentional selection task.

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 (4/8VM), 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.

The N2pc component reliably captures attentional bias in social anxiety.

We systematically compared different measures of attentional bias (i.e., reaction times, the N2pc component in the EEG, and explicit stimulus ratings) on their ability to reveal attentional engagement to threatening versus neutral facial stimuli in a Dot Probe Task and tested their relation to trait measures of general and social anxiety. We found that the N2pc component reflects a bias toward angry faces with excellent internal consistency. Similar results were obtained for explicit ratings. Reaction time (RT) differences, however, were not indicative of attentional biases and showed zero odd-even reliability. We further found that both higher (i.e., more negative) N2pc amplitudes and earlier peak latencies were associated with more severe symptoms of social anxiety even when controlling for general trait anxiety. The explicit rating biases were also specifically associated with social anxiety. Conversely, the RT bias was not related to social anxiety levels but to general trait anxiety. This highlights the importance of valid and reliable outcome measures for interventions such as attentional bias modification protocols. Mutual exclusivity of different bias operationalizations is discussed.

Signal enhancement, not active suppression, follows the contingent capture of visual attention.

Irrelevant visual cues capture attention when they possess a task-relevant feature. Electrophysiologically, this contingent capture of attention is evidenced by the N2pc component of the visual event-related potential (ERP) and an enlarged ERP positivity over the occipital hemisphere contralateral to the cued location. The N2pc reflects an early stage of attentional selection, but presently it is unclear what the contralateral ERP positivity reflects. One hypothesis is that it reflects the perceptual enhancement of the cued search-array item; another hypothesis is that it is time-locked to the preceding cue display and reflects active suppression of the cue itself. Here, we varied the time interval between a cue display and a subsequent target display to evaluate these competing hypotheses. The results demonstrated that the contralateral ERP positivity is tightly time-locked to the appearance of the search display rather than the cue display, thereby supporting the perceptual enhancement hypothesis and disconfirming the cue-suppression hypothesis. (PsycINFO Database Record

Lateralized electrical brain activity reveals covert attention allocation during speaking

Speakers usually begin to speak while only part of the utterance has been planned. Earlier work has shown that speech planning processes are reflected in speakers’ eye movements as they describe visually presented objects. However, to-be-named objects can be processed to some extent before they have been fixated upon, presumably because attention can be allocated to objects covertly, without moving the eyes. The present study investigated whether EEG could track speakers’ covert attention allocation as they produced short utterances to describe pairs of objects (e.g., “dog and chair”). The processing difficulty of each object was varied by presenting it in upright orientation (easy) or in upside down orientation (difficult). Background squares flickered at different frequencies in order to elicit steady-state visual evoked potentials (SSVEPs). The N2pc component, associated with the focusing of attention on an item, was detectable not only prior to speech onset, but also during speaking. The time course of the N2pc showed that attention shifted to each object in the order of mention prior to speech onset. Furthermore, greater processing difficulty increased the time speakers spent attending to each object. This demonstrates that the N2pc can track covert attention allocation in a naming task. In addition, an effect of processing difficulty at around 200–350ms after stimulus onset revealed early attention allocation to the second to-be-named object. The flickering backgrounds elicited SSVEPs, but SSVEP amplitude was not influenced by processing difficulty. These results help complete the picture of the coordination of visual information uptake and motor output during speaking.

A temporal dependency account of attentional inhibition in oculomotor control

We used concurrent electroencephalogram (EEG) and eye tracking to investigate the role of covert attentional mechanisms in the control of oculomotor behavior. Human participants made speeded saccades to targets that were presented alongside salient distractors. By subsequently sorting trials based on whether the distractor was strongly represented or suppressed by the visual system – as evident in the accuracy (Exp. 1) or quality of the saccade (Exp. 2) – we could characterize and contrast pre-saccadic neural activity as a function of whether oculomotor control was established. Results show that saccadic behavior is strongly linked to the operation of attentional mechanisms in visual cortex. In Experiment 1, accurate saccades were preceded by attentional selection of the target – indexed by a target-elicited N2pc component – and by attentional suppression of the distractor – indexed by early and late distractor-elicited distractor positivity (Pd) components. In Experiment 2, the strength of distractor suppression predicted the degree to which the path of slower saccades would deviate away from the distractor en route to the target. However, results also demonstrated clear dissociations of covert and overt selective control, with saccadic latency in particular showing no relationship to the latency of covert selective mechanisms. Eye movements could thus be initiated prior to the onset of attentional ERP components, resulting in stimulus-driven behaviour. Taken together, the results indicate that attentional mechanisms play a role in determining saccadic behavior, but that saccade timing is not contingent on the deployment of attention. This creates a temporal dependency, whereby attention fosters oculomotor control only when attentional mechanisms are given sufficient opportunity to impact stimuli representations before an eye movement is executed.

Rapid Parallel Attentional Selection Can Be Controlled by Shape and Alphanumerical Category.

Previous research has shown that when two color-defined target objects appear in rapid succession at different locations, attention is deployed independently and in parallel to both targets. This study investigated whether this rapid simultaneous attentional target selection mechanism can also be employed in tasks where targets are defined by a different visual feature (shape) or when alphanumerical category is the target selection attribute. Two displays that both contained a target and a nontarget object on opposite sides were presented successively, and the SOA between the two displays was 100, 50, 20, or 10 msec in different blocks. N2pc components were recorded to both targets as a temporal marker of their attentional selection. When observers searched for shape-defined targets (Experiment 1), N2pc components to the two targets were equal in size and overlapped in time when the SOA between the two displays was short, reflecting two parallel shape-guided target selection processes with their own independent time course. Essentially the same temporal pattern of N2pc components was observed when alphanumerical category was the target-defining attribute (Experiment 2), demonstrating that the rapid parallel attentional selection of multiple target objects is not restricted to situations where the deployment of attention can be guided by elementary visual features but that these processes can even be employed in category-based attentional selection tasks. These findings have important implications for our understanding of the cognitive and neural basis of top-down attentional control.

The Role of Color in Search Templates for Real-world Target Objects.

During visual search, target representations (attentional templates) control the allocation of attention to template-matching objects. The activation of new attentional templates can be prompted by verbal or pictorial target specifications. We measured the N2pc component of the ERP as a temporal marker of attentional target selection to determine the role of color signals in search templates for real-world search target objects that are set up in response to word or picture cues. On each trial run, a word cue (e.g., "apple") was followed by three search displays that contained the cued target object among three distractors. The selection of the first target was based on the word cue only, whereas selection of the two subsequent targets could be controlled by templates set up after the first visual presentation of the target (picture cue). In different trial runs, search displays either contained objects in their natural colors or monochromatic objects. These two display types were presented in different blocks (Experiment 1) or in random order within each block (Experiment 2). RTs were faster, and target N2pc components emerged earlier for the second and third display of each trial run relative to the first display, demonstrating that pictures are more effective than word cues in guiding search. N2pc components were triggered more rapidly for targets in the second and third display in trial runs with colored displays. This demonstrates that when visual target attributes are fully specified by picture cues, the additional presence of color signals in target templates facilitates the speed with which attention is allocated to template-matching objects. No such selection benefits for colored targets were found when search templates were set up in response to word cues. Experiment 2 showed that color templates activated by word cues can even impair the attentional selection of noncolored targets. Results provide new insights into the status of color during the guidance of visual search for real-world target objects. Color is a powerful guiding feature when the precise visual properties of these objects are known but seems to be less important when search targets are specified by word cues.

Rapid attentional selection processes operate independently and in parallel for multiple targets

The question whether multiple objects are selected serially or in parallel remains contentious. Previous studies employed the N2pc component as a marker of attentional selection to show that multiple selection processes can be activated concurrently. The present study demonstrates that the concurrent selection of multiple targets reflects genuinely parallel processing that is unaffected by whether or when an additional selection process is elicited simultaneously for another target. Experiment 1 showed that N2pc components triggered during the selection of a colour-defined target were not modulated by the presence versus absence of a second target that appeared in close temporal proximity. Experiment 2 revealed that the same rapid parallel selection processes were elicited regardless of whether two targets appeared simultaneously or in two successive displays. Results show that rapid attentional selection processes within the first 200ms after stimulus onset can be triggered in parallel for multiple objects in the visual field.

Category-based guidance of spatial attention during visual search for feature conjunctions.

The question whether alphanumerical category is involved in the control of attentional target selection during visual search remains a contentious issue. We tested whether category-based attentional mechanisms would guide the allocation of attention under conditions where targets were defined by a combination of alphanumerical category and a basic visual feature, and search displays could contain both targets and partially matching distractor objects. The N2pc component was used as an electrophysiological marker of attentional object selection in tasks where target objects were defined by a conjunction of color and category (Experiment 1) or shape and category (Experiment 2). Some search displays contained the target or a nontarget object that matched either the target color/shape or its category among 3 nonmatching distractors. In other displays, the target and a partially matching nontarget object appeared together. N2pc components were elicited not only by targets and by color- or shape-matching nontargets, but also by category-matching nontarget objects, even on trials where a target was present in the same display. On these trials, the summed N2pc components to the 2 types of partially matching nontargets were initially equal in size to the target N2pc, suggesting that attention was allocated simultaneously and independently to all objects with target-matching features during the early phase of attentional processing. Results demonstrate that alphanumerical category is a genuine guiding feature that can operate in parallel with color or shape information to control the deployment of attention during visual search. (PsycINFO Database Record

Gestalt Perceptual Organization of Visual Stimuli Captures Attention Automatically: Electrophysiological Evidence

The visual system leverages organizational regularities of perceptual elements to create meaningful representations of the world. One clear example of such function, which has been formalized in the Gestalt psychology principles, is the perceptual grouping of simple visual elements (e.g., lines and arcs) into unitary objects (e.g., forms and shapes). The present study sought to characterize automatic attentional capture and related cognitive processing of Gestalt-like visual stimuli at the psychophysiological level by using event-related potentials (ERPs). We measured ERPs during a simple visual reaction time task with bilateral presentations of physically matched elements with or without a Gestalt organization. Results showed that Gestalt (vs. non-Gestalt) stimuli are characterized by a larger N2pc together with enhanced ERP amplitudes of non-lateralized components (N1, N2, P3) starting around 150 ms post-stimulus onset. Thus, we conclude that Gestalt stimuli capture attention automatically and entail characteristic psychophysiological signatures at both early and late processing stages.HighlightsWe studied the neural signatures of the automatic processes of visual attention elicited by Gestalt stimuli. We found that a reliable early correlate of attentional capture turned out to be the N2pc component. Perceptual and cognitive processing of Gestalt stimuli is associated with larger N1, N2, and P3