Revisiting the automaticity of reading: Electrophysiological recordings show that stroop words capture spatial attention

Interference in the Stroop task is reduced when the word and color patch are placed at different locations and is diluted further by the presence of another distractor that is response neutral. Such dilution indicates that reading is not independent of an observer's attentional focus and thus is not a fully automatic process. So where does reading fall on the automaticity continuum? To address this question, we sought to determine whether an irrelevant word that appears abruptly in the field of view invariably draws attention to its location or whether observers can successfully ignore it while identifying a centrally presented target. In two experiments, electrical brain activity was recorded while healthy young adults participated in nonintegrated Stroop tasks. Irrelevant color words appearing randomly to the left or right of a target shape elicited an event-related potential component that reflects the spatial focusing of attention (posterior contralateral N2; N2pc). This N2pc was observed when participants discriminated the color of the target and when they discriminated the shape of the target. These findings demonstrate that color words reflexively capture spatial attention even when their meaning is unrelated to the task at hand. We conclude that although reading is not fully automatic, skilled readers cannot ignore words that appear abruptly in their field of view. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Attentional enhancement predicts individual differences in visual working memory under go/no-go search conditions

Attention-control processes transfer relevant information to visual working memory (WM) and prevent irrelevant information from consuming WM resources. Although event-related potentials (ERPs) have revealed attention-control processes associated with enhancement of relevant stimuli (targets) and suppression of irrelevant stimuli (distractors), only the suppressive processes have been found to predict WM capacity. We hypothesised a link between target-enhancement processes and WM capacity would be revealed in a task that requires more control than the conventional visual search paradigms used to study target selection. Here, participants searched for a pop-out target on Go trials and withheld responses on an equal number of randomly intermixed No-Go trials, depending on the colour of the stimulus array. Magnitudes of ERP indices associated with target enhancement (the singleton detection positivity, SDP, and N2pc) were positively correlated with individual differences in WM capacity. These relationships vanished when participants searched for the pop-out target on every trial, regardless of stimulus-array colour. Inhibitory processes associated with suppressing distractors (PD) and withholding responses (no-go P3) on No-Go trials did not predict WM capacity. These findings indicate that target-enhancement mechanisms control access to WM in search tasks that require dynamic control and disconfirm the view that the gateway to WM is entirely inhibitory by nature.

Searching for Visual Singletons Without A Feature to Guide Attention

RT studies have provided evidence for a singleton-detection strategy that is used to search for salient targets when there is no additional featural knowledge that would help guide attention. Despite this behavioral evidence, there have been few ERP studies of singleton detection mode because it was reported early on that the ERP signature of attentional selection (the N2pc) is absent without feature guidance. Recently, however, it was discovered that a small and relatively late N2pc occurs in singleton detection mode along with a previously unreported component called the singleton detection positivity (SDP). Here, we show that both components are influenced by the number of items in the display, as one might expect in a salience-based search mode. Specifically, the N2pc and SDP were larger when the set size was increased to make the singleton "pop out" more easily, when participants responded more quickly regardless of set size, and when RT search slopes were negative (Experiment 1). The latency of the SDP also depended on set size. In Experiment 2, EEG was recorded with a higher density electrode array to better characterize the scalp topography of the components and to estimate their neural sources. Regional sources near the ventral surface of extrastriate cortex in the occipital lobe explained over 96% of N2pc and SDP activities. These results indicate that searching in singleton detection mode selectively modulates processing within perceptual regions of visual cortex.

Diversion of Attention Leads to Conflict between Concurrently Attended Stimuli, Not Delayed Orienting to the Object of Interest

The control processes that guide attention to a visual-search target can result in the selection of an irrelevant object with similar features (a distractor). Once attention is captured by such a distractor, search for a subsequent target is momentarily impaired if the two stimuli appear at different locations. The textbook explanation for this impairment is based on the notion of an indivisible focus of attention that moves to the distractor, illuminates a nontarget that subsequently appears at that location, and then moves to the target once the nontarget is rejected. Here, we show that such delayed orienting to the target does not underlie the behavioral cost of distraction. Observers identified a color-defined target appearing within the second of two stimulus arrays. The first array contained irrelevant items, including one that shared the target's color. ERPs were examined to test two predictions stemming from the textbook serial-orienting hypothesis. Namely, when the target and distractor appear at different locations, (1) the target should elicit delayed selection activity relative to same-location trials, and (2) the nontarget search item appearing at the distractor location should elicit selection activity that precedes selection activity tied to the target. Here, the posterior contralateral N2 component was used to track selection of each of these search-array items and the previous distractor. The results supported neither prediction above, thereby disconfirming the serial-orienting hypothesis. Overall, the results show that the behavioral costs of distraction are caused by perceptual and postperceptual competition between concurrently attended target and nontarget stimuli.

Recoiling from Threat: Anxiety is Related to Heightened Suppression of Threat, Not Increased Attention to Threat

Increased attention to threat is considered a core feature of anxiety. However, there are multiple mechanisms of attention and multiple types of threat, and the relationships among attention, threat, and anxiety are poorly understood. The present study used event-related potentials (ERPs) to separately isolate attentional selection (N2pc) and suppression (P_D) of pictorial threats (photos of weapons, snakes, etc.) and conditioned threats (colored shapes paired with electric shock). In a sample of 48 young adults, both threat types were initially selected for increased attention (an N2pc), but only conditioned threats elicited subsequent suppression (a P_D) and a reaction time (RT) bias. Levels of trait anxiety were unrelated to N2pc amplitude, but increased anxiety was associated with larger P_Ds (i.e., greater suppression) and reduced RT bias to conditioned threats. These results suggest that anxious individuals do not pay more attention to threats, but rather engage more attentional suppression to overcome threats.

Circadian misalignment impairs ability to suppress visual distractions

Evening-type individuals often perform poorly in the morning because of a mismatch between internal circadian time and external social time, a condition recognized as social jet lag. Performance impairments near the morning circadian (~24 hr) trough have been attributed to deficits in attention, but the nature of the impairment is unknown. Using electrophysiological indices of attentional selection (N2pc) and suppression (P_D ), we show that evening-type individuals have a specific disability in suppressing irrelevant visual distractions. More specifically, evening-type individuals managed to suppress a salient distractor in an afternoon testing session, as evidenced by a P_D , but were less able to suppress the distractor in a morning testing session, as evidenced by an attenuated P_D and a concomitant distractor-elicited N2pc. Morning chronotypes, who would be well past their circadian trough at the time of testing, did not show this deficit at either test time. These results indicate that failure to filter out irrelevant stimuli at an early stage of perceptual processing contributes to impaired cognitive functioning at nonoptimal times of day and may underlie real-world performance impairments, such as distracted driving, that have been associated with circadian mismatch.

From alternation to repetition: Spatial attention biases contribute to sequential effects in a choice reaction-time task

Observers often take longer to respond to a visual target when it appears at a recently stimulated location than when it appears at a new location in the visual field. This behavioral impairment - known as inhibition of return (IOR) - is mirrored by a reduction of an event-related potential (ERP) component called the N2pc that has been associated with attentional selection. Together, these findings indicate that the mechanism underlying IOR operates to bias covert attention against re-visiting the most recently attended location. The goal of the present study was to determine how this inhibitory attention bias evolves across successive trials of a two-item search task. Initially, targets appearing at previously attended locations were associated with behavioral IOR and a concomitant reduction of the N2pc. After several successive trials, this initial inhibitory bias was superseded by expectancy-based biases associated with "predictable" inter-trial patterns of location repeats or location changes, in some cases leading to faster responses and a larger N2pc when the target location repeated (facilitation of return).  These results provide evidence that biases in the covert deployment of attention are updated dynamically according to the recent selection history and contribute to well-known sequential effects in serial choice reaction-time tasks.

Electrophysiological correlates of visual singleton detection

Identifying a fixed-feature singleton that pops out from an otherwise uniform array of distractors elicits an ERP component called the N2pc over the posterior scalp. The N2pc has been used to track attention with millisecond accuracy, inform theories of visual selection, and test for specific attention deficits in clinical populations, yet it is still unclear what neuro-cognitive process gives rise to the component. One hypothesis is that the N2pc reflects a spatial filtering process that suppresses irrelevant distractors. In support of this hypothesis, Luck and Hillyard (1994a) showed that the N2pc is eliminated when the features of the target and distractors switch unpredictably across trials (so that participants cannot prepare to filter out irrelevant items). The present study aimed to replicate Luck and Hillyard's singleton detection experiment but with modifications to enhance the N2pc signal and to gain statistical power. We show that orientation singletons do, in fact, elicit the N2pc as well as an earlier-onset and longer-lasting singleton detection positivity over the occipital scalp when the target and distractor orientations swap randomly across trials. We conclude that spatial filtering might not play a major role in the generation of the N2pc and that the selection processes required to search for fixed-feature targets (in feature-search mode) are also engaged in the detection of variable-feature singletons (in singleton detection mode).

High Level of Trait Anxiety Leads to Salience-Driven Distraction and Compensation

Individuals with high levels of anxiety are hypothesized to have impaired executive control functions that would otherwise enable efficient filtering of irrelevant information. Pinpointing specific deficits is difficult, however, because anxious individuals may compensate for deficient control functions by allocating greater effort. Here, we used event-related-potential indices of attentional selection (the N2pc) and suppression (the PD) to determine whether high trait anxiety is associated with a deficit in preventing the misallocation of attention to salient, but irrelevant, visual search distractors. Like their low-anxiety counterparts ( n = 19), highly anxious individuals ( n = 19) were able to suppress the distractor, as evidenced by the presence of a PD. Critically, however, the distractor was found to trigger an earlier N2pc in the high-anxiety group but not in the low-anxiety group. These findings indicate that, whereas individuals with low anxiety can prevent distraction in a proactive fashion, anxious individuals deal with distractors only after they have diverted attention.

Social media engagement amongst 2017 colorectal surgery Tripartite Meeting attendees: updates on contemporary social media use

AIM

Engagement by medical professionals with social media (SM) is increasing. Variation is noted in engagement between SM platforms and between surgical specialities and geographical regions. We aimed to study SM engagement by colorectal surgeons attending an international conference.

METHOD

Surgeons were identified from the delegate list of the 2017 Annual Meeting of the American Society of Colon and Rectal Surgeons (ASCRS) and Tripartite Meeting (Seattle, Washington, USA). Delegates were searched on Twitter and LinkedIn for the presence of a matching profile. SM presence, activity, gender and geographical region were analysed.

RESULTS

Two hundred and seventy (13.2%) surgeons had Twitter accounts and 994 (44.3%) had LinkedIn profiles. UK surgeons were more likely to be on Twitter than surgeons from elsewhere (23.4% vs 12.7%, P = 0.0072). Significant variation in SM membership between each geographical region was noted, with usage rates for Twitter of 18.1% in Europe, 14.4% in North America, 12.9% in South America, 4.3% in Oceania, 3.7% in Asia and 0% in Africa. A similar picture for LinkedIn is seen. The #ASCRS17 meeting saw the highest participation of users to date (979 participants, over 7000 individual tweets and nearly 14 million impressions).

CONCLUSION

SM engagement by colorectal surgeons continues to increase. Significant geographical variation is noted, suggesting that SM's unique potential for education and networking may not yet be widely appreciated globally. Future work should include further analysis into tweet contents to gain insights and optimize the use of SM as an educational adjunct.

Electrophysiological evidence of an attentional bias in crossmodal inhibition of return

Inhibition of return (IOR) refers to a delay in responding to targets when they appear at recently attended locations, relative to unattended locations. Within the visual modality, this attentional bias has been associated with a reduction in the N2pc event-related potential (ERP) component at previously attended locations. The present study examined whether a similar attentional bias was observed in crossmodal audio-visual IOR. Our results demonstrate that for visual targets, the attentional component of IOR behaves similarly for both unimodal and crossmodal target pairs, as indexed by a reduction in the N2pc component for targets appearing at previously attended locations. Further, similar IOR-related modulations on the auditory-evoked N2ac indicated that an attentional bias can be observed for auditory targets as well. Finally, we identified two additional ERP components - the ACOP and VCAN - that appear to reflect biasing of attention in the currently unattended sensory modality. These results suggest that the inhibitory attentional bias that underlies the IOR effect may be supramodal and bias attention away from previously attended locations regardless of sensory modality.

Learning what matters: A neural explanation for the sparsity bias

The visual environment is filled with complex, multi-dimensional objects that vary in their value to an observer's current goals. When faced with multi-dimensional stimuli, humans may rely on biases to learn to select those objects that are most valuable to the task at hand. Here, we show that decision making in a complex task is guided by the sparsity bias: the focusing of attention on a subset of available features. Participants completed a gambling task in which they selected complex stimuli that varied randomly along three dimensions: shape, color, and texture. Each dimension comprised three features (e.g., color: red, green, yellow). Only one dimension was relevant in each block (e.g., color), and a randomly-chosen value ranking determined outcome probabilities (e.g., green > yellow > red). Participants were faster to respond to infrequent probe stimuli that appeared unexpectedly within stimuli that possessed a more valuable feature than to probes appearing within stimuli possessing a less valuable feature. Event-related brain potentials recorded during the task provided a neurophysiological explanation for sparsity as a learning-dependent increase in optimal attentional performance (as measured by the N2pc component of the human event-related potential) and a concomitant learning-dependent decrease in prediction errors (as measured by the feedback-elicited reward positivity). Together, our results suggest that the sparsity bias guides human reinforcement learning in complex environments.

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

Contemporary engagement with social media amongst hernia surgery specialists

PURPOSE

Healthcare professional engagement is increasing. This study aims to identify levels of adoption and engagement of several social media platforms by a large international cohort of hernia surgery specialists.

METHODS

Hernia specialists attending the 38th International Congress of the European Hernia Society were identified. A manual search was then performed on Twitter, ResearchGate, and LinkedIn to identify those who had named accounts. Where accounts were identified, data on markers of utilisation were assessed.

RESULTS

759 surgeons (88.5% male) from 57 countries were identified. 334 surgeons (44%) engaged with a social media platform. 39 (5.1%) had Twitter accounts, 189 (24.9%) had ResearchGate accounts and 265 (34.9%) had LinkedIn accounts. 137 surgeons (18.1%) had accounts on 2 or more social media platforms. There was no gender association with social media account ownership (p > 0.05). Engagement in one social media platform was associated with increased engagement and utilisation on other platforms; LinkedIn users were more likely to have Twitter accounts (p < 0.001) and ResearchGate profiles (p < 0.001). Surgeons on all three SM platforms were more likely to have high markers of engagement across all SM platforms (multiple outcomes, p < 0.05). Geographical variation was noted with UK and South American Surgeons being more likely to be present on Twitter than their counterparts (p = 0.031).

CONCLUSIONS

The level of engagement with social media amongst Hernia surgeons is similar to other surgical specialities. Geographical variation in SM engagement is seen. Engagement with one SM platform is associated with presence on multiple platforms.

In vitro Sequential Selection and Characterization of Human Immunodeficiency Virus Type 1 Variants with Reduced Sensitivity to Hydroxyethylurea Protease Inhibitors

In vitro resistance to the human immunodeficiency virus (HIV) protease inhibitors SC-52151 and SC-55389A was evaluated in an in vitro sequential selection scheme. HIVRF variants were selected for reduced sensitivity to SC-52151 and subsequently passaged in both SC-52151 and a structurally different hydroxyethylurea protease inhibitor, SC-55389A, to select for dual-resistant virus. SC-52151 selection alone resulted in a 23-fold reduction in virus sensitivity whereas selection in both inhibitors resulted in 34- and eightfold reductions in virus sensitivity to SC-52151 and SC-55389A, respectively. Sequence analysis of the protease gene revealed that SC-52151 -resistant virus had a Gly to Val substitution at residue 48 (G48V) and, in 58% of subclones, an accompanying Val to Ala substitution at residue 82 (V82A). Dual-resistant virus had both G48V and V82A substitutions present and, in the majority of subclones, an lle to Thr and/or Leu to Pro substitution at residues 54 and 63, respectively. Drug susceptibility assays with limiting dilution-cloned HIVRFR (G48V/V82A) and HIVRFRR (G48V/154T/L63P/V82A) viruses demonstrated moderate to high-level cross-resistance to additional structurally non-related protease inhibitors. Recombinant HIVHXB2 proviral clones with G48V, L63P and V82A substitutions showed that one active site mutation was permissible, but the presence of both G48V and V82A substitutions together significantly reduced infectious virus production. Insight into the contributions of the observed substitutions to drug resistance is presented in molecular modelling studies.

Inability to suppress salient distractors predicts low visual working memory capacity

According to contemporary accounts of visual working memory (vWM), the ability to efficiently filter relevant from irrelevant information contributes to an individual's overall vWM capacity. Although there is mounting evidence for this hypothesis, very little is known about the precise filtering mechanism responsible for controlling access to vWM and for differentiating low- and high-capacity individuals. Theoretically, the inefficient filtering observed in low-capacity individuals might be specifically linked to problems enhancing relevant items, suppressing irrelevant items, or both. To find out, we recorded neurophysiological activity associated with attentional selection and active suppression during a competitive visual search task. We show that high-capacity individuals actively suppress salient distractors, whereas low-capacity individuals are unable to suppress salient distractors in time to prevent those items from capturing attention. These results demonstrate that individual differences in vWM capacity are associated with the timing of a specific attentional control operation that suppresses processing of salient but irrelevant visual objects and restricts their access to higher stages of visual processing.

Salient, Irrelevant Sounds Reflexively Induce Alpha Rhythm Desynchronization in Parallel with Slow Potential Shifts in Visual Cortex

Recent findings suggest that a salient, irrelevant sound attracts attention to its location involuntarily and facilitates processing of a colocalized visual event [McDonald, J. J., Störmer, V. S., Martinez, A., Feng, W. F., & Hillyard, S. A. Salient sounds activate human visual cortex automatically. Journal of Neuroscience, 33, 9194–9201, 2013]. Associated with this cross-modal facilitation is a sound-evoked slow potential over the contralateral visual cortex termed the auditory-evoked contralateral occipital positivity (ACOP). Here, we further tested the hypothesis that a salient sound captures visual attention involuntarily by examining sound-evoked modulations of the occipital alpha rhythm, which has been strongly associated with visual attention. In two purely auditory experiments, lateralized irrelevant sounds triggered a bilateral desynchronization of occipital alpha-band activity (10–14 Hz) that was more pronounced in the hemisphere contralateral to the sound's location. The timing of the contralateral alpha-band desynchronization overlapped with that of the ACOP (∼240–400 msec), and both measures of neural activity were estimated to arise from neural generators in the ventral-occipital cortex. The magnitude of the lateralized alpha desynchronization was correlated with ACOP amplitude on a trial-by-trial basis and between participants, suggesting that they arise from or are dependent on a common neural mechanism. These results support the hypothesis that the sound-induced alpha desynchronization and ACOP both reflect the involuntary cross-modal orienting of spatial attention to the sound's location.

Searching for inefficiency in visual search

The time required to find an object of interest in the visual field often increases as a function of the number of items present. This increase or inefficiency was originally interpreted as evidence for the serial allocation of attention to potential target items, but controversy has ensued for decades. We investigated this issue by recording ERPs from humans searching for a target in displays containing several differently colored items. Search inefficiency was ascribed not to serial search but to the time required to selectively process the target once found. Additionally, less time was required for the target to "pop out" from the rest of the display when the color of the target repeated across trials. These findings indicate that task relevance can cause otherwise inconspicuous items to pop out and highlight the need for direct neurophysiological measures when investigating the causes of search inefficiency.

Contemporary use of social media by consultant colorectal surgeons

AIM

There is evidence of significant growth in the engagement of UK health-care professionals with 'open' social media platforms, such as Twitter and LinkedIn. Social media communication provides many opportunities and benefits for medical education and interaction with patients and colleagues. This study was undertaken to evaluate the uptake of public social media membership and the characteristics of use of such media channels amongst contemporary UK consultant colorectal surgeons.

METHOD

Colorectal surgeons were identified from the Association of Coloproctology of Great Britain and Ireland (ACPGBI) national registry of colorectal mortality outcomes and were cross-referenced with the General Medical Council (GMC) register. Individuals were identified by manual searching on a number of social media platforms. Matching accounts were then examined to confirm ownership and to evaluate key markers of use.

RESULTS

Six-hundred and eighteen individual consultant colorectal surgeons from 142 health authorities were studied (79.5% were ACPGBI members and 90.8% were male). Two-hundred and twenty-nine (37.1%) had LinkedIn profiles (37.7% male surgeons, 29.8% female surgeons; P = 0.2530). LinkedIn membership was significantly higher in ACPGBI members (P < 0.001) and in those with GMC registration before 1997 vs after this date (39% before 1997 vs 30% after 1997; P = 0.03). LinkedIn members had a mean of 62 connections (median = 22), and 19 (3.1%) surgeons had Twitter profiles with a mean of 82 (median = 16; range: 0-914) followers and their accounts were followed by a mean of 87 (median = 27; range: 0-642) persons.

CONCLUSION

UK consultant colorectal surgeons are less engaged with social media than reported studies from other health-care professional groups. Further education and appropriate guidance on usage may encourage uptake and confidence, particularly in younger consultants.

The attentional blink freezes spatial attention allocation to targets, not distractors: evidence from human electrophysiology

Previous work found a significant reduction of the amplitude of the N2pc ERP component during the attentional blink in response to lateral visual targets, suggesting that the allocation of attention to visual targets is impaired during the attentional blink. Recent theorizing on the processes reflected by the N2pc suggests the possibility of distinct sets of neural mechanisms underlying its generation, one responsible for target activation, and one for distractor inhibition. To disentangle whether either or both of these mechanisms are impaired during the attentional blink, an RSVP sequence of circles, equidistant from fixation was used. The first target frame (T1) contained the same repeated target colour circle and target whereas the second target frame (T2) contained a distractor colour singleton as well as a target colour singleton. Only the target or only the distractor was presented at a lateral position; the other singleton was presented on the vertical midline so as not to elicit any event-related lateralization. Impaired T2 report accuracy at a short stimulus-onset asynchrony (SOA) was accompanied by a significant delay of the N2pc to lateral T2 targets when compared to a long SOA condition. No such delay was found when the lateralized stimulus was a distractor, suggesting that the attentional blink impacts attention allocation to targets, not distractors. We also observed a lateralized component earlier than the N2pc, a posterior contralateral positivity (Ppc) that did not depend on T1-T2 SOA and that was elicited by both lateral targets and distractors. We conclude that, contrary to N2pc, the Ppc likely reflects activity of bottom-up mechanisms responding unselectively to asymmetrical visual displays.

Tracking target and distractor processing in fixed-feature visual search: evidence from human electrophysiology

Salient distractors delay visual search for less salient targets in additional-singleton tasks, even when the features of the stimuli are fixed across trials. According to the salience-driven selection hypothesis, this delay is due to an initial attentional deployment to the distractor. Recent event-related potential (ERP) studies found no evidence for salience-driven selection in fixed-feature search, but the methods employed were not optimized to isolate distractor ERP components such as the N2pc and distractor positivity (PD; indices of selection and suppression, respectively). Here, we isolated target and distractor ERPs in two fixed-feature search experiments. Participants searched for a shape singleton in the presence of a more-salient color singleton (Experiment 1) or for a color singleton in the presence of a less-salient shape singleton (Experiment 2). The salient distractor did not elicit an N2pc, but it did elicit a PD on fast-response trials. Furthermore, distractors had no effect on the timing of the target N2pc. These results indicate that (a) the distractor was prevented from engaging the attentional mechanism associated with N2pc, (b) the distractor did not interrupt the deployment of attention to the target, and (c) competition for attention can be resolved by suppressing locations of irrelevant items on a salience-based priority map.

On the electrophysiological evidence for the capture of visual attention

The presence of a salient distractor interferes with visual search. According to the salience-driven selection hypothesis, this interference is because of an initial deployment of attention to the distractor. Three event-related potential (ERP) findings have been regarded as evidence for this hypothesis: (a) salient distractors were found to elicit an ERP component called N2pc, which reflects attentional selection; (b) with target and distractor on opposite sides, a distractor N2pc was reported to precede the target N2pc (N2pc flip); (c) the distractor N2pc on slow-response trials was reported to occur particularly early, suggesting that the fastest shifts of attention were driven by salience. This evidence is equivocal, however, because the ERPs were noisy (b, c) and were averaged across all trials, thereby making it difficult to know whether attention was deployed directly to the target on some trials (a, b). We reevaluated this evidence using a larger sample size to reduce noise and by analyzing ERPs separately for fast- and slow-response trials. On fast-response trials, the distractor elicited a contralateral positivity (PD)-an index of attentional suppression-instead of an N2pc. There was no N2pc flip or early distractor N2pc. As it stands, then, there is no ERP evidence for the salience-driven selection hypothesis.

The role of temporal predictability in the anticipatory biasing of sensory cortex during visuospatial shifts of attention

The presentation of an attention-directing cue elicits a lateralized ERP deflection called the late directing attention positivity (LDAP) and lateralized changes in alpha-band elelctroencephalogram oscillations. Both of these electrophysiological responses have been independently linked to biasing of visual cortex in anticipation of an impending target. However, the LDAP is not always observed, and the link between the ERP and alpha-band modulations remains unclear. Here, we examined the effect of advance knowledge of the time of target onset on the ERP and alpha-band responses to cues. The LDAP was present only when the attention-directing cues accurately indicated the time of target appearance, whereas two sequential attention-related alpha-band modulations were observed regardless of the temporal information provided by the cues. Thus, alpha-band activity may be a more reliable index of pretarget biasing of visual cortical activity than lateralized ERP effects.

Rhythms of consciousness: binocular rivalry reveals large-scale oscillatory network dynamics mediating visual perception

Consciousness has been proposed to emerge from functionally integrated large-scale ensembles of gamma-synchronous neural populations that form and dissolve at a frequency in the theta band. We propose that discrete moments of perceptual experience are implemented by transient gamma-band synchronization of relevant cortical regions, and that disintegration and reintegration of these assemblies is time-locked to ongoing theta oscillations. In support of this hypothesis we provide evidence that (1) perceptual switching during binocular rivalry is time-locked to gamma-band synchronizations which recur at a theta rate, indicating that the onset of new conscious percepts coincides with the emergence of a new gamma-synchronous assembly that is locked to an ongoing theta rhythm; (2) localization of the generators of these gamma rhythms reveals recurrent prefrontal and parietal sources; (3) theta modulation of gamma-band synchronization is observed between and within the activated brain regions. These results suggest that ongoing theta-modulated-gamma mechanisms periodically reintegrate a large-scale prefrontal-parietal network critical for perceptual experience. Moreover, activation and network inclusion of inferior temporal cortex and motor cortex uniquely occurs on the cycle immediately preceding responses signaling perceptual switching. This suggests that the essential prefrontal-parietal oscillatory network is expanded to include additional cortical regions relevant to tasks and perceptions furnishing consciousness at that moment, in this case image processing and response initiation, and that these activations occur within a time frame consistent with the notion that conscious processes directly affect behaviour.

Inhibition of Return in the Covert Deployment of Attention: Evidence from Human Electrophysiology

People are slow to react to objects that appear at recently attended locations. This delay—known as inhibition of return (IOR)—is believed to aid search of the visual environment by discouraging inspection of recently inspected objects. However, after two decades of research, there is no evidence that IOR reflects an inhibition in the covert deployment of attention. Here, observers participated in a modified visual-search task that enabled us to measure IOR and an ERP component called the posterior contralateral N2 (N2pc) that reflects the covert deployment of attention. The N2pc was smaller when a target appeared at a recently attended location than when it appeared at a recently unattended location. This reduction was due to modulation of neural processing in the visual cortex and the right parietal lobe. Importantly, there was no evidence for a delay in the N2pc. We conclude that in our task, the inhibitory processes underlying IOR reduce the probability of shifting attention to recently attended locations but do not delay the covert deployment of attention itself.

Electrophysiological Indices of Target and Distractor Processing in Visual Search

Attentional selection of a target presented among distractors can be indexed with an event-related potential (ERP) component known as the N2pc. Theoretical interpretation of the N2pc has suggested that it reflects a fundamental mechanism of attention that shelters the cortical representation of targets by suppressing neural activity stemming from distractors. Results from fields other than human electrophysiology, however, suggest that attention does not act solely through distractor suppression; rather, it modulates the processing of both target and distractors. We conducted four ERP experiments designed to investigate whether the N2pc reflects multiple attentional mechanisms. Our goal was to reconcile ostensibly conflicting outcomes obtained in electrophysiological studies of attention with those obtained using other methodologies. Participants viewed visual search arrays containing one target and one distractor. In Experiments 1 through 3, the distractor was isoluminant with the background, and therefore, did not elicit early lateralized ERP activity. This work revealed a novel contralateral ERP component that appears to reflect direct suppression of the cortical representation of the distractor. We accordingly name this component the distractor positivity (PD). In Experiment 4, an ERP component associated with target processing was additionally isolated. We refer to this component as the target negativity (NT). We believe that the N2pc reflects the summation of the PD and NT, and that these discrete components may have been confounded in earlier electrophysiological studies. Overall, this study demonstrates that attention acts on both target and distractor representations, and that this can be indexed in the visual ERP.

Tracking the voluntary control of auditory spatial attention with event-related brain potentials

A lateralized event-related potential (ERP) component elicited by attention-directing cues (ADAN) has been linked to frontal-lobe control but is often absent when spatial attention is deployed in the auditory modality. Here, we tested the hypothesis that ERP activity associated with frontal-lobe control of auditory spatial attention is distributed bilaterally by comparing ERPs elicited by attention-directing cues and neutral cues in a unimodal auditory task. This revealed an initial ERP positivity over the anterior scalp and a later ERP negativity over the parietal scalp. Distributed source analysis indicated that the anterior positivity was generated primarily in bilateral prefrontal cortices, whereas the more posterior negativity was generated in parietal and temporal cortices. The anterior ERP positivity likely reflects frontal-lobe attentional control, whereas the subsequent ERP negativity likely reflects anticipatory biasing of activity in auditory cortex.

Performance monitoring in the anterior cingulate is not all error related: expectancy deviation and the representation of action-outcome associations

Several converging lines of evidence suggest that the anterior cingulate cortex (ACC) is selectively involved in error detection or evaluation of poor performance. Here we challenge this notion by presenting event-related potential (ERP) evidence that the feedback-elicited error-related negativity, an ERP component attributed to the ACC, can be elicited by positive feedback when a person is expecting negative feedback and vice versa. These results suggest that performance monitoring in the ACC is not limited to error processing. We propose that the ACC acts as part of a more general performance-monitoring system that is activated by violations in expectancy. Further, we propose that the common observation of increased ACC activity elicited by negative events could be explained by an overoptimistic bias in generating expectations of performance. These results could shed light into neurobehavioral disorders, such as depression and mania, associated with alterations in performance monitoring and also in judgments of self-related events.

Electrical Neuroimaging Reveals Timing of Attentional Control Activity in Human Brain

Voluntarily shifting attention to a location of the visual field improves the perception of events that occur there. Regions of frontal cortex are thought to provide the top-down control signal that initiates a shift of attention, but because of the temporal limitations of functional brain imaging, the timing and sequence of attentional-control operations remain unknown. We used a new analytical technique (beamformer spatial filtering) to reconstruct the anatomical sources of low-frequency brain waves in humans associated with attentional control across time. Following a signal to shift attention, control activity was seen in parietal cortex 100–200 ms before activity was seen in frontal cortex. Parietal cortex was then reactivated prior to anticipatory biasing of activity in occipital cortex. The magnitudes of early parietal activations were strongly predictive of the degree of attentional improvement in perceptual performance. These results show that parietal cortex, not frontal cortex, provides the initial signals to shift attention and indicate that top-down attentional control is not purely top down.

To extract important details about objects in the environment, people must focus their attention on a specific location in space at any given moment. Research using functional magnetic resonance imaging (fMRI) has suggested that regions of the frontal and parietal lobes work together to control our ability to direct attention to a specific location in space in preparation for an expected visual object. However, the sluggishness of the hemodynamic response has made it difficult to obtain information from fMRI about the timing of activity. Electroencephalography (EEG) has provided information about the timing of neural activity, but the limitations of traditional source estimation techniques have made it difficult to obtain information about the precise location in the brain that the EEG signals are coming from. Thus, the sequence of activities within this frontal-parietal network remains unclear. We used a recently developed electrical neuroimaging technique—called beamforming—to localize the neural generators of low-frequency electroencephalographic (EEG) signals, which enabled us to determine both the location and temporal sequence of activations in the brain during shifts of visuospatial attention. Our results indicate that low-frequency signals in parietal cortex provide the initial signal to shift attention.

Localization of low-frequency brain rhythms reveals that within the frontal-parietal attentional control network, the parietal lobes provide the initial signal to shift attention in space.

Lateralized frontal activity elicited by attention-directing visual and auditory cues

In event-related potential studies of voluntary spatial attention, lateralized activity observed over anterior scalp sites prior to an impending target has been interpreted as the activity of a supramodal attentional control mechanism in the frontal lobes. However, variability in the scalp topography and presence of this activity across studies suggests that multiple neural generators contribute to the lateralized activity recorded at the scalp. Using distributed source modeling we found two distinct frontal lobe sources following attention-directing cues, one dependent on the sensory modality of the eliciting stimulus and one dependent on the response requirements of the task. Differential activity of these sources depending on task parameters suggests that neither source reflects activity necessary for controlling attention.

An event-related potential study of supramodal attentional control and crossmodal attention effects

We conducted two audiovisual experiments to determine whether event-related potential (ERP) components elicited by attention-directing cues reflect supramodal attentional control. Symbolic visual cues were used to direct attention prior to auditory targets in Experiment 1, and symbolic auditory cues were used to direct attention prior to visual targets in Experiment 2. Different patterns of cue ERPs were found in the two experiments. A frontal negativity called the ADAN was absent in Experiment 2, which indicates that this component does not reflect supramodal attentional control. A posterior positivity called the LDAP was observed in both experiments but was focused more posteriorly over the occipital scalp in Experiment 2. This component appears to reflect multiple processes, including visual processes involved in location marking and target preparation as well as supramodal processes involved in attentional control.

Electrophysiological Evidence of the Capture of Visual Attention

We investigated the ability of salient yet task-irrelevant stimuli to capture attention in two visual search experiments. Participants were presented with circular search arrays that contained a highly salient distractor singleton defined by color and a less salient target singleton defined by form. A component of the event-related potential called the N2pc was used to track the allocation of attention to lateralized positions in the arrays. In Experiment 1, a lateralized distractor elicited an N2pc when a concurrent target was presented on the vertical meridian and thus could not elicit lateralized components such as the N2pc. A similar distractor-elicited N2pc was found in Experiment 2, which was conducted to rule out certain voluntary search strategies. Additionally, in Experiment 2 both the distractor and the target elicited the N2pc component when the two stimuli were presented on opposite sides of the search array. Critically, the distractor-elicited N2pc preceded the target-elicited N2pc on these trials. These results demonstrate that participants shifted attention to the target only after shifting attention to the more salient but task-irrelevant distractor. This pattern of results is in line with theories of attention in which stimulus-driven control plays an integral role.

Effects of spatial congruity on audio-visual multimodal integration

Spatial constraints on multisensory integration of auditory (A) and visual (V) stimuli were investigated in humans using behavioral and electrophysiological measures. The aim was to find out whether cross-modal interactions between A and V stimuli depend on their spatial congruity, as has been found for multisensory neurons in animal studies (Stein & Meredith, 1993). Randomized sequences of unimodal (A or V) and simultaneous bimodal (AV) stimuli were presented to right- or left-field locations while subjects made speeded responses to infrequent targets of greater intensity that occurred in either or both modalities. Behavioral responses to the bimodal stimuli were faster and more accurate than to the unimodal stimuli for both same-location and different-location AV pairings. The neural basis of this cross-modal facilitation was studied by comparing event-related potentials (ERPs) to the bimodal AV stimuli with the summed ERPs to the unimodal A and V stimuli. These comparisons revealed neural interactions localized to the ventral occipito-temporal cortex (at 190 msec) and to the superior temporal cortical areas (at 260 msec) for both same- and different-location AV pairings. In contrast, ERP interactions that differed according to spatial congruity included a phase and amplitude modulation of visual-evoked activity localized to the ventral occipito-temporal cortex at 100-400 msec and an amplitude modulation of activity localized to the superior temporal region at 260-280 msec. These results demonstrate overlapping but distinctive patterns of multisensory integration for spatially congruent and incongruent AV stimuli.

Control mechanisms mediating shifts of attention in auditory and visual space: a spatio-temporal ERP analysis

The neural systems that mediate voluntary shifts of attention to visual and auditory stimuli were investigated by examining the patterns of human brain electricity elicited by attention-directing cues in auditory and visual tasks. Several lateralized event-related potential (ERP) components were observed when participants shifted attention in expectation of visual targets (experiment 1). One component was focused over frontal cortex and a second was focused primarily over the occipital-temporal cortex but also spread to parietal regions of the scalp. Previous work has indicated that the frontal component reflects supramodal processes involved in the executive control of attention and that the posterior component reflects either spatial attentional control processes in the posterior parietal lobe or modulation of processes in visual cortex. Here, the posterior component was observed when participants shifted attention in expectation of auditory targets (experiments 2-4), but the frontal component was found only in the visual task. The posterior component seemed to be generated in parietal and occipital areas even when there was no visual information about the to-be-attended locations. These results are consistent with the view that voluntary shifts of attention are mediated by supramodal processes in the parietal lobe and that the spatial coordinates of the to-be-attended location are based on visual representations of space.

Neural basis of auditory-induced shifts in visual time-order perception

Attended objects are perceived to occur before unattended objects even when the two objects are presented simultaneously. This finding has led to the widespread view that attention modulates the speed of neural transmission in the various perceptual pathways. We recorded event-related potentials during a time-order judgment task to determine whether a reflexive shift of attention to a sudden sound modulates the speed of sensory processing in the human visual system. Attentional cueing influenced the perceived order of lateralized visual events but not the timing of event-related potentials in visual cortex. Attentional cueing did, however, enhance the amplitude of neural activity in visual cortex, which shows that attention-induced shifts in visual time-order perception can arise from modulations of signal strength rather than processing speed in the early visual-cortical pathways.

Neural substrates of perceptual enhancement by cross-modal spatial attention

Orienting attention involuntarily to the location of a sudden sound improves perception of subsequent visual stimuli that appear nearby. The neural substrates of this cross-modal attention effect were investigated by recording event-related potentials to the visual stimuli using a dense electrode array and localizing their brain sources through inverse dipole modeling. A spatially nonpredictive auditory precue modulated visual-evoked neural activity first in the superior temporal cortex at 120-140 msec and then in the ventral occipital cortex of the fusiform gyrus 15-25 msec later. This spatio-temporal sequence of brain activity suggests that enhanced visual perception produced by the cross-modal orienting of spatial attention results from neural feedback from the multimodal superior temporal cortex to the visual cortex of the ventral processing stream.

An analysis of audio-visual crossmodal integration by means of event-related potential (ERP) recordings

Crossmodal integration was studied in humans by presenting random sequences of auditory (brief noise bursts), visual (flashes), and audiovisual (simultaneous noise bursts and flashes) stimuli from a central location at irregular intervals between 600 and 800 ms. The subjects' task was to press a button to infrequent and unpredictable (P=0.15) target stimuli that could be either a more intense noise burst, a brighter flash, or a combination of the two. In accordance with previous studies, behavioral data showed that bimodal target stimuli were responded to much faster and were identified more accurately than the unimodal target stimuli. The neural basis of this crossmodal interaction was investigated by subtracting the ERPs to the auditory (A) and the visual (V) stimuli alone from the ERP to the combined audiovisual (AV) stimuli (i.e. interaction=AV-(A+V)). Using this approach, we replicated previous reports of both early (at around 40 ms) and late (after 100 ms) ERP interaction effects. However, it appears that the very early interaction effects can be largely accounted for by an anticipatory ERP that precedes both the unimodal and bimodal stimuli. In calculating the ERP interaction this slow shift is subtracted twice, resulting in an apparent shift of the opposite polarity that may be confounded with actual crossmodal interactions.

Transient spatial attention modulates distinct components of the auditory ERP

We recorded ERPs to pairs of externally presented tones, T1 and T2, in the absence of attentional cues to determine whether attention is momentarily sustained at the location of a behaviourally relevant sound, and what effect this focusing of attention might have on the neural response to target stimuli. ERPs to T2 were more negative when the preceding T1 was presented on the same side of fixation than when T1 was presented on the opposite side of fixation. This negative difference consisted of an early, parietal phase and a later, frontocentral phase. These results confirm and extend previously reported effects of transient spatial attention on auditory ERPs, and they demonstrate that transient spatial attention has a distinct and robust effect on the early stages of stimulus processing in the auditory system.