Attentional capture by size singletons is determined by top-down search goals

The question whether attentional capture by salient visual stimuli is driven by bottom-up salience or is contingent on top-down task set is still under dispute. We show that the ability of size singletons to capture attention is determined by current search goals. Participants searched for small or large target singletons among medium-size distractors. Attentional capture by small or large size singleton cues that preceded target search displays was reflected by spatial cueing effects and N2pc components. These effects were observed only when these cues matched the current target-defining feature, but not for physically identical but mismatching cues. Results demonstrate that attentional capture by size singletons is not driven by bottom-up salience, but is controlled by feature-specific task settings.     

The absence of a visual stimulus can trigger task-set-independent attentional capture

We investigated whether the absence of one item in a regularly spaced visual array (gap cue) captures attention in a task-set-independent fashion. Participants searched for a large target among medium-size distractors (size task) or a red target among gray distractors (color task). Target arrays were preceded by uninformative cue arrays that contained a color singleton or a gap cue. The N2pc component was measured as an index of attentional capture. Color singleton cues captured attention only in the color task, but gap cues captured attention in both tasks. For cue arrays containing a color singleton and a gap cue on opposite sides, an N2pc was triggered by the color singleton in the color task. The absence of an item in a regular array triggered task-set-independent attentional capture when it was the only unique display feature, but not when a competing set-matching singleton was simultaneously present.     

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 revelations of trial history effects in a color oddball search task

In visual oddball search tasks, viewing a no‐target scene (i.e., no‐target selection trial) leads to the facilitation or delay of the search time for a target in a subsequent trial. Presumably, this selection failure leads to biasing attentional set and prioritizing stimulus features unseen in the no‐target scene. We observed attention‐related ERP components and tracked the course of attentional biasing as a function of trial history. Participants were instructed to identify color oddballs (i.e., targets) shown in varied trial sequences. The number of no‐target scenes preceding a target scene was increased from zero to two to reinforce attentional biasing, and colors presented in two successive no‐target scenes were repeated or changed to systematically bias attention to specific colors. For the no‐target scenes, the presentation of a second no‐target scene resulted in an early selection of, and sustained attention to, the changed colors (mirrored in the frontal selection positivity, the anterior N2, and the P3b). For the target scenes, the N2pc indicated an earlier allocation of attention to the targets with unseen or remotely seen colors. Inhibitory control of attention, shown in the anterior N2, was greatest when the target scene was followed by repeated no‐target scenes with repeated colors. Finally, search times and the P3b were influenced by both color previewing and its history. The current results demonstrate that attentional biasing can occur on a trial‐by‐trial basis and be influenced by both feature previewing and its history.     

Analgesia induced by self‐initiated electrotactile sensation is mediated by top‐down modulations

It is well known that sensory perception can be attenuated when sensory stimuli are controlled by self‐initiated actions. This phenomenon is explained by the consistency between forward models of anticipated action effects and actual sensory feedback. Specifically, the brain state related to the binding between motor processing and sensory perception would have inhibitory function by gating sensory information via top‐down control. Since the brain state could casually influence the perception of subsequent stimuli of different sensory modalities, we hypothesize that pain evoked by nociceptive stimuli following the self‐initiated tactile stimulation would be attenuated as compared to that following externally determined tactile stimulation. Here, we compared psychophysical and neurophysiological responses to identical nociceptive‐specific laser stimuli in two different conditions: self‐initiated tactile sensation condition (STS) and nonself‐initiated tactile sensation condition (N‐STS). We observed that pain intensity and unpleasantness, as well as laser‐evoked brain responses, were significantly reduced in the STS condition compared to the N‐STS condition. In addition, magnitudes of alpha and beta oscillations prior to laser onset were significantly larger in the STS condition than in the N‐STS condition. These results confirmed that pain perception and pain‐related brain responses were attenuated when the tactile stimulation was initiated by subjects’ voluntary actions, and exploited neural oscillations reflecting the binding between motor processing and sensory feedback. Thus, our study elaborated the understanding of underlying neural mechanisms related to top‐down modulations of the analgesic effect induced by self‐initiated tactile sensation, which provided theoretical basis to improve the analgesic effect in various clinical applications.     

Fast temporal event integration in the visual domain demonstrated by event‐related potentials

Four experiments are reported that investigated visual event integration by using a variant of the missing element paradigm. Good performance on this task depends on whether two brief successive stimulus displays are perceived as (or integrated into) one single event. We replicated the classic finding of greater accuracy with shorter duration of the first stimulus and ruled out an attention‐related account thereof. In a subsequent electrophysiological experiment we found that successful event integration increased the amplitude of the N1, N2, and late P3 components of the event‐related potential and decreased early P3 amplitude. No effect on the P1 was observed. The results provided evidence for an early onset of event integration in time and demonstrated the existence of electrophysiological markers of episodic integration. The implications of these results are related to studies on feature‐specific integration and early attentional processes.     

Age‐related changes in ERP correlates of visuospatial and motor processes

Although previous ERP studies have demonstrated slowing of visuospatial and motor processes with age, such studies frequently included only young and elderly participants, and lacked information about age‐related changes across the adult lifespan. The present research used a Simon task with two irrelevant dimensions (position and direction of an arrow) to study visuospatial (N2 posterior contralateral, N2pc) and motor (response‐locked lateralized readiness potential, LRP‐r) processes in young, middle‐aged, and elderly adults. The reaction time and motor execution stage (LRP‐r) increased gradually with age, while visuospatial processes (N2pc latency) were similarly delayed in the older groups. No age‐related increase in interference was observed, probably related to a delay in processing the symbolic meaning of the direction in older groups, which was consistent with age‐related differences in distributional analyses and N2pc amplitude modulations.     

The role of top‐down spatial attention in contingent attentional capture

It is well known that attentional capture by an irrelevant salient item is contingent on top‐down feature selection, but whether attentional capture may be modulated by top‐down spatial attention remains unclear. Here, we combined behavioral and ERP measurements to investigate the contribution of top‐down spatial attention to attentional capture under modified spatial cueing paradigms. Each target stimulus was preceded by a peripheral circular cue array containing a spatially uninformative color singleton cue. We varied target sets but kept the cue array unchanged among different experimental conditions. When participants’ task was to search for a colored letter in the target array that shared the same peripheral locations with the cue array, attentional capture by the peripheral color cue was reflected by both a behavioral spatial cueing effect and a cue‐elicited N2pc component. When target arrays were presented more centrally, both the behavioral and N2pc effects were attenuated but still significant. The attenuated cue‐elicited N2pc was found even when participants focused their attention on the fixed central location to identify a colored letter among an RSVP letter stream. By contrast, when participants were asked to identify an outlined or larger target, neither the behavioral spatial cueing effect nor the cue‐elicited N2pc was observed, regardless of whether the target and cue arrays shared same locations or not. These results add to the evidence that attentional capture by salient stimuli is contingent upon feature‐based task sets, and further indicate that top‐down spatial attention is important but may not be necessary for contingent attentional capture.     

Crossmodal links in spatial attention are mediated by supramodal control processes: evidence from event-related potentials

Crossmodal links in spatial attention were studied in an experiment where participants had to detect peripheral tactile or visual targets on the attended side, while ignoring all stimuli on the unattended side and in the currently irrelevant modality. Both relevant locations and relevant modalities were specified on a trial-by-trial basis by auditory precues. Spatial orienting in the cue-target interval was reflected in anterior negativities and occipital positivities contralateral to the cued side, either when vision or touch was cued as relevant. These effects resembled previously reported ERP modulations during shifts of visual attention, implicating supramodal mechanisms in the control of spatial attention and demonstrating their independence of cue modality. Early effects of spatial attention on somatosensory and visual ERPs were of equivalent size for currently relevant and irrelevant modalities. Results support the idea that crossmodal links in spatial attention are mediated by supramodal control mechanisms.     

On the role of conflict and control in social cognition: Event‐related brain potential investigations

Numerous social‐cognitive models posit that social behavior largely is driven by links between constructs in long‐term memory that automatically become activated when relevant stimuli are encountered. Various response biases have been understood in terms of the influence of such “implicit” processes on behavior. This article reviews event‐related potential (ERP) studies investigating the role played by cognitive control and conflict resolution processes in social‐cognitive phenomena typically deemed automatic. Neurocognitive responses associated with response activation and conflict often are sensitive to the same stimulus manipulations that produce differential behavioral responses on social‐cognitive tasks and that often are attributed to the role of automatic associations. Findings are discussed in the context of an overarching social cognitive neuroscience model in which physiological data are used to constrain social‐cognitive theories.     

An electrophysiological measure of visual short‐term memory capacity within and across hemifields

Recent electrophysiological research has identified a specific contralateral correlate of the contents of visual short‐term memory (VSTM). This posterior contralateral delay activity (CDA) persists during the retention period, and its amplitude is modulated by the number of items held at any one time. Here we show that, despite the contralateral nature of this activity, its amplitude is modulated by the number of objects from both hemifields. When objects from one side of the visual field are held in memory, CDA activity increased for arrays of one, two, and three objects, but stopped getting larger for arrays of four objects. However, when objects from both sides are memorized at the same time, CDA activity reached its asymptotic limit for arrays of two objects per side. These results suggest that, in spite of being contralaterally organized, VSTM is limited by the number of objects from both hemifields.     

Multisensory integration affects ERP components elicited by exogenous cues

Previous studies have shown that the amplitude of event related brain potentials (ERPs) elicited by a combined audiovisual stimulus is larger than the sum of a single auditory and visual stimulus. This enlargement is thought to reflect multisensory integration. Based on these data, it may be hypothesized that the speeding up of responses, due to exogenous orienting effects induced by bimodal cues, exceeds the sum of single unimodal cues. Behavioral data, however, typically revealed no increased orienting effect following bimodal as compared to unimodal cues, which could be due to a failure of multisensory integration of the cues. To examine this possibility, we computed ERPs elicited by both bimodal (audiovisual) and unimodal (either auditory or visual) cues, and determined their exogenous orienting effects on responses to a to-be-discriminated visual target. Interestingly, the posterior P1 component elicited by bimodal cues was larger than the sum of the P1 components elicited by a single auditory and visual cue (i.e., a superadditive effect), but no enhanced orienting effect was found on response speed. The latter result suggests that multisensory integration elicited by our bimodal cues plays no special role for spatial orienting, at least in the present setting.

Unintentional covert motor activations predict behavioral effects: Multilevel modeling of trial‐level electrophysiological motor activations

The present experiment measured an EEG indicator of motor cortex activation, the lateralized readiness potential (LRP), while participants performed a speeded category classification task. The LRP data showed that visually masked words triggered covert motor activations. These prime‐induced motor activations preceded motor activations by subsequent (to‐be‐classified) visible target words. Multilevel statistical analyses of trial‐level effects, applied here for the first time with electrophysiological data, revealed that accuracy and latency of classifying target words was affected by both (a) covert motor activations caused by visually masked primes and (b) spontaneous fluctuations in covert motor activations. Spontaneous covert motor fluctuations were unobserved with standard subject‐level (multi‐trial) analyses of grand‐averaged LRPs, highlighting the utility of multilevel modeling of trial‐level effects.     

Object‐substitution masking modulates spatial attention deployment and the encoding of information in visual short‐term memory: Insights from occipito‐parietal ERP components

If object‐substitution masking (OSM) arises from mask representations replacing target representations, OSM should impede the formation of representations in visual short‐term memory (VSTM). We utilized event‐related potentials to examine the effect of OSM on target processing. An N2pc was observed on trials with delayed‐offset masks, indicating that focused attention was directed to the target. The sustained posterior contralateral negativity (SPCN), an index of VSTM storage, was observed in delayed‐offset trials only on trials with correct responses. This supports the hypothesis that inaccurate performance on delayed‐offset trials arises from a failure to encode the target in VSTM. On co‐termination trials, accuracy was high and neither the N2pc nor SPCN was observed. This indicates that, in the absence of masking, the task was accomplished by maintaining a diffuse attentional state that enabled the joint encoding of the potential target items.     

Does focused endogenous attention prevent attentional capture in pop‐out visual search?

To investigate whether salient visual singletons capture attention when they appear outside the current endogenous attentional focus, we measured the N2pc component as a marker of attentional capture in a visual search task where target or nontarget singletons were presented at locations previously cued as task-relevant, or in the uncued irrelevant hemifield. In two experiments, targets were either defined by color or by a combination of color and shape. The N2pc was elicited both for attended singletons and for singletons on the uncued side, demonstrating that focused endogenous attention cannot prevent attentional capture by salient unattended visual events. However, N2pc amplitudes were larger for attended and unattended singletons that shared features with the current target, suggesting that top-down task sets modulate the capacity of visual singletons to capture attention both within and outside the current attentional focus.     

ERP correlates of dual mechanisms of control in the counting Stroop task

Event‐related brain potentials (ERPs) were used to examine the neural correlates of proactive and reactive cognitive control within the context of the Dual Mechanisms of Control theory. Individuals performed the counting Stroop task and the proportion of congruent and incongruent trials was varied across blocks. The Stroop effect was smaller in the mostly incongruent block than in the mostly congruent block. The ERP data revealed a double dissociation between the medial frontal negativity (MFN) and the medial posterior negativity (MPN), where the amplitude of the MFN was greater in the mostly incongruent block and the amplitude of the MPN was greater in the mostly congruent block. The ERP data also revealed slow wave activity that distinguished the mostly incongruent and mostly congruent blocks. These findings support the idea that different regions of the cingulate and anterior frontal cortex underpin proactive and reactive control.     

An ERP study of age‐related differences in the central cost of interlimb coordination

The study investigated event‐related EEG potentials during concurrent performance of interlimb coordination and visual oddball tasks by younger and older adults. Coordination task difficulty was equated between age groups by allowing participants to perform the task at self‐determined frequencies. The amplitude of the P3b component of the event‐related potentials (ERPs) elicited by visual task targets showed a different pattern across midline sites (Fz, Cz, Pz) for younger and older adults. While younger adults showed a parietal maximum, P3b amplitudes in older adults did not differ across midline site, with lower amplitudes at central and parietal sites than younger adults but higher amplitude at the frontal site. Younger adults also had significantly shorter P3b latency than older adults. The results suggest that older adults may rely more on cognitive control of their movements than younger adults.     

Visual working memory gives up attentional control early in learning: Ruling out interhemispheric cancellation

Current research suggests that we can watch visual working memory surrender the control of attention early in the process of learning to search for a specific object. This inference is based on the observation that the contralateral delay activity (CDA) rapidly decreases in amplitude across trials when subjects search for the same target object. Here, we tested the alternative explanation that the role of visual working memory does not actually decline across learning, but instead lateralized representations accumulate in both hemispheres across trials and wash out the lateralized CDA. We show that the decline in CDA amplitude occurred even when the target objects were consistently lateralized to a single visual hemifield. Our findings demonstrate that reductions in the amplitude of the CDA during learning are not simply due to the dilution of the CDA from interhemispheric cancellation.     

The category‐sensitive and orientation‐sensitive N170 adaptation in faces revealed by comparison with Chinese characters

By comparing faces with Chinese characters, the category‐sensitive and orientation‐sensitive N170 adaptation effects were examined when the stimuli were adapted by category (within vs. between) and orientation (same vs. different). The category‐sensitive N170 adaptation was present for both faces and characters, supporting the assertion that the perception of faces and characters recruits domain‐specific processing rather than general processing of visual expertise. In addition, the orientation‐sensitive N170 adaptation was present only for faces but not for characters, suggesting that only faces recruit orientation‐specific processing. More importantly, the orientation‐sensitive N170 adaptation was not only present for inverted faces but also for upright faces, indicating that there are distinct neuron populations respectively sensitive to upright and inverted faces.