Does spatial attention modulate the earliest component of the visual evoked potential?

Attention modulates early visual processing: An association between subjective contrast perception and early C1 ERP component

The question of whether spatial attention can modulate initial afferent activity in area V1, as measured by the earliest visual event-related potential (ERP) component "C1", is still the subject of debate. Because attention always enhances behavioral performance, previous research has focused on finding evidence of attention-related enhancements in visual neural responses. However, recent psychophysical studies revealed a complex picture of attention's influence on visual perception: attention amplifies the perceived contrast of low-contrast stimuli while dampening the perceived contrast of high-contrast stimuli. This evidence suggests that attention may not invariably augment visual neural responses but could instead exert inhibitory effects under certain circumstances. Whether this bi-directional modulation of attention also manifests in C1 and whether the modulation of C1 underpins the attentional influence on contrast perception remain unknown. To address these questions, we conducted two experiments (N = 67 in total) by employing a combination of behavioral and ERP methodologies. Our results did not unveil a uniform attentional enhancement or attenuation effect of C1 across all subjects. However, an intriguing correlation between the attentional effects of C1 and contrast appearance for high-contrast stimuli did emerge, revealing an association between attentional modulation of C1 and the attentional modulation of contrast appearance. This finding offers new insights into the relationship between attention, perceptual experience, and early visual neural processing, suggesting that the attentional effect on subjective visual perception could be mediated by the attentional modulation of the earliest visual cortical response.

Differential correlates of fear and anxiety in salience perception: A behavioral and ERP study with adolescents

Anxiety disorders are the most common psychopathologies among adolescents. Their diagnostic criteria include both fear and anxiety symptomatology, although according to the literature, we can find evidence for some distinction between these two emotions. The present study contribute to this distinction, exploring the effects of trait fear and trait anxiety on behavioral and neural correlates. Thirty-two participants (aged 11-16 years) performed two experimental tasks of salient target detection, including visual stimuli that were manipulated to become salient, while reaction times and EEG were recorded. Results of both tasks revealed differential effects of trait fear and trait anxiety assessed through the Fear Survey Schedule for Children-Revised and the Youth Anxiety Measure for DSM-5 on reaction times and ERP components amplitudes. Specifically, higher symptoms from Separation Anxiety Disorder increased early neural visual processing and decreased reaction times for more salient stimuli. Also, trait fear reduced later neural visual processing of salient stimuli. These findings may provide a significant contribution to guiding psychological interventions, especially with adolescents presenting higher levels of anxiety-related symptomatology.

Event Probabilities Have a Different Impact on Early and Late Electroencephalographic Measures Regarded as Metrics of Prediction

The oddball protocol has been used to study the neural and perceptual consequences of implicit predictions in the human brain. The protocol involves presenting a sequence of identical repeated events that are eventually broken by a novel "oddball" presentation. Oddball presentations have been linked to increased neural responding and to an exaggeration of perceived duration relative to repeated events. Because the number of repeated events in such protocols is circumscribed, as more repeats are encountered, the conditional probability of a further repeat decreases-whereas the conditional probability of an oddball increases. These facts have not been appreciated in many analyses of oddballs; repeats and oddballs have rather been treated as binary event categories. Here, we show that the human brain is sensitive to conditional event probabilities in an active, visual oddball paradigm. P300 responses (a relatively late component of visually evoked potentials measured with EEG) tended to be greater for less likely oddballs and repeats. By contrast, P1 responses (an earlier component) increased for repeats as a goal-relevant target presentation neared, but this effect occurred even when repeat probabilities were held constant, and oddball P1 responses were invariant. We also found that later, more likely oddballs seemed to last longer, and this effect was largely independent of the number of preceding repeats. These findings speak against a repetition suppression account of the temporal oddball effect. Overall, our data highlight an impact of event probability on later, rather than earlier, electroencephalographic measures previously related to predictive processes-and the importance of considering conditional probabilities in sequential presentation paradigms.

Catecholaminergic neuromodulation and selective attention jointly shape perceptual decision-making

Perceptual decisions about sensory input are influenced by fluctuations in ongoing neural activity, most prominently driven by attention and neuromodulator systems. It is currently unknown if neuromodulator activity and attention differentially modulate perceptual decision-making and/or whether neuromodulatory systems in fact control attentional processes. To investigate the effects of two distinct neuromodulatory systems and spatial attention on perceptual decisions, we pharmacologically elevated cholinergic (through donepezil) and catecholaminergic (through atomoxetine) levels in humans performing a visuo-spatial attention task, while we measured electroencephalography (EEG). Both attention and catecholaminergic enhancement improved decision-making at the behavioral and algorithmic level, as reflected in increased perceptual sensitivity and the modulation of the drift rate parameter derived from drift diffusion modeling. Univariate analyses of EEG data time-locked to the attentional cue, the target stimulus, and the motor response further revealed that attention and catecholaminergic enhancement both modulated pre-stimulus cortical excitability, cue- and stimulus-evoked sensory activity, as well as parietal evidence accumulation signals. Interestingly, we observed both similar, unique, and interactive effects of attention and catecholaminergic neuromodulation on these behavioral, algorithmic, and neural markers of the decision-making process. Thereby, this study reveals an intricate relationship between attentional and catecholaminergic systems and advances our understanding about how these systems jointly shape various stages of perceptual decision-making.

Single-subject electroencephalography measurement of interhemispheric transfer time for the in-vivo estimation of axonal morphology

Assessing axonal morphology in vivo opens new avenues for the combined study of brain structure and function. A novel approach has recently been introduced to estimate the morphology of axonal fibers from the combination of magnetic resonance imaging (MRI) data and electroencephalography (EEG) measures of the interhemispheric transfer time (IHTT). In the original study, the IHTT measures were computed from EEG data averaged across a group, leading to bias of the axonal morphology estimates. Here, we seek to estimate axonal morphology from individual measures of IHTT, obtained from EEG data acquired in a visual evoked potential experiment. Subject-specific IHTTs are computed in a data-driven framework with minimal a priori constraints, based on the maximal peak of neural responses to visual stimuli within periods of statistically significant evoked activity in the inverse solution space. The subject-specific IHTT estimates ranged from 8 to 29 ms except for one participant and the between-session variability was comparable to between-subject variability. The mean radius of the axonal radius distribution, computed from the IHTT estimates and the MRI data, ranged from 0 to 1.09 μm across subjects. The change in axonal g-ratio with axonal radius ranged from 0.62 to 0.81 μm-α . The single-subject measurement of the IHTT yields estimates of axonal morphology that are consistent with histological values. However, improvement of the repeatability of the IHTT estimates is required to improve the specificity of the single-subject axonal morphology estimates.

Crossmodal visual predictions elicit spatially specific early visual cortex activity but later than real visual stimuli

Previous studies have indicated that crossmodal visual predictions are instrumental in controlling early visual cortex activity. The exact time course and spatial precision of such crossmodal top-down influences on the visual cortex have been unknown. In the present study, participants were exposed to audiovisual combinations comprising one of two sounds and a Gabor patch either in the top left or in the bottom right visual field. Event-related potentials (ERPs) were recorded to these frequent crossmodal combinations (standards) as well as to trials in which the visual stimulus was omitted (omissions) or the visual and auditory stimuli were recombined (deviants). Standards and deviants elicited an ERP between 50 and 100 ms of opposite polarity known as the C1 effect commonly associated with retinotopic processing in early visual cortex. By contrast, a C1 effect was not observed in omission trials. Spatially specific omission and mismatch effects (deviants minus standards) started only later with a latency of 230 ms and 170 ms, respectively. These results suggest that crossmodal visual predictions control visual cortex activity in a spatially specific manner. However, visual predictions do not modulate visual cortex activity with the same timing as visual stimulation activates these areas but rather seem to involve distinct neural mechanisms. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Integrated effects of top-down attention and statistical learning during visual search: An EEG study

The present study aims to investigate how the competition between visual elements is solved by top-down and/or statistical learning (SL) attentional control (AC) mechanisms when active together. We hypothesized that the "winner" element that will undergo further processing is selected either by one AC mechanism that prevails over the other, or by the joint activity of both mechanisms. To test these hypotheses, we conducted a visual search experiment that combined an endogenous cueing protocol (valid vs. neutral cue) and an imbalance of target frequency distribution across locations (high- vs. low-frequency location). The unique and combined effects of top-down control and SL mechanisms were measured on behaviour and amplitudes of three evoked-response potential (ERP) components (i.e., N2pc, P1, CNV) related to attentional processing. Our behavioural results showed better performance for validly cued targets and for targets in the high-frequency location. The two factors were found to interact, so that SL effects emerged only in the absence of top-down guidance. Whereas the CNV and P1 only displayed a main effect of cueing, for the N2pc we observed an interaction between cueing and SL, revealing a cueing effect for targets in the low-frequency condition, but not in the high-frequency condition. Thus, our data support the view that top-down control and SL work in a conjoint, integrated manner during target selection. In particular, SL mechanisms are reduced or even absent when a fully reliable top-down guidance of attention is at play.

Bridging the gap between believing and memory functions

Believing has recently been recognized as a fundamental brain function linking a person’s experience with his or her attitude, actions and predictions. In general, believing results from the integration of ambient information with emotions and can be reinforced or modulated in a probabilistic fashion by new experiences. Although these processes occur in the subliminal realm, humans can become aware of what they believe and express it verbally. We explain how believing is interwoven with memory functions in a multifaceted fashion. Linking the typically rapid and adequate reactions of a subject to what he/she believes is enabled by working memory. Perceptions are stored in episodic memory as beneficial or aversive events, while the corresponding verbal descriptions of what somebody believes are stored in semantic memory. After recall from memory of what someone believes, personally relevant information can be communicated to other people. Thus, memory is essential for maintaining what people believe.

Cognitive penetrability of scene representations based on horizontal image disparities

The structure of natural scenes is signaled by many visual cues. Principal amongst them are the binocular disparities created by the laterally separated viewpoints of the two eyes. Disparity cues are believed to be processed hierarchically, first in terms of local measurements of absolute disparity and second in terms of more global measurements of relative disparity that allow extraction of the depth structure of a scene. Psychophysical and oculomotor studies have suggested that relative disparities are particularly relevant to perception, whilst absolute disparities are not. Here, we compare neural responses to stimuli that isolate the absolute disparity cue with stimuli that contain additional relative disparity cues, using the high temporal resolution of EEG to determine the temporal order of absolute and relative disparity processing. By varying the observers' task, we assess the extent to which each cue is cognitively penetrable. We find that absolute disparity is extracted before relative disparity, and that task effects arise only at or after the extraction of relative disparity. Our results indicate a hierarchy of disparity processing stages leading to the formation of a proto-object representation upon which higher cognitive processes can act.

Dynamics of retinotopic spatial attention revealed by multifocal MEG

Visual focal attention is both fast and spatially localized, making it challenging to investigate using human neuroimaging paradigms. Here, we used a new multivariate multifocal mapping method with magnetoencephalography (MEG) to study how focal attention in visual space changes stimulus-evoked responses across the visual field. The observer's task was to detect a color change in the target location, or at the central fixation. Simultaneously, 24 regions in visual space were stimulated in parallel using an orthogonal, multifocal mapping stimulus sequence. First, we used univariate analysis to estimate stimulus-evoked responses in each channel. Then we applied multivariate pattern analysis to look for attentional effects on the responses. We found that attention to a target location causes two spatially and temporally separate effects. Initially, attentional modulation is brief, observed at around 60-130 ms post stimulus, and modulates responses not only at the target location but also in adjacent regions. A later modulation was observed from around 200 ms, which was specific to the location of the attentional target. The results support the idea that focal attention employs several processing stages and suggest that early attentional modulation is less spatially specific than late.

Effects of selective attention on the C1 ERP component: A systematic review and meta-analysis

The C1 event-related potential (ERP) captures the earliest stage of feedforward processing in the primary visual cortex (V1). An ongoing debate is whether top-down selective attention can modulate the C1. One side of the debate pointed out that null findings appear to outnumber positive findings; thus, selective attention does not seem to influence the C1. However, this suggestion is not based on a valid approach to summarizing evidence across studies. Therefore, we conducted a systematic review and meta-analysis investigating the effects of selective attention on the C1, involving 47 experiments and 794 subjects in total. Despite heterogeneity across studies, results suggested that attention has a moderate effect on the C1 (Cohen's d z $$ {d}_z $$  = 0.33, p < .0001); that is, C1 amplitude is larger for visual stimuli that are attended than unattended. These results suggest that C1 is affected by top-down selective attention.

Effects of top-down influence suppression on behavioral and V1 neuronal contrast sensitivity functions in cats

To explore the relative contributions of higher-order and primary visual cortex (V1) to visual perception, we compared cats' behavioral and V1 neuronal contrast sensitivity functions (CSF) and threshold versus external noise contrast (TvC) functions before and after top-down influence of area 7 (A7) was modulated with transcranial direct current stimulation (tDCS). We found that suppressing top-down influence of A7 with cathode-tDCS, but not sham-tDCS, reduced behavioral and neuronal contrast sensitivity in the same range of spatial frequencies and increased behavioral and neuronal contrast thresholds in the same range of external noise levels. The neuronal CSF and TvC functions were highly correlated with their behavioral counterparts both before and after the top-down suppression. Analysis of TvC functions using the Perceptual Template Model (PTM) indicated that top-down influence of A7 increased both behavioral and V1 neuronal contrast sensitivity by reducing internal additive noise and the impact of external noise.

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Top-down suppression lowers both behavioral and V1 neuronal CSF functions

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Top-down suppression raises both behavioral and V1 neuronal TvC functions

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The neuronal CSFs and TvCs are highly correlated with their behavioral counterparts

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Top-down influence lowers internal additive noise and impact of external noise in V1

Top-Down Modulation of Early Visual Processing in V1: Dissociable Neurophysiological Effects of Spatial Attention, Attentional Load and Task-Relevance

Until today, there is an ongoing discussion if attention processes interact with the information processing stream already at the level of the C1, the earliest visual electrophysiological response of the cortex. We used two highly powered experiments (each N = 52) and examined the effects of task relevance, spatial attention, and attentional load on individual C1 amplitudes for the upper or lower visual hemifield. Bayesian models revealed evidence for the absence of load effects but substantial modulations by task-relevance and spatial attention. When the C1-eliciting stimulus was a task-irrelevant, interfering distracter, we observed increased C1 amplitudes for spatially unattended stimuli. For spatially attended stimuli, different effects of task-relevance for the two experiments were found. Follow-up exploratory single-trial analyses revealed that subtle but systematic deviations from the eye-gaze position at stimulus onset between conditions substantially influenced the effects of attention and task relevance on C1 amplitudes, especially for the upper visual field. For the subsequent P1 component, attentional modulations were clearly expressed and remained unaffected by these deviations. Collectively, these results suggest that spatial attention, unlike load or task relevance, can exert dissociable top-down modulatory effects at the C1 and P1 levels.

Suppression of top-down influence decreases neuronal excitability and contrast sensitivity in the V1 cortex of cat

How top-down influence affects neuronal activity and information encoding in the primary visual cortex (V1) remains elusive. This study examined changes of neuronal excitability and contrast sensitivity in cat V1 cortex after top-down influence of area 7 (A7) was modulated by transcranial direct current stimulation (tDCS). The neuronal excitability in V1 cortex was evaluated by visually evoked field potentials (VEPs), and contrast sensitivity (CS) was assessed by the inverse of threshold contrast of neurons in response to visual stimuli at different performance accuracy. We found that the amplitude of VEPs in V1 cortex lowered after top-down influence suppression with cathode-tDCS in A7, whereas VEPs in V1 did not change after sham-tDCS in A7 and nonvisual cortical area 5 (A5) or cathode-tDCS in A5 and lesioned A7. Moreover, the mean CS of V1 neurons decreased after cathode-tDCS but not sham-tDCS in A7, which could recover after tDCS effect vanished. Comparisons of neuronal contrast-response functions showed that cathode-tDCS increased the stimulus contrast required to generate the half-maximum response, with a weakly-correlated reduction in maximum response but not baseline response. Therefore, top-down influence of A7 enhanced neuronal excitability in V1 cortex and improved neuronal contrast sensitivity by both contrast gain and response gain.

Modulation of the Earliest Component of the Human VEP by Spatial Attention: An Investigation of Task Demands

Spatial attention modulations of initial afferent activity in area V1, indexed by the first component “C1” of the human visual evoked potential, are rarely found. It has thus been suggested that early modulation is induced only by special task conditions, but what these conditions are remains unknown. Recent failed replications—findings of no C1 modulation using a certain task that had previously produced robust modulations—present a strong basis for examining this question. We ran 3 experiments, the first to more exactly replicate the stimulus and behavioral conditions of the original task, and the second and third to manipulate 2 key factors that differed in the failed replication studies: the provision of informative performance feedback, and the degree to which the probed stimulus features matched those facilitating target perception. Although there was an overall significant C1 modulation of 11%, individually, only experiments 1 and 2 showed reliable effects, underlining that the modulations do occur but not consistently. Better feedback induced greater P1, but not C1, modulations. Target-probe feature matching had an inconsistent influence on modulation patterns, with behavioral performance differences and signal-overlap analyses suggesting interference from extrastriate modulations as a potential cause.

Characterization of Feedback Neurons in the High-Level Visual Cortical Areas That Project Directly to the Primary Visual Cortex in the Cat

Previous studies indicate that top-down influence plays a critical role in visual information processing and perceptual detection. However, the substrate that carries top-down influence remains poorly understood. Using a combined technique of retrograde neuronal tracing and immunofluorescent double labeling, we characterized the distribution and cell type of feedback neurons in cat's high-level visual cortical areas that send direct connections to the primary visual cortex (V1: area 17). Our results showed: (1) the high-level visual cortex of area 21a at the ventral stream and PMLS area at the dorsal stream have a similar proportion of feedback neurons back projecting to the V1 area, (2) the distribution of feedback neurons in the higher-order visual area 21a and PMLS was significantly denser than in the intermediate visual cortex of area 19 and 18, (3) feedback neurons in all observed high-level visual cortex were found in layer II-III, IV, V, and VI, with a higher proportion in layer II-III, V, and VI than in layer IV, and (4) most feedback neurons were CaMKII-positive excitatory neurons, and few of them were identified as inhibitory GABAergic neurons. These results may argue against the segregation of ventral and dorsal streams during visual information processing, and support "reverse hierarchy theory" or interactive model proposing that recurrent connections between V1 and higher-order visual areas constitute the functional circuits that mediate visual perception. Also, the corticocortical feedback neurons from high-level visual cortical areas to the V1 area are mostly excitatory in nature.

A Spelling Paradigm With an Added Red Dot Improved the P300 Speller System Performance

The traditional P300 speller system uses the flashing row or column spelling paradigm. However, the classification accuracy and information transfer rate of the P300 speller are not adequate for real-world application. To improve the performance of the P300 speller, we devised a new spelling paradigm in which the flashing row or column of a virtual character matrix is covered by a translucent green circle with a red dot in either the upper or lower half (GC-RD spelling paradigm). We compared the event-related potential (ERP) waveforms with a control paradigm (GC spelling paradigm), in which the flashing row or column of a virtual character matrix was covered by a translucent green circle only. Our experimental results showed that the amplitude of P3a at the parietal area and P3b at the frontal–central–parietal areas evoked by the GC-RD paradigm were significantly greater than those induced by the GC paradigm. Higher classification accuracy and information transmission rates were also obtained in the GC-RD system. Our results indicated that the added red dots increased attention and visuospatial information, resulting in an amplitude increase in both P3a and P3b, thereby improving the performance of the P300 speller system.

Spatial attention modulates earliest visual processing: An electrical neuroimaging study

Several studies showed that shifting of visuospatial attention modulates sensory processing at multiple levels of the visual pathways and beyond, including the occipital striate cortices level. However, inconsistent findings have been reported thus leaving these issues still disputed. 21 participants took part to the present study (the EEG signals of 4 of them were discarded due to artifacts). We used ERPs and their neural sources to investigate whether shifting spatial attention in space across the horizontal meridian of the visual field affected striate cortices activation at the earliest latency. Time-series of scalp topographical maps indicated that, unlike ERPs to attentional-neutral central cues, ERPs to attention-directing local cues showed earliest polarity inversions as a function of stimulated field and processing latency range considered, at occipital-parietal electrodes. In between 60-75 ms, attentional shifting cues elicited a positivity for both visual fields, whereas at a later latency (75–90 ms) they elicited a positivity and a negativity for the upper and lower visual hemifields, respectively. Computed neural sources included striate, besides extrastriate, cortices for both visual hemifields and latency ranges. Conjointly, behavioral responses to targets were faster when they were preceded by local than by neutral cues, and when presented in the upper than the lower hemifield. Our findings support the hypothesis that attention shifts may affect early sensory processing in visual cortices.

No Evidence that Predictions and Attention Modulate the First Feedforward Sweep of Cortical Information Processing

Predictive coding models propose that predictions (stimulus likelihood) reduce sensory signals as early as primary visual cortex (V1), and that attention (stimulus relevance) can modulate these effects. Indeed, both prediction and attention have been shown to modulate V1 activity, albeit with fMRI, which has low temporal resolution. This leaves it unclear whether these effects reflect a modulation of the first feedforward sweep of visual information processing and/or later, feedback-related activity. In two experiments, we used electroencephalography and orthogonally manipulated spatial predictions and attention to address this issue. Although clear top-down biases were found, as reflected in pre-stimulus alpha-band activity, we found no evidence for top-down effects on the earliest visual cortical processing stage (<80 ms post-stimulus), as indexed by the amplitude of the C1 event-related potential component and multivariate pattern analyses. These findings indicate that initial visual afferent activity may be impenetrable to top-down influences by spatial prediction and attention.

Low frequency transcranial magnetic stimulation of right posterior parietal cortex reduces reaction time to perithreshold low spatial frequency visual stimuli

Research in humans and animal models suggests that visual responses in early visual cortical areas may be modulated by top-down influences from distant cortical areas, particularly in the frontal and parietal regions. The right posterior parietal cortex is part of a broad cortical network involved in aspects of visual search and attention, but its role in modulating activity in early visual cortical areas is less well understood. This study evaluated the influence of right posterior parietal cortex (PPC) on a direct measure of visual processing in humans. Contrast sensitivity (CS) and detection response times were recorded using a visual detection paradigm to two types of centrally-presented stimuli. Participants were tested on the detection task before, after, and 1 hour after low-frequency repetitive transcranial magnetic stimulation (rTMS) to the right PPC or to the scalp vertex. Low-frequency rTMS to the right PPC did not significantly change measures of contrast sensitivity, but increased the speed at which participants responded to visual stimuli of low spatial frequency. Response times returned to baseline 1-hour after rTMS. These data indicate that low frequency rTMS to the right PPC speeds up aspects of early visual processing, likely due to a disinhibition of the homotopic left posterior parietal cortex.

Short- and long-term forms of neural adaptation: An ERP investigation of dynamic motion aftereffects

Adaptation is essential to interact with a dynamic and changing environment, and can be observed on different timescales. Previous studies on a motion paradigm called dynamic motion aftereffect (dMAE) showed that neural adaptation can establish even in very short timescales. However, the neural mechanisms underlying such rapid form of neural plasticity is still debated. In the present study, short- and long-term forms of neural plasticity were investigated using dynamic motion aftereffect combined with EEG (Electroencephalogram). Participants were adapted to directional drifting gratings for either short (640 msec) or long (6.4 sec) durations. Both adaptation durations led to motion aftereffects on the perceived direction of a dynamic and directionally ambiguous test pattern, but the long adaptation produced stronger dMAE. In line with behavioral results, we found robust changes in the event-related potentials elicited by the dynamic test pattern within 64-112 msec time range. These changes were mainly clustered over occipital and parieto-occipital scalp sites. Within this time range, the aftereffects induced by long adaptation were stronger than those by short adaptation. Moreover, the aftereffects by each adaptation duration were in the opposite direction. Overall, these EEG findings suggest that dMAEs reflect changes in cortical areas mediating low- and mid-level visual motion processing. They further provide evidence that short- and long-term forms of motion adaptation lead to distinct changes in neural activity, and hence support the view that adaptation is an active time-dependent process which involves different neural mechanisms.

Modulation of Event-related Potentials of Visual Discrimination by Meditation Training and Sustained Attention

The ability to discriminate among goal-relevant stimuli tends to diminish when detections must be made continuously over time. Previously, we reported that intensive training in shamatha (focused-attention) meditation can improve perceptual discrimination of difficult-to-detect visual stimuli [MacLean, K. A., Ferrer, E., Aichele, S. R., Bridwell, D. A., Zanesco, A. P., Jacobs, T. L., et al. Intensive meditation training improves perceptual discrimination and sustained attention. Psychological Science, 21, 829-839, 2010]. Here we extend these findings to examine how discrimination difficulty and meditation training interact to modulate event-related potentials of attention and perceptual processing during vigilance. Training and wait-list participants completed a continuous performance task at the beginning, middle, and end of two 3-month meditation interventions. In the first intervention (Retreat 1), the continuous performance task target was adjusted across assessments to match training-related changes in participants' perceptual capacity. In the second intervention (Retreat 2), the target was held constant across training, irrespective of changes in discrimination capacity. No training effects were observed in Retreat 1, whereas Retreat 2 was associated with changes in the onset of early sensory signals and an attenuation of within-task decrements at early latencies. In addition, changes at later stimulus processing stages were directly correlated with improvements in perceptual threshold across the second intervention. Overall, these findings demonstrate that improvements in perceptual discrimination can modulate electrophysiological markers of perceptual processing and attentional control during sustained attention, but likely only under conditions where an individual's discrimination capacity is allowed to exceed the demand imposed by the difficulty of a visual target. These results contribute to basic understanding of the dependence of perceptual processing and attentional control to contextual demands and their susceptibility to directed mental training.

Neural Correlates of Enhanced Visual Attentional Control in Action Video Game Players: An Event-Related Potential Study

Action video game players (AVGPs) outperform non–action video game players (NAVGPs) on a range of perceptual and attentional tasks. Although several studies have reported neuroplastic changes within the frontoparietal networks of attention in AVGPs, little is known about possible changes in attentional modulation in low-level visual areas. To assess the contribution of these different levels of neural processing to the perceptual and attentional enhancements noted in AVGPs, visual event-related potentials (ERPs) were recorded from 14 AVGPs and 14 NAVGPs during a target discrimination task that required participants to attend to rapid sequences of Gabor patches under either focused or divided attention conditions. AVGPs responded faster to target Gabors in the focused attention condition compared with the NAVGPs. Correspondingly, ERPs to standard Gabors revealed a more pronounced negativity in the time range of the parietally generated anterior N1 component in AVGPs compared with NAVGPs during focused attention. In addition, the P2 component of the visual ERP was more pronounced in AVGPs than in NAVGPs over the hemisphere contralateral to the stimulus position in response to standard Gabors. Contrary to predictions, however, attention-modulated occipital components generated in the low-level extrastriate visual pathways, including the P1 and posterior N1, showed no significant group differences. Thus, the main neural signature of enhanced perceptual and attentional control functions in AVGPs appears linked to an attention-dependent parietal process, indexed by the anterior N1 component, and possibly to more efficient higher-order perceptual processing, indexed by the P2 component.

Auditory spatial attention modulates the unmasking effect of perceptual separation in a "cocktail party" environment

The perceptual separation between a signal speech and a competing speech (masker), induced by the precedence effect, plays an important role in releasing the signal speech from the masker, especially in a reverberant environment. The perceptual-separation-induced unmasking effect has been suggested to involve multiple cognitive processes, such as selective attention. However, whether listeners' spatial attention modulate the perceptual-separation-induced unmasking effect is not clear. The present study investigated how perceptual separation and auditory spatial attention interact with each other to facilitate speech perception under a simulated noisy and reverberant environment by analyzing the cortical auditory evoked potentials to the signal speech. The results showed that the N1 wave was significantly enhanced by perceptual separation between the signal and masker regardless of whether the participants' spatial attention was directed to the signal or not. However, the P2 wave was significantly enhanced by perceptual separation only when the participants attended to the signal speech. The results indicate that the perceptual-separation-induced facilitation of P2 needs more attentional resource than that of N1. The results also showed that the signal speech caused an enhanced N1 in the contralateral hemisphere regardless of whether participants' attention was directed to the signal or not. In contrast, the signal speech caused an enhanced P2 in the contralateral hemisphere only when the participant attended to the signal. The results indicate that the hemispheric distribution of N1 is mainly affected by the perceptual features of the acoustic stimuli, while that of P2 is affected by the listeners' attentional status.

Detailed spatiotemporal brain mapping of chromatic vision combining high-resolution VEP with fMRI and retinotopy

Neuroimaging studies have identified so far, several color-sensitive visual areas in the human brain, and the temporal dynamics of these activities have been separately investigated using the visual-evoked potentials (VEPs). In the present study, we combined electrophysiological and neuroimaging methods to determine a detailed spatiotemporal profile of chromatic VEP and to localize its neural generators. The accuracy of the present co-registration study was obtained by combining standard fMRI data with retinotopic and motion mapping data at the individual level. We found a sequence of occipito activities more complex than that typically reported for chromatic VEPs, including feed-forward and reentrant feedback. Results showed that chromatic human perception arises by the combined activity of at the least five parieto-occipital areas including V1, LOC, V8/VO, and the motion-sensitive dorsal region MT+. However, the contribution of V1 and V8/VO seems dominant because the re-entrant activity in these areas was present more than once (twice in V8/VO and thrice in V1). This feedforward and feedback chromatic processing appears delayed compared with the luminance processing. Associating VEPs and neuroimaging measures, we showed for the first time a complex spatiotemporal pattern of activity, confirming that chromatic stimuli produce intricate interactions of many different brain dorsal and ventral areas.

The spatiotemporal characteristics of the C1 component and its modulation by attention

Slotnick (this issue) provided a selective review of studies on the attentional modulation of the C1 component of the visual evoked potential, and offers a number of guidelines to maximize the likelihood of observing such modulation in terms of electrode choice, stimulus placement, and types of attentional cue and target stimulus. However, the broader literature pertaining to attentional modulation of the C1 does not support many of these guidelines, and the question of why exactly C1 modulations are so rare remains very much open. Here, we provide clarifications that are critical to an accurate appraisal of the current state of this literature.