N250r and N400 ERP correlates of immediate famous face repetition are independent of perceptual load

The neural dynamics of familiar face recognition

Humans are highly efficient at recognising familiar faces. However, previous EEG/ERP research has given a partial and fragmented account of the neural basis of this remarkable ability. We argue that this is related to insufficient consideration of fundamental characteristics of familiar face recognition. These include image-independence (recognition across different pictures), levels of familiarity (familiar faces vary hugely in duration and intensity of our exposure to them), automaticity (we cannot voluntarily withhold from recognising a familiar face), and domain-selectivity (the degree to which face familiarity effects are selective). We review recent EEG/ERP work, combining uni- and multivariate methods, that has systematically targeted these shortcomings. We present a theoretical account of familiar face recognition, dividing it into early visual, domain-sensitive and domain-general phases, and integrating image-independence and levels of familiarity. Our account incorporates classic and more recent concepts, such as multi-dimensional face representation and course-to-fine processing. While several questions remain to be addressed, this new account represents a major step forward in our understanding of the neurophysiological basis of familiar face recognition.

No electrophysiological evidence for semantic processing during inattentional blindness

A long-standing question concerns whether sensory input can reach semantic stages of processing in the absence of attention and awareness. Here, we examine whether the N400, an event related potential associated with semantic processing, can occur under conditions of inattentional blindness. By employing a novel three-phase inattentional blindness paradigm designed to maximise the opportunity for detecting an N400, we found no evidence for it when participants were inattentionally blind to the eliciting stimuli (related and unrelated word pairs). In contrast, participants noticed the same task-irrelevant word pairs when minimal attention was allocated to them, and a small N400 became evident. When the same stimuli were fully attended and relevant to the task, a robust N400 was observed. In addition to univariate ERP measures, multivariate decoding analyses were unable to classify related from unrelated word pairs when observers were inattentionally blind to the words, with decoding reaching above-chance levels only when the words were (at least minimally) attended. By comparison, decoding reached above-chance levels when contrasting word pairs with non-word stimuli, even when participants were inattentionally blind to these stimuli. Our results also replicated several previous studies by finding a "visual awareness negativity" (VAN) that distinguished task-irrelevant stimuli that participants noticed compared with those that were not perceived, and a P3b (or "late positivity") that was evident only when the stimuli were task relevant. Together, our findings suggest that semantic processing might require at least a minimal amount of attention.

How to do Better N400 Studies: Reproducibility, Consistency and Adherence to Research Standards in the Existing Literature

Given the complexity of ERP recording and processing pipeline, the resulting variability of methodological options, and the potential for these decisions to influence study outcomes, it is important to understand how ERP studies are conducted in practice and to what extent researchers are transparent about their data collection and analysis procedures. The review gives an overview of methodology reporting in a sample of 132 ERP papers, published between January 1980 - June 2018 in journals included in two large databases: Web of Science and PubMed. Because ERP methodology partly depends on the study design, we focused on a well-established component (the N400) in the most commonly assessed population (healthy neurotypical adults), in one of its most common modalities (visual images). The review provides insights into 73 properties of study design, data pre-processing, measurement, statistics, visualization of results, and references to supplemental information across studies within the same subfield. For each of the examined methodological decisions, the degree of consistency, clarity of reporting and deviations from the guidelines for best practice were examined. Overall, the results show that each study had a unique approach to ERP data recording, processing and analysis, and that at least some details were missing from all papers. In the review, we highlight the most common reporting omissions and deviations from established recommendations, as well as areas in which there was the least consistency. Additionally, we provide guidance for a priori selection of the N400 measurement window and electrode locations based on the results of previous studies.

The Time Sequence of Face Spatial Frequency Differs During Working Memory Encoding and Retrieval Stages

Previous studies have found that P1 and P2 components were more sensitive to configural and featural face processing, respectively, when attentional resources were sufficient, suggesting that face processing follows a coarse-to-fine sequence. However, the role of working memory (WM) load in the time course of configural and featural face processing is poorly understood, especially whether it differs during encoding and retrieval stages. This study employed a delayed recognition task with varying WM load and face spatial frequency (SF). Our behavioral and ERP results showed that WM load modulated face SF processing. Specifically, for the encoding stage, P1 and P2 were more sensitive to broadband SF (BSF) faces, while N170 was more sensitive to low SF (LSF) and BSF faces. For the retrieval stage, P1 on the right hemisphere was more sensitive to BSF faces relative to HSF faces, N170 was more sensitive to LSF faces than HSF faces, especially under the load 1 condition, while P2 was more sensitive to high SF (HSF) faces than HSF faces, especially under load 3 condition. These results indicate that faces are perceived less finely during the encoding stage, whereas face perception follows a coarse-to-fine sequence during the retrieval stage, which is influenced by WM load. The coarse and fine information were processed especially under the low and high load conditions, respectively.

Detecting a viewer's familiarity with a face: Evidence from event-related brain potentials and classifier analyses

Human observers recognize the faces of people they know efficiently and without apparent effort. Consequently, recognizing a familiar face is often assumed to be an automatic process beyond voluntary control. However, there are circumstances in which a person might seek to hide their recognition of a particular face. The present study therefore used event-related potentials (ERPs) and a classifier based on logistic regression to determine if it is possible to detect whether a viewer is familiar with a particular face, regardless of whether the participant is willing to acknowledge it or not. In three experiments, participants were presented with highly variable "ambient" images of personally familiar and unfamiliar faces, while performing an incidental butterfly detection task (Experiment 1), an explicit familiarity judgment task (Experiment 2), and a concealed familiarity task in which they were asked to deny familiarity with one truly known facial identity while acknowledging familiarity with a second known identity (Experiment 3). In all three experiments, we observed substantially more negative ERP amplitudes at occipito-temporal electrodes for familiar relative to unfamiliar faces starting approximately 200 ms after stimulus onset. Both the earlier N250 familiarity effect, reflecting visual recognition of a known face, and the later sustained familiarity effect, reflecting the integration of visual with additional identity-specific information, were similar across experiments and thus independent of task demands. These results were further supported by the classifier analysis. We conclude that ERP correlates of familiar face recognition are largely independent of voluntary control and discuss potential applications in forensic settings.

Faces are not always special for attention: Effects of response-relevance and identity

Research over the past 25 years indicates that stimulus processing is diminished when attention is engaged in a perceptually demanding task of high 'perceptual load'. These results have generalized across a variety of stimulus categories, but a controversy evolved over the question of whether perception of distractor faces (or other categories of perceptual expertise) can proceed irrespective of the level of perceptual load in the attended task. Here we identify task-relevance, and in particular identity-relevance, as a potentially important factor in explaining prior inconsistencies. In four experiments, we tested whether perceptual load in an attended letter or word task modulates the processing of famous face distractors, while varying their task-relevance. Distractor interference effects on task RTs was reduced by perceptual load not only when the faces were entirely task-irrelevant, but also when the face gender was task relevant, within a name gender classification response-competition task, using famous female or male distractor faces. However, when the identity associated with the famous faces was primed by the task using their names, as in prior demonstrations that face distractors are immune to the effects of perceptual load, we were able to replicate these prior findings. Our findings demonstrate a role for identity-priming by the relevant task in determining attentional capture by faces under high perceptual load. Our results also highlight the importance of considering even relatively subtle forms of task-relevance in selective attention research.

Reflections and New Perspectives on Face Cognition as a Specific Socio-Cognitive Ability

The study of socio-cognitive abilities emerged from intelligence research, and their specificity remains controversial until today. In recent years, the psychometric structure of face cognition (FC)-a basic facet of socio-cognitive abilities-was extensively studied. In this review, we summarize and discuss the divergent psychometric structures of FC in easy and difficult tasks. While accuracy in difficult tasks was consistently shown to be face-specific, the evidence for easy tasks was inconsistent. The structure of response speed in easy tasks was mostly-but not always-unitary across object categories, including faces. Here, we compare studies to identify characteristics leading to face specificity in easy tasks. The following pattern emerges: in easy tasks, face specificity is found when modeling speed in a single task; however, when modeling speed across multiple, different easy tasks, only a unitary factor structure is reported. In difficult tasks, however, face specificity occurs in both single task approaches and task batteries. This suggests different cognitive mechanisms behind face specificity in easy and difficult tasks. In easy tasks, face specificity relies on isolated cognitive sub-processes such as face identity recognition. In difficult tasks, face-specific and task-independent cognitive processes are employed. We propose a descriptive model and argue for FC to be integrated into common taxonomies of intelligence.

The Effect of Visual Perceptual Load on Auditory Awareness of Social vs. Non-social Stimuli in Individuals with Autism

This study examined the effect of increasing visual perceptual load on auditory awareness for social and non-social stimuli in adolescents with autism spectrum disorder (ASD, n = 63) and typically developing (TD, n = 62) adolescents. Using an inattentional deafness paradigm, a socially meaningful ('Hi') or a non-social (neutral tone) critical stimulus (CS) was unexpectedly presented under high and low load. For the social CS both groups continued to show high awareness rates as load increased. Awareness rates for the non-social stimulus were reduced when load increased for the TD, but not the ASD group. The findings indicate enhanced capacity for non-social stimuli in ASD compared to TD, and a special attentional status for social stimuli in the TD group.

Face Recognition Deficits in a Patient With Alzheimer's Disease: Amnesia or Agnosia? The Importance of Electrophysiological Markers for Differential Diagnosis

Face recognition deficits are frequently reported in Alzheimer's disease (AD) and often attributed to memory impairment. However, it has been hypothesized that failure in identifying familiar people could also be due to deficits in higher-level perceptual processes, since there is evidence showing a reduced inversion effect for faces but not for cars in AD. To address the involvement of these higher processes, we investigated event-related potential (ERP) neural correlates of faces in a patient with AD showing a face recognition deficit. Eight healthy participants were tested as a control group. Participants performed different tasks following the stimulus presentation. In experiment 1, they should indicate whether the stimulus was either a face or a house or a scrambled image. In experiments 2 and 3, they should discriminate between upright and inverted faces (in experiment 2, stimuli were faces with neutral or fearful expressions, while in experiment 3, stimuli were famous or unfamiliar faces). Electrophysiological results reveal that the typical face-specific modulation of the N170 component, which is thought to reflect the structural encoding of faces, was not present in patient MCG, despite being affected by the emotional content of the face implicitly processed by MCG. Conversely, the N400 component, which is thought to reflect the recruitment of the memory trace of the face identity, was found to be implicitly modulated in MCG. These results may identify a possible role for gnosic processes in face recognition deficits in AD and suggest the importance of adopting an integrated approach to the AD diagnosis while considering electrophysiological markers.

Mechanisms of face specificity - Differentiating speed and accuracy in face cognition by event-related potentials of central processing

Given the crucial role of face recognition in social life, it is hardly surprising that cognitive processes specific for faces have been identified. In previous individual differences studies, the speed (measured in easy tasks) and accuracy (difficult tasks) of face cognition (FC, involving perception and recognition of faces) have been shown to form distinct abilities, going along with divergent factorial structures. This result has been replicated, but remained unexplained. To fill this gap, we first parameterized the sub-processes underlying speed vs. accuracy in easy and difficult memory tasks for faces and houses in a large sample. Then, we analyzed event-related potentials (ERPs) extracted from the EEG by using residue iteration decomposition (RIDE), yielding a central (C) component that is comparable to a purified P300. Structural equation modeling (SEM) was applied to estimate face specificity of C component latencies and amplitudes. If performance in easy tasks relies on purely general processes that are insensitive to stimulus content, there should be no specificity of individual differences in the latency recorded in easy tasks. However, in difficult tasks specificity was expected. Results indicated that, contrary to our predictions, specificity occurred in the C component latency of both speed-based and accuracy-based measures, but was stronger in accuracy. Further analyses suggested specific relationships between the face-related C latency and FC ability. Finally, we detected specificity in RTs of easy tasks when single tasks were modeled, but not when multiple tasks were jointly modeled. This suggests that the mechanisms leading to face specificity in performance speed are distinct across tasks.

Prior knowledge promotes hippocampal separation but cortical assimilation in the left inferior frontal gyrus

An adaptive memory system rarely learns information tabula rasa, but rather builds on prior knowledge to facilitate learning. How prior knowledge influences the neural representation of novel associations remains unknown. Here, participants associated pairs of faces in two conditions: a famous, highly familiar face with a novel face or two novel faces while undergoing fMRI. We examine multivoxel activity patterns corresponding to individual faces before and after learning. The activity patterns representing members of famous-novel pairs becomes separated in the hippocampus, that is, more distinct from one another through learning, in striking contrast to paired novel faces that become similar. In the left inferior frontal gyrus, however, prior knowledge leads to integration, and in a specific direction: the representation of the novel face becomes similar to that of the famous face after learning, suggesting assimilation of new into old memories. We propose that hippocampal separation might resolve interference between existing and newly learned information, allowing cortical assimilation. Thus, associative learning with versus without prior knowledge relies on radically different computations.

Prior knowledge strongly impacts new learning, but its influence on the neural representation of novel information is unknown. Here, the authors show multiple neural codes for learning: prior knowledge leads to integrated cortical representations, while promoting hippocampal separation.

The recovery speed of category sensitive N170 responses to faces and Chinese characters

Neural selectivity of N170 responses is important for understanding face, word, and object processing in the brain. However, the recovery times of neural selective responses remain unclear. In the present study, we used an adaptation paradigm to test the recovery speed of N170 responses to faces and Chinese characters. The findings revealed that recovery of N170 responses elicited by faces occurred between 1400 and 1800 ms after stimulus onset, whereas those elicited by Chinese characters occurred between 600 and 800 ms. These results demonstrate that N170 responses involved in the processing of faces and Chinese characters exhibit category sensitive recovery speeds.

Learning own- and other-race facial identities: Testing implicit recognition with event-related brain potentials

Exposure to varying images of the same person can encourage the formation of a representation that is sufficiently robust to allow recognition of previously unseen images of this person. While behavioural work suggests that face identity learning is harder for other-race faces, the present experiment investigated the neural correlates underlying own- and other-race face learning. Participants sorted own- and other-race identities into separate identity clusters and were further familiarised with these identities in a matching task. Subsequently, we compared event-related brain potentials (ERPs) in an implicit recognition (butterfly detection) task for learnt and previously unseen identities. We observed better sorting and matching for own- than other-race identities, and behavioural learning effects were restricted to own-race identities. Similarly, the N170 ERP component showed clear learning effects for own-race faces only. The N250, a component more closely associated with face learning was more negative for learnt than novel identities. ERP findings thus suggests a processing advantage for own-race identities at an early perceptual level whereas later correlates of identity learning were unaffected by ethnicity. These results suggest learning advantages for own-race identities, which underscores the importance of perceptual expertise in the own-race bias.

Perceptual and Semantic Phases of Face Identification Processing: A Multivariate Electroencephalography Study

Rapid identification of a familiar face requires an image-invariant representation of person identity. A varying sample of familiar faces is necessary to disentangle image-level from person-level processing. We investigated the time course of face identity processing using a multivariate electroencephalography analysis. Participants saw ambient exemplars of celebrity faces that differed in pose, lighting, hairstyle, and so forth. A name prime preceded a face on half of the trials to preactivate person-specific information, whereas a neutral prime was used on the remaining half. This manipulation helped dissociate perceptual- and semantic-based identification. Two time intervals within the post-face onset electroencephalography epoch were sensitive to person identity. The early perceptual phase spanned 110-228 msec and was not modulated by the name prime. The late semantic phase spanned 252-1000 msec and was sensitive to person knowledge activated by the name prime. Within this late phase, the identity response occurred earlier in time (300-600 msec) for the name prime with a scalp topography similar to the FN400 ERP. This may reflect a matching of the person primed in memory with the face on the screen. Following a neutral prime, the identity response occurred later in time (500-800 msec) with a scalp topography similar to the P600f ERP. This may reflect activation of semantic knowledge associated with the identity. Our results suggest that processing of identity begins early (110 msec), with some tolerance to image-level variations, and then progresses in stages sensitive to perceptual and then to semantic features.

Event-Related Potentials Reveal Evidence for Late Integration of Emotional Prosody and Facial Expression in Dynamic Stimuli: An ERP Study

The aim of the present study was to test whether multisensory interactions of emotional signals are modulated by intermodal attention and emotional valence. Faces, voices and bimodal emotionally congruent or incongruent face–voice pairs were randomly presented. The EEG was recorded while participants were instructed to detect sad emotional expressions in either faces or voices while ignoring all stimuli with another emotional expression and sad stimuli of the task irrelevant modality. Participants processed congruent sad face–voice pairs more efficiently than sad stimuli paired with an incongruent emotion and performance was higher in congruent bimodal compared to unimodal trials, irrespective of which modality was task-relevant. Event-related potentials (ERPs) to congruent emotional face–voice pairs started to differ from ERPs to incongruent emotional face–voice pairs at 180 ms after stimulus onset: Irrespectively of which modality was task-relevant, ERPs revealed a more pronounced positivity (180 ms post-stimulus) to emotionally congruent trials compared to emotionally incongruent trials if the angry emotion was presented in the attended modality. A larger negativity to incongruent compared to congruent trials was observed in the time range of 400–550 ms (N400) for all emotions (happy, neutral, angry), irrespectively of whether faces or voices were task relevant. These results suggest an automatic interaction of emotion related information.

Similar distraction, but differential suppression, for faces and non-face objects: Evidence from behaviour and event-related potentials

In everyday life we constantly experience distractions. Some distractors might be more distracting than others, for example the human face, which has been shown to be very efficient in attracting attention. Here, we employed the irrelevant-distractor paradigm (Forster & Lavie, 2016) to measure behavioural and neural distraction by completely irrelevant faces or non-faces (cars), while participants performed a letter search task that was more (high-load) or less (low-load) demanding. Under low load conditions, faces and cars equally slowed responses on trials with distractors as compared to those without. In high load conditions, neither faces nor cars were distracting. However, event-related potentials revealed larger face-sensitive N170 responses to faces than cars under both load conditions, suggesting that early face-specific processing is present even under high load. A subsequent Pd modulation between 200 and 300 ms contralateral to the distractor position, which has been linked to the active top-down suppression of lateral distractors (Hickey et al., 2009) was stronger for faces compared to cars. Overall, the EEG data indicate early face-specific processes to irrelevant faces irrespective of attentional load, coupled with stronger top-down suppression for faces. Together, these processes might reduce the influence of irrelevant face distractors on behavioural performance.

To hear or not to hear: Voice processing under visual load

Adaptation to female voices causes subsequent voices to be perceived as more male, and vice versa. This contrastive aftereffect disappears under spatial inattention to adaptors, suggesting that voices are not encoded automatically. According to Lavie, Hirst, de Fockert, and Viding (2004), the processing of task-irrelevant stimuli during selective attention depends on perceptual resources and working memory. Possibly due to their social significance, faces may be an exceptional domain: That is, task-irrelevant faces can escape perceptual load effects. Here we tested voice processing, to study whether voice gender aftereffects (VGAEs) depend on low or high perceptual (Exp. 1) or working memory (Exp. 2) load in a relevant visual task. Participants adapted to irrelevant voices while either searching digit displays for a target (Exp. 1) or recognizing studied digits (Exp. 2). We found that the VGAE was unaffected by perceptual load, indicating that task-irrelevant voices, like faces, can also escape perceptual-load effects. Intriguingly, the VGAE was increased under high memory load. Therefore, visual working memory load, but not general perceptual load, determines the processing of task-irrelevant voices.

Visual processing in patients with age-related macular degeneration performing a face detection test

PURPOSE

People with age-related macular degeneration (AMD) have difficulties in familiar face recognition and facial expression discrimination. Our aim was to evaluate the visual processing of faces in AMD patients and whether this would be improved by anti-vascular endothelial growth factor therapy. This was a prospective interventional cohort study.

PATIENTS

Twelve patients with monocular wet AMD and 6 control subjects were recruited. Face detection processes were studied using cortical event-related potentials (ERPs). Patients received 3 bevacizumab intravitreal injections to the single affected eye. At baseline and 4-6 weeks after the last injection, clinical presentation and ERPs of the face task were evaluated. Face pictures were shown as targets (16.7%) among standard pictures of pixelated faces in an oddball-type paradigm.

RESULTS

Face pictures elicited well-defined electrical components in occipital and parieto-occipital cortical areas at baseline and after treatment. The face-specific N170 component was evident in all subjects with longer peak latency in patients than in controls (170±13 vs 155±14, P=0.032). Unexpectedly, an early component reflecting unintentional prediction of perceiving a face, that is, deviance-related negativity, was present in patients and controls. Visual acuity of the affected eye seemed improved in patients from logarithm of the minimum angle of resolution 0.71 (±0.33) to 0.52 (±0.39) by 119 (±23) days without accompanying significant change in face-specific ERPs.

CONCLUSIONS

Monocular wet AMD distinctly influenced face-specific brain electrophysiological components. However, the anti-vascular endothelial growth factor treatment did not improve the binocular face detection ability. The EudraCT number of this study is 2012-000765-20.

Face identity is encoded in the duration of N170 adaptation

Previous studies assessing the involvement of the face-sensitive N170 component of the event-related potential (ERP) in the processing of face identity have shown controversial results when assessing N170 amplitude in repetition suppression (RS) designs. On the other hand, N170 adaptation is robustly associated with the inter-stimulus interval (ISI) between immediate face repetitions. Interestingly, interactions of face identity and ISI could provide valuable information on early encoding of face identity, but have not been investigated so far. We employed a repetition suppression paradigm using identical and non-identical repetitions as well as parametrically varied ISIs between 500 msec and 2,000 msec in 27 healthy subjects to investigate N170 adaptation effects. Both face identity and varying ISIs significantly influenced N170 adaptation effects, albeit with small effects sizes. Most importantly, however, face identity and ISIs strongly interacted with rapid N170 amplitude recovery in non-identical trials, but sustained N170 adaptation in identical trials. We excluded low-level sensory contributions to the N170 adaptation effect by analyzing the P1 component and by running an additional experiment employing different stimulus sizes. This specific result strongly argues in favor of neuronal sensitivity to face identity, which is primarily mirrored in the N170 temporal decay function that essentially differentiates identical and non-identical face trials. In general, taking advantage of the temporal dimension of adaptation processes, i.e., their decay over time, provides additional dissections of neuronal function into feature-specific selectivity versus non-selectivity.

Misaligned and Polarity-Reversed Faces Determine Face-specific Capacity Limits

Previous research using flanker paradigms suggests that peripheral distracter faces are automatically processed when participants have to classify a single central familiar target face. These distracter interference effects disappear when the central task contains additional anonymous (non-target) faces that load the search for the face target, but not when the central task contains additional non-face stimuli, suggesting there are face-specific capacity limits in visual processing. Here we tested whether manipulating the format of non-target faces in the search task affected face-specific capacity limits. Experiment 1 replicated earlier findings that a distracter face is processed even in high load conditions when participants looked for a target name of a famous person among additional names (non-targets) in a central search array. Two further experiments show that when targets and non-targets were faces (instead of names), however, distracter interference was eliminated under high load—adding non-target faces to the search array exhausted processing capacity for peripheral faces. The novel finding was that replacing non-target faces with images that consisted of two horizontally misaligned face-parts reduced distracter processing. Similar results were found when the polarity of a non-target face image was reversed. These results indicate that face-specific capacity limits are not determined by the configural properties of face processing, but by face parts.

Lag-length effect on repetition priming of famous and unfamiliar faces: evidence from N250r and N400

Previous event-related potentials research has reliably identified two repetition priming components in faces, the N250r and the N400, which are believed to reflect, respectively, the accessing to the stored structural representations and the semantic retrieval. However, the effect of lags longer than immediate repetition and shorter than 3 min on the two components has not been described as yet, and the interaction between lag length and familiarity is unclear. The current experiment aims to address these issues. In this experiment, famous and unfamiliar faces were represented after short, medium, or long lags, and participants were required to decide whether each face was known or not. The data showed that the frontal N250r, rather than the temporal counterpart, persisted to the medium lag case for famous faces; for unfamiliar faces, no N250r was observed. The frontal N400 was more regulated by lag length than the centroparietal counterpart. These results suggest that the frontal N250r and the frontal N400 are affected by the lag length; moreover, the former is more sensitive to the pre-experimental familiarity of faces.

Electrophysiological correlates of face-evoked person knowledge

Face recognition includes identifying a face as perceptually familiar and recollecting biographical information, or person-knowledge, associated with the face. The majority of studies examining the neural basis of face recognition have confounded these stages by comparing brain responses evoked by novel and perceptually familiar famous faces. Here, we recorded EEG in two tasks in which subjects viewed two sets of faces that were equally perceptually familiar, but which had differing levels of associated person-knowledge. Our results dissociated the effects of person-knowledge from perceptual familiarity. Faces with associated biographical information elicited a larger ∼600ms centroparietal positivity in both a passive viewing task in which subjects viewed faces without explicitly responding, and an active question-answering task in which subjects indicated whether or not they knew particular facts about the faces. In the question task only, person-knowledge was associated with a negative ERP difference over right posterior scalp over the 170-450ms interval which appeared again at long latency (>900ms).

How Distance Affects Semantic Integration in Discourse: Evidence from Event-Related Potentials

Event-related potentials were used to investigate whether semantic integration in discourse is influenced by the number of intervening sentences between the endpoints of integration. Readers read discourses in which the last sentence contained a critical word that was either congruent or incongruent with the information introduced in the first sentence. Furthermore, for the short discourses, the first and last sentence were intervened by only one sentence while for the long discourses, they were intervened by three sentences. We found that the incongruent words elicited an N400 effect for both the short and long discourses. However, a P600 effect was only observed for the long discourses, but not for the short ones. These results suggest that although readers can successfully integrate upcoming words into the existing discourse representation, the effort required for this integration process is modulated by the number of intervening sentences. Thus, discourse distance as measured by the number of intervening sentences should be taken as an important factor for semantic integration in discourse.

Brain Signals of Face Processing as Revealed by Event-Related Potentials

We analyze the functional significance of different event-related potentials (ERPs) as electrophysiological indices of face perception and face recognition, according to cognitive and neurofunctional models of face processing. Initially, the processing of faces seems to be supported by early extrastriate occipital cortices and revealed by modulations of the occipital P1. This early response is thought to reflect the detection of certain primary structural aspects indicating the presence grosso modo of a face within the visual field. The posterior-temporal N170 is more sensitive to the detection of faces as complex-structured stimuli and, therefore, to the presence of its distinctive organizational characteristics prior to within-category identification. In turn, the relatively late and probably more rostrally generated N250r and N400-like responses might respectively indicate processes of access and retrieval of face-related information, which is stored in long-term memory (LTM). New methods of analysis of electrophysiological and neuroanatomical data, namely, dynamic causal modeling, single-trial and time-frequency analyses, are highly recommended to advance in the knowledge of those brain mechanisms concerning face processing.

A familiar pattern? Semantic memory contributes to the enhancement of visuo-spatial memories

In this study we quantify for the first time electrophysiological components associated with incorporating long-term semantic knowledge with visuo-spatial information using two variants of a traditional matrix patterns task. Results indicated that the matrix task with greater semantic content was associated with enhanced accuracy and RTs in a change-detection paradigm; this was also associated with increased P300 and N400 components as well as a sustained negative slow wave (NSW). In contrast, processing of the low semantic stimuli was associated with an increased N200 and a reduction in the P300. These findings suggest that semantic content can aid in reducing early visual processing of information and subsequent memory load by unitizing complex patterns into familiar forms. The N400/NSW may be associated with the requirements for maintaining visuo-spatial information about semantic forms such as orientation and relative location. Evidence for individual differences in semantic elaboration strategies used by participants is also discussed.

Electrophysiological potentials reveal cortical mechanisms for mental imagery, mental simulation, and grounded (embodied) cognition

Grounded cognition theory proposes that cognition, including meaning, is grounded in sensorimotor processing. The mechanism for grounding cognition is mental simulation, which is a type of mental imagery that re-enacts modal processing. To reveal top-down, cortical mechanisms for mental simulation of shape, event-related potentials were recorded to face and object pictures preceded by mental imagery. Mental imagery of the identical face or object picture (congruous condition) facilitated not only categorical perception (VPP/N170) but also later visual knowledge [N3(00) complex] and linguistic knowledge (N400) for faces more than objects, and strategic semantic analysis (late positive complex) between 200 and 700 ms. The later effects resembled semantic congruity effects with pictures. Mental imagery also facilitated category decisions, as a P3 peaked earlier for congruous than incongruous (other category) pictures, resembling the case when identical pictures repeat immediately. Thus mental imagery mimics semantic congruity and immediate repetition priming processes with pictures. Perception control results showed the opposite for faces and were in the same direction for objects: Perceptual repetition adapts (and so impairs) processing of perceived faces from categorical perception onward, but primes processing of objects during categorical perception, visual knowledge processes, and strategic semantic analysis. For both imagery and perception, differences between faces and objects support domain-specificity and indicate that cognition is grounded in modal processing. Altogether, this direct neural evidence reveals that top-down processes of mental imagery sustain an imagistic representation that mimics perception well enough to prime subsequent perception and cognition. Findings also suggest that automatic mental simulation of the visual shape of faces and objects operates between 200 and 400 ms, and strategic mental simulation operates between 400 and 700 ms.

Processing of task-irrelevant natural scenes in social anxiety

In this study, by manipulating perceptual load, we investigated whether socially anxious people process task-irrelevant, non-emotional, natural scenes. When attention was directed to letters and perceptual load was low, task-irrelevant natural scenes were processed, as evidenced by repetition priming effects, in both high and low socially anxious people. In the high perceptual load condition, repetition-priming effects decreased in participants with low social anxiety, but not in those with high social anxiety. The results were the same when attention was directed to pictures of animals: even in the high perceptual load condition, high socially anxious participants processed task-irrelevant natural scenes, as evidenced by flanker effects. However, when attention was directed to pictures of people, task-irrelevant natural scenes were not processed by participants in either anxiety group, regardless of perceptual load. These results suggest that high socially anxious individuals could not inhibit task-irrelevant natural scenes under conditions of high perceptual load, except when attention was focused on people.