The naked truth: the face and body sensitive N170 response is enhanced for nude bodies

Recent event-related potential studies have shown that the occipitotemporal N170 component--best known for its sensitivity to faces--is also sensitive to perception of human bodies. Considering that in the timescale of evolution clothing is a relatively new invention that hides the bodily features relevant for sexual selection and arousal, we investigated whether the early N170 brain response would be enhanced to nude over clothed bodies. In two experiments, we measured N170 responses to nude bodies, bodies wearing swimsuits, clothed bodies, faces, and control stimuli (cars). We found that the N170 amplitude was larger to opposite and same-sex nude vs. clothed bodies. Moreover, the N170 amplitude increased linearly as the amount of clothing decreased from full clothing via swimsuits to nude bodies. Strikingly, the N170 response to nude bodies was even greater than that to faces, and the N170 amplitude to bodies was independent of whether the face of the bodies was visible or not. All human stimuli evoked greater N170 responses than did the control stimulus. Autonomic measurements and self-evaluations showed that nude bodies were affectively more arousing compared to the other stimulus categories. We conclude that the early visual processing of human bodies is sensitive to the visibility of the sex-related features of human bodies and that the visual processing of other people's nude bodies is enhanced in the brain. This enhancement is likely to reflect affective arousal elicited by nude bodies. Such facilitated visual processing of other people's nude bodies is possibly beneficial in identifying potential mating partners and competitors, and for triggering sexual behavior.     

Correlations of Electrophysiological Measurements with Identification Levels of Ancient Chinese Characters

Studies of event-related potential (ERP) in the human brain have shown that the N170 component can reliably distinguish among different object categories. However, it is unclear whether this is true for different identifiable levels within a single category. In the present study, we used ERP recording to examine the neural response to different identification levels and orientations (upright vs. inverted) of Chinese characters. The results showed that P1, N170, and P250 were modulated by different identification levels of Chinese characters. Moreover, time frequency analysis showed similar results, indicating that identification levels were associated with object recognition, particularly during processing of a single categorical stimulus.     

Emotional cues during simultaneous face and voice processing: electrophysiological insights

Both facial expression and tone of voice represent key signals of emotional communication but their brain processing correlates remain unclear. Accordingly, we constructed a novel implicit emotion recognition task consisting of simultaneously presented human faces and voices with neutral, happy, and angry valence, within the context of recognizing monkey faces and voices task. To investigate the temporal unfolding of the processing of affective information from human face-voice pairings, we recorded event-related potentials (ERPs) to these audiovisual test stimuli in 18 normal healthy subjects; N100, P200, N250, P300 components were observed at electrodes in the frontal-central region, while P100, N170, P270 were observed at electrodes in the parietal-occipital region. Results indicated a significant audiovisual stimulus effect on the amplitudes and latencies of components in frontal-central (P200, P300, and N250) but not the parietal occipital region (P100, N170 and P270). Specifically, P200 and P300 amplitudes were more positive for emotional relative to neutral audiovisual stimuli, irrespective of valence, whereas N250 amplitude was more negative for neutral relative to emotional stimuli. No differentiation was observed between angry and happy conditions. The results suggest that the general effect of emotion on audiovisual processing can emerge as early as 200 msec (P200 peak latency) post stimulus onset, in spite of implicit affective processing task demands, and that such effect is mainly distributed in the frontal-central region.     

Implicit Processing of the Eyes and Mouth: Evidence from Human Electrophysiology

The current study examined the time course of implicit processing of distinct facial features and the associate event-related potential (ERP) components. To this end, we used a masked priming paradigm to investigate implicit processing of the eyes and mouth in upright and inverted faces, using a prime duration of 33 ms. Two types of prime-target pairs were used: 1. congruent (e.g., open eyes only in both prime and target or open mouth only in both prime and target); 2. incongruent (e.g., open mouth only in prime and open eyes only in target or open eyes only in prime and open mouth only in target). The identity of the faces changed between prime and target. Participants pressed a button when the target face had the eyes open and another button when the target face had the mouth open. The behavioral results showed faster RTs for the eyes in upright faces than the eyes in inverted faces, the mouth in upright and inverted faces. Moreover they also revealed a congruent priming effect for the mouth in upright faces. The ERP findings showed a face orientation effect across all ERP components studied (P1, N1, N170, P2, N2, P3) starting at about 80 ms, and a congruency/priming effect on late components (P2, N2, P3), starting at about 150 ms. Crucially, the results showed that the orientation effect was driven by the eye region (N170, P2) and that the congruency effect started earlier (P2) for the eyes than for the mouth (N2). These findings mark the time course of the processing of internal facial features and provide further evidence that the eyes are automatically processed and that they are very salient facial features that strongly affect the amplitude, latency, and distribution of neural responses to faces.     

Stimulus dependency of object-evoked responses in human visual cortex: an inverse problem for category specificity

Many studies have linked the processing of different object categories to specific event-related potentials (ERPs) such as the face-specific N170. Despite reports showing that object-related ERPs are influenced by visual stimulus features, there is consensus that these components primarily reflect categorical aspects of the stimuli. Here, we re-investigated this idea by systematically measuring the effects of visual feature manipulations on ERP responses elicited by both structure-from-motion (SFM)-defined and luminance-defined object stimuli. SFM objects elicited a novel component at 200-250 ms (N250) over parietal and posterior temporal sites. We found, however, that the N250 amplitude was unaffected by restructuring SFM stimuli into meaningless objects based on identical visual cues. This suggests that this N250 peak was not uniquely linked to categorical aspects of the objects, but is strongly determined by visual stimulus features. We provide strong support for this hypothesis by parametrically manipulating the depth range of both SFM- and luminance-defined object stimuli and showing that the N250 evoked by SFM stimuli as well as the well-known N170 to static faces were sensitive to this manipulation. Importantly, this effect could not be attributed to compromised object categorization in low depth stimuli, confirming a strong impact of visual stimulus features on object-related ERP signals. As ERP components linked with visual categorical object perception are likely determined by multiple stimulus features, this creates an interesting inverse problem when deriving specific perceptual processes from variations in ERP components.     

Spatial Attention Effects of Disgusted and Fearful Faces

Effective processing of threat-related stimuli is of significant evolutionary advantage. Given the intricate relationship between attention and the neural processing of threat-related emotions, this study manipulated attention allocation and emotional categories of threat-related stimuli as independent factors and investigated the time course of spatial-attention-modulated processing of disgusting and fearful stimuli. The participants were instructed to direct their attention either to the two vertical or to the two horizontal locations, where two faces and two houses would be presented. The task was to respond regarding the physical identity of the two stimuli at cued locations. Event-related potentials (ERP) evidences were found to support a two-stage model of attention-modulated processing of threat-related emotions. In the early processing stage, disgusted faces evoked larger P1 component at right occipital region despite the attention allocation while larger N170 component was elicited by fearful faces at right occipito-temporal region only when participants attended to houses. In the late processing stage, the amplitudes of the parietal P3 component enhanced for both disgusted and fearful facial expressions only when the attention was focused on faces. According to the results, we propose that the temporal dynamics of the emotion-by-attention interaction consist of two stages. The early stage is characterized by quick and specialized neural encoding of disgusting and fearful stimuli irrespective of voluntary attention allocation, indicating an automatic detection and perception of threat-related emotions. The late stage is represented by attention-gated separation between threat-related stimuli and neutral stimuli; the similar ERP pattern evoked by disgusted and fearful faces suggests a more generalized processing of threat-related emotions via top-down attentional modulation, based on which the defensive behavior in response to threat events is largely facilitated.     

The N170 component is sensitive to face-like stimuli: a study of Chinese Peking opera makeup

The N170 component is considered a neural marker of face-sensitive processing. In the present study, the face-sensitive N170 component of event-related potentials (ERPs) was investigated with a modified oddball paradigm using a natural face (the standard stimulus), human- and animal-like makeup stimuli, scrambled control images that mixed human- and animal-like makeup pieces, and a grey control image. Nineteen participants were instructed to respond within 1000 ms by pressing the ‘F’ or ‘J’ key in response to the standard or deviant stimuli, respectively. We simultaneously recorded ERPs, response accuracy, and reaction times. The behavioral results showed that the main effect of stimulus type was significant for reaction time, whereas there were no significant differences in response accuracies among stimulus types. In relation to the ERPs, N170 amplitudes elicited by human-like makeup stimuli, animal-like makeup stimuli, scrambled control images, and a grey control image progressively decreased. A right hemisphere advantage was observed in the N170 amplitudes for human-like makeup stimuli, animal-like makeup stimuli, and scrambled control images but not for grey control image. These results indicate that the N170 component is sensitive to face-like stimuli and reflect configural processing in face recognition.     

The Background of Reduced Face Specificity of N170 in Congenital Prosopagnosia

Congenital prosopagnosia is lifelong face-recognition impairment in the absence of evidence for structural brain damage. To study the neural correlates of congenital prosopagnosia, we measured the face-sensitive N170 component of the event-related potential in three members of the same family (father (56 y), son (25 y) and daughter (22 y)) and in age-matched neurotypical participants (young controls: n = 14; 24.5 y±2.1; old controls: n = 6; 57.3 y±5.4). To compare the face sensitivity of N170 in congenital prosopagnosic and neurotypical participants we measured the event-related potentials for faces and phase-scrambled random noise stimuli. In neurotypicals we found significantly larger N170 amplitude for faces compared to noise stimuli, reflecting normal early face processing. The congenital prosopagnosic participants, by contrast, showed reduced face sensitivity of the N170, and this was due to a larger than normal noise-elicited N170, rather than to a smaller face-elicited N170. Interestingly, single-trial analysis revealed that the lack of face sensitivity in congenital prosopagnosia is related to a larger oscillatory power and phase-locking in the theta frequency-band (4–7 Hz, 130–190 ms) as well as to a lower intertrial jitter of the response latency for the noise stimuli. Altogether, these results suggest that congenital prosopagnosia is due to the deficit of early, structural encoding steps of face perception in filtering between face and non-face stimuli.     

The habituation of event-related potentials to speech sounds and tones

We examined the short- and long-term habituation of auditory event-related potentials (ERPs) elicited by tones, complex tones and digitized speech sounds (vowels and consonant-vowel-consonant syllables). Twelve different stimuli equated in loudness and duration (300 msec) were studied. To examine short-term habituation stimuli were presented in trains of 6 with interstimulus intervals of 0.5 or 1.0 sec. The first 4 stimuli in a train were identical standards. On 50% of the trains the standard in the 5th position was replaced by a deviant probe stimulus, and on 20% of the trains the standard in the 6th position was replaced by a target, a truncated standard that required a speeded button press response.Short-term habituation (STH) was complete by the third stimulus in the train and resulted in amplitude decrements of 50–75% for the N1 component. STH was partially stimulus specific in that amplitudes were larger following deviant stimuli in the 5th position than following standards. STH of the N1 was more marked for speech sounds than for loudness-matched tones or complex tones at short ISI. In addition, standard and deviant stimuli that differed in phonetic structure showed more cross-habituation than did tones or complex tones that differed in frequency. This pattern of results suggests that STH is a function of the acoustic resemblance of successive stimuli.The long-term habituation (LTH) of the ERP was studied by comparing amplitudes across balanced 5.25 m stimulus blocks over the course of the experiment. Two types of LTH were observed. The N1 showed stimulus-specific LTH in that N1 amplitudes declined during the presentation of a stimulus, but returned to control levels when a different stimulus was presented in the subsequent condition. In contrast, the P3 elicited by the deviant stimuli showed non-specific LTH, being reduced across successive blocks containing different stimuli. P3s elicited by target stimuli remained stable in amplitude.     

Gender difference in N170 elicited under oddball task

Background

Some studies have reported gender differences in N170, a face-selective event-related potential (ERP) component. This study investigated gender differences in N170 elicited under oddball paradigm in order to clarify the effect of task demand on gender differences in early facial processing.

Findings

Twelve males and 10 females discriminated targets (emotional faces) from non-targets (emotionally neutral faces) under an oddball paradigm, pressing a button as quickly as possible in response to the target. Clear N170 was elicited in response to target and non-target stimuli in both males and females. However, females showed more negative amplitude of N170 in response to target compared with non-target, while males did not show different N170 responses between target and non-target.

Conclusions

The present results suggest that females have a characteristic of allocating attention at an early stage when responding to faces actively (target) compared to viewing faces passively (non-target). This supports previous findings suggesting that task demand is an important factor in gender differences in N170.     

Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex Modulates Repetition Suppression to Unfamiliar Faces: An ERP Study

Repeated visual processing of an unfamiliar face suppresses neural activity in face-specific areas of the occipito-temporal cortex. This "repetition suppression" (RS) is a primitive mechanism involved in learning of unfamiliar faces, which can be detected through amplitude reduction of the N170 event-related potential (ERP). The dorsolateral prefrontal cortex (DLPFC) exerts top-down influence on early visual processing. However, its contribution to N170 RS and learning of unfamiliar faces remains unclear. Transcranial direct current stimulation (tDCS) transiently increases or decreases cortical excitability, as a function of polarity. We hypothesized that DLPFC excitability modulation by tDCS would cause polarity-dependent modulations of N170 RS during encoding of unfamiliar faces. tDCS-induced N170 RS enhancement would improve long-term recognition reaction time (RT) and/or accuracy rates, whereas N170 RS impairment would compromise recognition ability. Participants underwent three tDCS conditions in random order at ∼72 hour intervals: right anodal/left cathodal, right cathodal/left anodal and sham. Immediately following tDCS conditions, an EEG was recorded during encoding of unfamiliar faces for assessment of P100 and N170 visual ERPs. The P3a component was analyzed to detect prefrontal function modulation. Recognition tasks were administered ∼72 hours following encoding. Results indicate the right anodal/left cathodal condition facilitated N170 RS and induced larger P3a amplitudes, leading to faster recognition RT. Conversely, the right cathodal/left anodal condition caused N170 amplitude and RTs to increase, and a delay in P3a latency. These data demonstrate that DLPFC excitability modulation can influence early visual encoding of unfamiliar faces, highlighting the importance of DLPFC in basic learning mechanisms.     

Exploring the Effects of Antisocial Personality Traits on Brain Potentials during Face Processing

Antisocial individuals are characterized to display self-determined and inconsiderate behavior during social interaction. Furthermore, recognition deficits regarding fearful facial expressions have been observed in antisocial populations. These observations give rise to the question whether or not antisocial behavioral tendencies are associated with deficits in basic processing of social cues. The present study investigated early visual stimulus processing of social stimuli in a group of healthy female individuals with antisocial behavioral tendencies compared to individuals without these tendencies while measuring event-related potentials (P1, N170). To this end, happy and angry faces served as feedback stimuli which were embedded in a gambling task. Results showed processing differences as early as 88–120 ms after feedback onset. Participants low on antisocial traits displayed larger P1 amplitudes than participants high on antisocial traits. No group differences emerged for N170 amplitudes. Attention allocation processes, individual arousal levels as well as face processing are discussed as possible causes of the observed group differences in P1 amplitudes. In summary, the current data suggest that sensory processing of facial stimuli is functionally intact but less ready to respond in healthy individuals with antisocial tendencies.     

对刺激朝向改变的自动加工:事件相关电位的证据

利用事件相关电位（ＥＲＰ）技术,探讨非注意状态的刺激朝向改变是否引起自动加工。刺激为具有一定朝向（垂直和水平各５０％）和一定空间频率（低频９０％,高频１０％）的光栅。要求被试忽略光栅朝向,对高频光栅作反应。刺激呈现时间为５０ｍｓ,刺激间隔在２５０至４５０ｍｓ之间随机变化。低频光栅刺激被分为两类,“匹配”（与前一刺激朝向相同）和“失匹配”（与前一刺激朝向不同）。结果发现,失匹配刺激比匹配刺激诱发出更大的枕区Ｐ１、更大的前额－中央区Ｎ１以及更大的前部与顶区Ｐ２,但前部与顶区的Ｎ２却更小。这些ＥＲＰｓ变化提示,视觉对非注意的刺激朝向变化进行了一定程度的自动加工;视觉通道可能存在类似听觉失匹配负波（ＭＭＮ）的、然而机制不同的自动加工成分     

Famous faces demand attention due to reduced inhibitory processing

People have particular difficulty ignoring distractors that depict faces. This phenomenon has been attributed to the high level of biological significance that faces carry. The current study aimed to elucidate the mechanism by which faces gain processing priority. We used a focused attention paradigm that tracks the influence of a distractor over time and provides a measure of inhibitory processing. Upright famous faces served as test stimuli and inverted versions of the faces as well as upright non-face objects served as control stimuli. The results revealed that although all of the stimuli elicited similar levels of distraction, only inverted distractor faces and non-face objects elicited inhibitory effects. The lack of inhibitory effects for upright famous faces provides novel evidence that reduced inhibitory processing underlies the mandatory nature of face processing.     

Attachment Patterns Trigger Differential Neural Signature of Emotional Processing in Adolescents

Background

Research suggests that individuals with different attachment patterns process social information differently, especially in terms of facial emotion recognition. However, few studies have explored social information processes in adolescents. This study examined the behavioral and ERP correlates of emotional processing in adolescents with different attachment orientations (insecure attachment group and secure attachment group; IAG and SAG, respectively). This study also explored the association of these correlates to individual neuropsychological profiles.

Methodology/Principal Findings

We used a modified version of the dual valence task (DVT), in which participants classify stimuli (faces and words) according to emotional valence (positive or negative). Results showed that the IAG performed significantly worse than SAG on tests of executive function (EF attention, processing speed, visuospatial abilities and cognitive flexibility). In the behavioral DVT, the IAG presented lower performance and accuracy. The IAG also exhibited slower RTs for stimuli with negative valence. Compared to the SAG, the IAG showed a negative bias for faces; a larger P1 and attenuated N170 component over the right hemisphere was observed. A negative bias was also observed in the IAG for word stimuli, which was demonstrated by comparing the N170 amplitude of the IAG with the valence of the SAG. Finally, the amplitude of the N170 elicited by the facial stimuli correlated with EF in both groups (and negative valence with EF in the IAG).

Conclusions/Significance

Our results suggest that individuals with different attachment patterns process key emotional information and corresponding EF differently. This is evidenced by an early modulation of ERP components’ amplitudes, which are correlated with behavioral and neuropsychological effects. In brief, attachments patterns appear to impact multiple domains, such as emotional processing and EFs.     

Early category-specific cortical activation revealed by visual stimulus inversion

Visual categorization may already start within the first 100-ms after stimulus onset, in contrast with the long-held view that during this early stage all complex stimuli are processed equally and that category-specific cortical activation occurs only at later stages. The neural basis of this proposed early stage of high-level analysis is however poorly understood. To address this question we used magnetoencephalography and anatomically-constrained distributed source modeling to monitor brain activity with millisecond-resolution while subjects performed an orientation task on the upright and upside-down presented images of three different stimulus categories: faces, houses and bodies. Significant inversion effects were found for all three stimulus categories between 70-100-ms after picture onset with a highly category-specific cortical distribution. Differential responses between upright and inverted faces were found in well-established face-selective areas of the inferior occipital cortex and right fusiform gyrus. In addition, early category-specific inversion effects were found well beyond visual areas. Our results provide the first direct evidence that category-specific processing in high-level category-sensitive cortical areas already takes place within the first 100-ms of visual processing, significantly earlier than previously thought, and suggests the existence of fast category-specific neocortical routes in the human brain.     

Analysis of event-related potentials to verbal stimuli in healthy subjects and schizophrenia patients

In 30 healthy subjects and 32 patients after the first episode of schizophrenia 19 channel-EEG was recorded during visual presentation of a random sequence of words and pseudo-words. In the first series of the experiments, subjects had to read the presented verbal stimuli, in the second series they had to press a button when seeing a word, and in the third series they were instructed to press the button when seeing a pseudo-word. We studied components N170, P300 and N400. In the group of healthy subjects, the amplitude of N170 increased to words in the situation of their relevance, which corresponds to the "recognition potential", whereas in the group of patients, the amplitude of N170 increased to pseudo-words when they were relevant. So it was a paradoxical response. The amplitude of the ERP later waves (P300 and N400) in the group of schizophrenic patients was smaller and the relevance effect was impaired when the target stimuli were pseudo-words. However, the incongruity effect consisting in an increase in N400 amplitude to a non-target stimulus remained intact in patients.     

The influence of stimulus intensity and inter-stimulus interval on the detection of pitch and loudness changes

This study illuminates processes underlying change detection for different features (detection of pitch versus loudness changes) and different amounts of attentional allocation (automatic versus attentive change detection). For this reason, the influence of important stimulus characteristics (intensity and inter-stimulus interval (ISI)) on these different types of change detection was determined. By varying intensity, it should be clarified whether these processes are mainly sensitive to the informational content of the change or to the total amount of stimulus energy. By varying ISI, it should be determined whether they are differentially sensitive to manipulations of encoding time and/or state of sensory refractoriness. Automatic change detection was indexed by the mismatch negativity (MMN), which is a component of the event-related brain potential (ERP). Attentive change detection was indexed by the N2b and P3 components of the ERP and by behavioral performance. Human subjects were presented with a high-probability standard tone and a low-probability deviant-tone, which differed from the standard tone in frequency (Experiment I) or intensity (Experiment II). In separate blocks, the intensities of the standard stimuli were of 55 and 70 dB SPL and ISIs were of 350 and 950 ms. During the first part of the experiments, subjects were engaged in silent reading, whereas they tried to discriminate deviants from standards in the second part. The MMN elicited by a frequency change was invariant to variations in intensity and ISI, whereas the MMN elicited by an intensity change was significantly modulated by both intensity and ISI. This implies functional differences between the neural traces underlying the frequency-MMN and the intensity-MMN. In addition, there were larger effects of the ISI on the N2b and P3 amplitudes as compared with the effects on the MMN amplitudes, suggesting stronger capacity limitations for attentive change detection than for automatic change detection.     

ERPs to stimuli requiring response production and inhibition: effects of age,probability and visual noise

Sixty-six normal adults ranging in age from 20 to 85 years were presented with stimuli containing explicit instructions to initiate or to inhibit a motor response (the words ‘push’ or ‘wait’). In one task, the effect of stimulus probability was investigated by varying probability between 0.25 and 0.75 for both Go and No-go stimuli. In another task, the effect of visual noise was investigated by degrading the stimuli with ampersands on half of the trials. Regression analysis was used to examine the effects of age on P3 amplitude and latency for each stimulus type. The effects of stimulus variables on P3, independent of age, were examined by standardizing each subject's data to those expected for a 20 year old.P3 latency to all stimuli and RT to Go stimuli increased with age. The latency of P3s to No-go stimuli was less sensitive to age than Go stimuli. P3 amplitude at Cz and Pz (but not Fz) diminished with age. P3s to Go stimuli were maximal at Pz and earlier than P3s to No-go stimuli. P3s to No-go stimuli were maximal at Cz. These differences between Go and No-go stimuli remained true under visual noise and probability manipulations. Visual noise prolonged the latency of Go and No-go P3. Less probable Go and No-go stimuli elicited larger and later P3s than more probable stimuli. Decreasing the probability of the No-go stimulus enhanced its central distribution.     

Interstimulus interval and auditory event-related potentials in children: evidence for multiple generators

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7–9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, `standard' and 1100 Hz rare, `deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.