Xiangru Zhu

The time course of the influence of valence and arousal on the implicit processing of affective pictures.

In the current study, we investigated the time course of the implicit processing of affective pictures with an orthogonal design of valence (negative vs. positive) by arousal (low vs. high). Previous studies with explicit tasks suggested that valence mainly modulates early event-related potential (ERP) components, whereas arousal mainly modulates late components. However, in this study with an implicit task, we observed significant interactions between valence and arousal at both early and late stages over both parietal and frontal sites, which were reflected by three different ERP components: P2a (100–200 ms), N2 (200–300 ms), and P3 (300–400 ms). Furthermore, there was also a significant main effect of arousal on P2b (200–300 ms) over parieto-occipital sites. Our results suggest that valence and arousal effects on implicit affective processing are more complicated than previous ERP studies with explicit tasks have revealed.

Instructions of cooperation and competition influence the neural responses to others' pain: An ERP study.

Neural activities triggered by viewing other’s in pain have been previously reported to be modulated by various factors. How instructions of cooperation and competition can influence these activities has not been explored yet. In the current study, participants were instructed to play a game cooperatively or competitively with a partner. During the game, pictures showing an anonymous individual’s hand or foot in painful or non-painful situations were randomly presented in an oddball style. The event-related potentials (ERPs) when the participants passively observed these pictures under different instructions were compared. We found a significant interaction of Instruction × Picture on the P3 component, where only under competitive instruction did the painful pictures elicit significantly larger amplitudes than the non-painful pictures, but not under the cooperative instruction. This result indicates that the participants were more responsive to other’s pain in a competitive context than in a cooperative context.

Fearful faces evoke a larger C1 than happy faces in executive attention task: an event-related potential study.

Neural responses to negatively valenced stimuli such as fear are enhanced relative to positive or neutral stimuli, reflecting an emotional negativity bias. In the present study, high time resolution event related potential (ERP) techniques were used, to investigate whether C1, the earliest visually evoked potential, is modulated by emotional valence in the executive attention network. Subjects were instructed to respond to the expression of the face, while ignoring the content of word, in an emotional face-word Stroop task. We demonstrated modulation of C1 in response to fearful faces versus happy faces. The differentiation between detection of fearful and happy faces emerged at 60-90ms after the stimulus onset at the posterior electrode sites, and this early differentiation occurred regardless of whether the subject had viewed a congruent or incongruent trials (i.e., happy face with fear label or vice versa). The present results indicate that faces with a fearful expression capture processing resources at an early sensory processing stage.

Motivational Hierarchy in the Chinese Brain: Primacy of the Individual Self, Relational Self, or Collective Self?

According to the three-tier hierarchy of motivational potency in the self system, the self can be divided into individual self, relational self, and collective self, and individual self is at the top of the motivational hierarchy in Western culture. However, the motivational primacy of the individual self is challenged in Chinese culture, which raises the question about whether the three-tier hierarchy of motivational potency in the self system can be differentiated in the collectivist brain. The present study recorded the event-related potentials (ERPs) to evaluate brain responses when participants gambled for individual self, for a close friend (relational self), or for the class (collective self). The ERP results showed that when outcome feedback was positive, gambling for individual self evoked a larger reward positivity compared with gambling for a friend or for the class, while there is no difference between the latter two conditions. In contrast, when outcome feedback was negative, no significant effect was found between conditions. The present findings provide direct electrophysiological evidence that individual self is at the top of the three-tier hierarchy of the motivational system in the collectivist brain, which supports the classical pancultural view that individual self has motivational primacy.

Social contexts modulate neural responses in the processing of others’ pain: An event-related potential study

Two hypotheses have been proposed regarding the response that is triggered by observing others’ pain: the “empathizing hypothesis” and the “threat value of pain hypothesis.” The former suggests that observing others’ pain triggers an empathic response. The latter suggests that it activates the threat-detection system. In the present study, participants were instructed to observe pictures that showed an anonymous hand or foot in a painful or non-painful situation in a threatening or friendly social context. Event-related potentials were recorded when the participants passively observed these pictures in different contexts. We observed an interaction between context and picture in the early automatic N1 component, in which the painful pictures elicited a larger amplitude than the non-painful pictures only in the threatening context and not in the friendly context. We also observed an interaction between context and picture in the late P3 component, in which the painful pictures elicited a larger amplitude than the non-painful pictures only in the friendly context and not in the threatening context. These results indicate that specific social contexts can modulate the neural responses to observing others’ pain. The “empathic hypothesis” and “threat value of pain hypothesis” are not mutually exclusive and do not contradict each other but rather work in different temporal stages.

When your pain signifies my gain: neural activity while evaluating outcomes based on another person's pain

The overlap between pain and reward processing pathways leds researchers to hypothesize that there are interactions between them in the human brain. Two hypotheses have been proposed. The “competition hypothesis” posits that reward can reduce pain-related neural activity and vice versa. The “salience hypothesis” suggests that the motivational salience of pain and reward can be mutually reinforced. However, no study has tested these two hypotheses from temporal perspective as we know. In the present study, pictures depicted other people in painful or non-painful situations were used to indicate the valence of outcomes in a gambling task. The event-related potential results revealed an interaction between another person’s pain and outcome valence in multiple time stages. Specifically, the amplitudes of the N1 and P3 were enhanced in the win condition compared with the loss condition when the outcome was indicated by painful picture. This interactions between pain and reward support the salience hypothesis but not the competition hypothesis. The present results provide evidence from human subjects that support the salience hypothesis, which claims that observing other people’s pain can enhance the salience of reward.

The neural processing of fearful faces without attention and consciousness: An event-related potential study

To investigate whether the non-conscious processing of fearful faces exist in unattended condition, event-related potentials (ERPs) were recorded in a facial expression detection task. Participants were asked to discriminate the facial expressions (fearful or neutral) at the attended location. Unattended faces were associated with a response that was either congruent or in conflict with the response to the attended face. ERP results showed that the trials with response conflict between attended and unattended faces enhanced the amplitude of the P3 component when the neutral face was presented at attended location and the fearful face was presented at the unattended location. Our findings imply that the non-conscious fearful faces can be processed in the unattended condition.

The Motivational Hierarchy between the Personal Self and Close Others in the Chinese Brain: an ERP Study.

People base their decisions not only on their own self-interest but also on the interests of close others. Generally, the personal self has primacy in the motivational hierarchy in the Western culture. A recent study found that friends have the same motivational hierarchy as the personal self in the Eastern collectivist culture. Remaining unknown is whether the motivational hierarchy of the personal self and close others can be manifested in the collectivist brain. In the present study, we asked participants to gamble for the personal self, close others (i.e., mother, father, and close friend), and strangers. The positive-going deflection of event-related potentials (ERPs) in response to positive feedback showed the following pattern: personal self = mother = father > friend > stranger. In the loss condition, no significant beneficiary effect was observed. The present results indicate that the personal self and parents are intertwined in the motivational system in the Chinese undergraduate student brain, supporting the view that the personal self and parents have the same motivational primacy at the electrocortical level.

Working memory load modulates the neural response to other’s pain: Evidence from an ERP study

The present study investigated the time course of processing others pain under different conditions of working memory (WM) load. Event-related potentials (ERPs) were recorded while the participants held two digits (low WM load) or six digits (high WM load) in WM and viewed pictures that showed others who were in painful or non-painful situations. Robust WM-load×Picture interactions were found for the N2 and LPP components. In the high WM-load condition, painful pictures elicited significantly larger amplitudes than non-painful pictures. In the low WM load condition, the difference between the painful and non-painful pictures was not significant. These ERP results indicate that WM load can influence both the early automatic N2 component and late cognitive LPP component. Compared with high WM load, low WM load reduced affective arousal and emotional sharing in response to others pain and weakened the cognitive evaluation of task irrelevant stimuli. These findings are explained from the load theory perspective.

The Impact of Perceptual Load on the Non-Conscious Processing of Fearful Faces

Emotional stimuli can be processed without consciousness. In the current study, we used event-related potentials (ERPs) to assess whether perceptual load influences non-conscious processing of fearful facial expressions. Perceptual load was manipulated using a letter search task with the target letter presented at the fixation point, while facial expressions were presented peripherally and masked to prevent conscious awareness. The letter string comprised six letters (X or N) that were identical (low load) or different (high load). Participants were instructed to discriminate the letters at fixation or the facial expression (fearful or neutral) in the periphery. Participants were faster and more accurate at detecting letters in the low load condition than in the high load condition. Fearful faces elicited a sustained positivity from 250 ms to 700 ms post-stimulus over fronto-central areas during the face discrimination and low-load letter discrimination conditions, but this effect was completely eliminated during high-load letter discrimination. Our findings imply that non-conscious processing of fearful faces depends on perceptual load, and attentional resources are necessary for non-conscious processing.