The Effect Of Scene On Facial Expression Processing

Facial expressions are very important for social interaction as they convey information about people’s emotions and social intentions. Many previous studies have focused on the processing of isolated facial expressions. However, in real life, facial expressions are typically embedded in a rich context. For example, angry faces might be accompanied by clenched fists; happy faces are more frequent at weddings than at other scenes. A question not addressed thus far is whether context, which normally surrounds a facial expression, has an influence on how the face is processed. Some previous studies have attempted to investigate the influence of external context (e.g. scene, body posture, and voices), internal context (e.g. language) and abstract context (e.g. culture) on facial expression processing. However, different types of context have different processing mechanism. So the present study focused on a scene as a context which embedded a facial expression. Although a few previous studies in this field demonstrated the scene context effect of facial expression processing existed, the studies did not further explore the specific processing mechanism of the context effect. Because of its excellent temporal resolution, the present study used event-related potentials (ERPs) to investigate the time course of context effect in facial expression processing and the characteristic of context effect in visual processing. The major findings as follows:(1) When the scene was presented before the face-scene compound stimulus, the scene had an influence on facial expression processing. Specifically, emotionally incongruent face-scene compound stimuli elicited larger frontal-centro N2amplitude relative to the emotionally congruent face-scene compound stimuli. The effect happened in the post-perceptual stage of facial expression processing and reflected emotional conflict monitoring between emotional scenes and facial expressions. Because scrambled scenes did not have any influence on the processes of facial expressions, it was sure that the context effect of facial expressions did not happen due to low level physical features (e.g. color).(2) When the scenes and the facial expressions were presented together, the scenes had influences on fearful and happy faces discriminating processes. The facial expression discrimination was improved when the scene was emotionally congruent rather than incongruent with the facial expression. The behavior result showed that when fearful faces were embedded in negative scenes, the reaction time of facial expression discrimination was faster and more accurate than the faces in positive scenes. Similarly, the happy faces were discriminated faster in positive scenes than negative scenes. In addition, the ERP results showed that the LPP amplitude was sensitive to the emotional congruency between the scenes and face stimuli:the LPP was larger for emotionally congruent vs. incongruent face-scene compound stimuli. The results reflected that the influence which positive and negative scenes had on facial expression processing in explicit facial expression categorizations happened in the late processing stage. In this late processing stage motivational systems are more activated by the emotionally congruent face-scene compound stimuli than by the emotionally incongruent face-scene compound stimuli. Additionally, more attention is allocated to the emotionally congruent stimuli than to the emotionally incongruent stimuli.(3) In simultaneous processing of the scenes and the facial expressions, the scenes had influences on emotional and neutral facial expression discriminating processes. Behavior results showed that negative scenes disturbed the recognition of neutral expression. In addition, the ERP results showed that fearful faces elicited larger P1in neutral scenes than in fearful scenes. It reflected that this context effect happened in the early processing stage involved in emotional conflict detection between emotional scenes and facial expressions(4) The visual processing characteristic of the context effect was different for different facial expressions. The scenes had an influence on fearful face processing. This context effect which happened in early structural perceptual encoding of faces depended on broad-band spatial frequency information of scenes. And the context effect could happen in the task-irrelevant condition. However, the scenes had a different influence on neutral facial expression. Neutral facial expressions are less salient than fearful facial expressions. So it was easy for negative scenes to disturb the early perceptual encoding of neutral facial expressions. Additionally, this disturbance could happen in the condition in which scenes only retained coarse global information or detail edge information.