Facial expressions are fundamental emotional stimuli as they convey important information in social interaction. Most empirical research on facial expression processing has focused on isolated faces. But in everyday life, faces are embedded in surrounding context. For example, fearful faces always accompany with tight bodies, and happy faces appear in birthday parties more often than in sickrooms. Scenes which faces are embedded in provide typical visual context. Recently some studies attempted to investigate the influence of emotional scenes on facial expression processing. Although a few previous studies in this field demonstrated the scene effects of facial expression processing existed, the studies did not further explore the specific processing mechanism of the scene effects. Because of its excellent temporal resolution, the present study used event-related potentials (ERPs) to investigate the effects of scenes that contain different spatial frequencies on facial expression processing. Our hypothesis was that the different spatial frequencies of scenes affected facial expression processing in different ways.
Because the task-irrelevant task was used, our behavioral data was only used to evaluate the degree of attention. Accuracy of target stimuli did not show significant differences between conditions (above 90% for all conditions, ps > 0.1). Our ERP results showed that for scenes with broad-band spatial frequency, fearful faces which appeared in neutral scenes elicited larger N170 amplitudes than these faces which appeared in negative scenes in both right and left hemispheres. But the effects were not found for scenes with high and low spatial frequencies. In addition, neutral faces which appeared in neutral scenes elicited larger N170 amplitudes than the faces which appeared in negative scenes. The effects that were found for scenes with different spatial frequencies were distributed in different hemispheres. For scenes with broad-band and low spatial frequencies, the effects were distributed in the right hemisphere. But for scenes with high spatial frequency, the effects were distributed in the left hemisphere.
In conclusion, our findings demonstrated that the visual processing characteristic of the scene effects was different for different facial expressions. The scenes had an influence on fearful face processing. The scene effects which happened in early structural perceptual encoding of faces depended on broad-band spatial frequency information of scenes. And the scene effects 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 detailed edge information.