This paper overviews research on facial expressions focusing on its social functions in communication. The psychological origin of facial expressions has been discussed from two perspectives: expressions triggered by internal emotional states and expressions triggered by social contexts. These perspectives can also be applied to congruent facial expressions that automatically occur when observing others facial expressions. To date, research suggests that congruent facial expressions contribute to the understanding of others emotion and regulate affiliative relationships in social contexts, such as trustworthiness. The evidence for social functions of congruent facial expressions would be a key to understanding the physiological and evolutional basis of facial expressions in communication.

The present study investigated electrodermal activity (EDA) and skin blood flow (SBF) in different facial areas during a mental arithmetic task (MA) and singing task (SONG). While MA required intensive internal attention and was supposed to be a weak task in the social context, SONG accompanied expressive behavior and was assumed to have a strong social context. EDA in the forehead, cheek, and nose; SBF in the forehead and cheek; heart rate; and normalized pulse volume were measured during the tasks. The patterns of change in each physiological response were compared between MA and SONG under non-observation and observation conditions. The results indicated no changes of facial EDA and SBF during MA in both conditions. On the other hand, increases of EDA and SBF in the forehead were indicated during SONG regardless of the presence of the observer. It was suggested that EDA and SBF in the forehead reflect the strength of the social context. The function and meaning of EDA and SBF increase in the forehead were discussed physiologically and psychophysiologically.

In this study, the physiological and psychological effect of intentional self-touching during skincare by users of cosmetics is considered. Self-touching is defined as the action where pressure is applied to the cheeks with both hands after lotion application in this study. For physiological indicators, an electrocardiogram was taken and respiration was measured, and for psychological indicators, subjective emotions were assessed. From the results of the experiment, shallow breathing increased and emotions such as “Satisfaction”, “Enjoyment”, “Vitality”, “Luxury” and “Tokimeki” occurred from self-touching after lotion application. Changes in physiological response and the arousal of subjective emotions indicated that self-touching increased outward awareness.

The present study measured blood flow to the nose tip during a concealed information test (CIT), which examines whether an examinee recognizes crime-relevant information. Twenty participants received two CITs. They recognized a crime-relevant item in one of the two CITs. The nasal blood flow was lower for the recognized crime-relevant item than for the crime-irrelevant ones. The time course of the nasal blood flow differed from that of the fingertip blood flow that is one of existing CIT indices. Furthermore, the nasal blood flow significantly discerned whether each participant recognized the crime-relevant item. These results indicate that nasal blood flow can be a new index for the CIT.