Facial expressions of emotions are universal, but individual differences create a facial expression "signature" for each person. Pelig et al have examined whether there might be a unique family facial expression signature. Using two types of analyses, they show a correlation between movements of congenitally blind subjects with those of their relatives in think-concentrate, sadness, anger, disgust, joy, and surprise and provide evidence for a unique family facial expression signature. In the analysis "in-out family test," a particular movement was compared each time across subjects. Results show that the frequency of occurrence of a movement of a congenitally blind subject in his family is significantly higher than that outside of his family in think-concentrate, sadness, and anger. In the analysis "the classification test," in which congenitally blind subjects were classified to their families according to the gestalt of movements, results show 80% correct classification over the entire interview and 75% in anger. Analysis of the movements' frequencies in anger revealed a correlation between the movements' frequencies of congenitally blind individuals and those of their relatives. Pelig suggest that their study anticipates discovering genes that influence facial expressions, understanding their evolutionary significance, and elucidating repair mechanisms for syndromes lacking facial expression, such as autism.
Figure: Similar movements, described in detail in Table 2 of the paper, in born-blind participants (Left) and their sighted relatives (Right). Rows 1 and 2 show typical movements of the lips while the lips touch each other (as if chewing). Row 3 shows raising the right eyebrow only. Row 4 shows biting the lower lip while the mouth shows left asymmetry. Row 5 shows rolling the upper lip inside. In row 6 a "U" shape is created in the area between the lower lip and the chin. The chin is stretched and goes forward. The edges of the mouth are embedded and the lower lip is stretched. In row 7 the tongue protrudes and touches both lips.