Hereditary family signature of facial expression

Abstract

Although facial expressions of emotion are universal, individual differences create a facial expression "signature" for each person; but, is there a unique family facial expression signature? Only a few family studies on the heredity of facial expressions have been performed, none of which compared the gestalt of movements in various emotional states; they compared only a few movements in one or two emotional states. No studies, to our knowledge, have compared movements of congenitally blind subjects with their relatives to our knowledge. Using two types of analyses, we 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. This study anticipates discovering genes that influence facial expressions, understanding their evolutionary significance, and elucidating repair mechanisms for syndromes lacking facial expression, such as autism.

Fig. 1.

The frequency of occurrence of a facial movement of a congenitally blind person within and outside of his family in each of the emotional states: concentration (a), sadness (b), anger (c), disgust (d), joy (e), and surprise (f). The x axis includes the facial movements that served for documenting facial expressions (see Table 2). The values of frequency in the y axis were obtained by using the in-out family test described in Methods. n = 51 (21 congenitally blind + 30 sighted subjects). Red squares, in family; blue squares, out of family.

Fig. 2.

The frequency of occurrence of a facial movement of a congenitally blind person within and outside of his family in the entire interview in three families, each including two brothers born blind (n = 6). The x axis includes the facial movements that served for documenting facial expressions (see Table 2). The values of frequency in the y axis were obtained by using the in-out family test described in Methods. Red squares, in family; blue squares, out of family.

Fig. 3.

The classification of a congenitally blind person to his family according to the facial movements' repertoire in various emotional states. Movements of seven congenitally blind subjects were compared with those of 50 individuals (facial movements of a single born-blind person were compared each time to those of 50 individuals) in six emotional states (x axis). The values of average correct classification in the y axis were obtained by using the classification test described in Methods. The y axis includes the proportion of the correct classifications of the born-blind subject to the in class, including their family, out of the number of all possible partitions into two classes (in class and out of class). which is 184,756. Error bars show standard deviations.

Fig. 4.

Similar movements in born-blind participants (Left) and their sighted relatives (Right). Movement 30 (see Table 2) in rows 1 and 2 shows typical movements of the lips while the lips touch each other (as if chewing). Movement 14 (see Table 2) in row 3 shows raising the right eyebrow only. Movement 22 (see Table 2) in row 4 shows biting the lower lip while the mouth shows left asymmetry. Movement 25 (see Table 2) in row 5 shows rolling the upper lip inside. For movement 41 (see Table 2) 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 movement 1 (see Table 2) in row 7 the tongue protrudes and touches both lips.