Facial expressions in various emotional states in congenitally blind and sighted subjects

Most of the studies comparing facial expressions of born blind and sighted persons that have been carried out up until now have involved children as subjects. Various studies claimed that the quantity and quality of facial expressions of congenitally blind persons deteriorate with increasing age. Here, we compared facial expressions of born blind and sighted individuals using adults predominantly. Facial expressions were documented in an individual interview inducing such emotions as think-concentrate, sadness, anger, disgust, joy, and surprise. Common characteristics found amongst studied individuals were: similar repertoires^* of movements over the entire interview, high-frequency and high-repertoire proportion of facial movements in concentration, sadness, and anger relative to those in disgust, joy, and surprise, similar distributions of a cumulative repertoire proportion of facial movements, and also common behavioral profiles of frequencies of facial movements in the emotional states discussed. Similar displays of eyebrow movements were found as well in concentration, sadness, and anger. Our study indicates that most tested characteristics of facial movements are common to born blind and sighted subjects, except for different cumulative mean frequencies in different emotional states, which is possibly related to the lack of visual feedback in born blind persons. Our study substantiates the hypothesis that facial expressions are innate and have important cues in the evolution of social communication.