Facial expression
They are a primary means of conveying social information between humans, but they also occur in most other mammals and some other animal species.
Conversely, involuntary facial expressions are believed to be innate and follow a subcortical route in the brain.
These muscles move the skin, creating lines and folds and causing the movement of facial features, such as the mouth and eyebrows.
The temporalis, masseter, and internal and external pterygoid muscles, which are mainly used for chewing, have a minor effect on expression as well.
Voluntary expression travels from the primary motor cortex through the pyramidal tract, specifically the corticobulbar projections.
This is demonstrated in infants before the age of two; they display distress, disgust, interest, anger, contempt, surprise, and fear.
[1] The lower portions of the face are controlled by the opposite cerebral hemisphere, causing asymmetric facial expression.
Functional imaging studies have found that when shown pictures of faces, there is a large increase in the activity of the amygdala.
[7] More than anything though, what shapes a child's cognitive ability to detect facial expression is being exposed to it from the time of birth.
[8][full citation needed] In addition, gender affects the tendency to express, perceive, remember, and forget specific emotions.
Research by Boston College professor Joe Tecce suggests that stress levels are revealed by blink rates.
[16] Though Tecce's data is interesting, it is important to recognize that non-verbal communication is multi-channeled, and focusing on only one aspect is reckless.
Some have hypothesized that this is due to infancy, as humans are one of the few mammals who maintain regular eye contact with their mother while nursing.
Certain Asian cultures can perceive direct eye contact as a way to signal competitiveness, which in many situations may prove to be inappropriate.
Facial expression is also used in sign languages to show adverbs and adjectives such as distance or size: an open mouth, squinted eyes and tilted back head indicate something far while the mouth pulled to one side and the cheek held toward the shoulder indicate something close, and puffed cheeks mean very large.
[22] The universality hypothesis is the assumption that certain facial expressions and face-related acts or events are signals of specific emotions (happiness with laughter and smiling, sadness with tears, anger with a clenched jaw, fear with a grimace, or gurn, surprise with raised eyebrows and wide eyes along with a slight retraction of the ears, and disgust with a wrinkled nose and squinted eyes—emotions which frequently lack the social component of those like shame, pride, jealousy, envy, deference, etc.)
To demonstrate his universality hypothesis, Ekman ran a test on a group of the South Fore people of New Guinea, a pre-industrial culture that was isolated from the West.
The experiment participants were told brief stories about emotional events (happiness, sadness, anger, fear, surprise, and disgust).
Subsequent cross-cultural studies found similar results[30] Both sides of this debate agree that the face expresses emotion.
Darwin believed that expressions were unlearned and innate in human nature and were therefore evolutionarily significant for survival.
[38] Of course, differences between the species' physical facial properties, such as white sclera and everted lips in chimps, would mean that some expressions could not be compared.
Darwin deduced that some animals communicated feelings of different emotional states with specific facial expressions.
