All of a sudden, you realise that the person you are talking to has stopped listening to what you are saying, and that they are now looking over your shoulder at something behind you. With a look of complete terror on their face, they raise their arm and point, with a trembling finger, to whatever it is behind you. You have not yet turned around, but already you are terrified too...
When we are frightened, that fear shows in our face. Similarly, when something disgusts us, that emotion is reflected in our facial expression. Do these facial expressions have a purpose?
A common theory in neuroscience is that facial expressions are a form of non-verbal communication, which allows others to share the emotion we are feeling. If I see that you are looking scared, then I am immediately aware that something has frightened you, and maybe I need to be alert to what the danger is as well. However for many years people have thought that there might be more to it.
In 1872 Charles Darwin published a book called 'The Expressions of the Emotions in Man and Animals.' He suggested that facial expressions of emotion did not originate in nonverbal social communication. Rather they had a functional role, as part of our preparation for perception and action. A recent article (2008) from a group of scientists at the University of Toronto supports Darwin's original idea.
Essentially the facial expression of fear enhances sensory acquisition: the brow rises, the eye-lids go up, which would suggest sensory alertness - looking harder to see any danger. This work plotted the visual-field size, and found that fear resulted in a substantially larger subjective visual field.
In addition, the retina has a small central area called the fovea, and it is only the part of the scene in front of us that falls on the fovea that is seen sharply. Vision is a complex process, which involves eye movements known as saccades. Saccades are the fastest movement produced by the human body! Humans scan the world that they see, using a series of saccades, in order to bring different parts of the image onto the fovea, and thus show that part of the image sharply. The process of eye movements in order to see different parts of the scene in sharp focus is known as foveation. The Canadian scientists found that under fear conditions, the process of horizontal foveation was enhanced. There is an obvious evolutionary advantage here, since it is in times of danger that our visual processes need to be at their most acute. Conversly the team found that disgust had the opposite effect - the eyes tended to be more closed, the visual-field size was smaller, and the speed of horizontal foveation decreased. Disgust can be seen as the opposite of fear, it is a situation where we want to close down our sensory acquisition, not to enhance it.
The conclusion was that expressions of fear and disgust may have originated not as a means of social communication, but rather were about us modifying our preparedness for perception and action, either sensory vigilence to enhance the detection of the source of a possible threat in the case of fear, or as a way of rejecting the sensory input in the case of disgust. Support to this idea is given by the fact that these facial expressions are remarkably similar across all cultures.
You can read the full article here.