Facial expression is a universal language. That fact has not been lost on designers of informational signs and posters, who use highly simplified faces to communicate to a broad audience without the use of words.

It's refreshing to see such emoji-based signage well done, as in the Food Safety Rating chart, shown in Figure 2. Published by the Public Health Department of King County (where I live), these signs warn customers about the food safety practices and number of violations cited for a restaurant's kitchen.  I have no quarrel with the designer's facial expression progression from Neutral, to Slightly Happy, to Very Happy, to Laughing.  It's very readable and it easily tells me which establishments to patronize, or avoid.

It doesn't take much to look sad.  Of all the emotions, sadness can be portrayed with the least facial movement.  ​I found a particularly good photograph of slight sadness in a newspaper recently, and I decided it would make a great subject for this month's blog.

The face of the young woman in Fig. 1 is obviously sad, but the marks of sadness on her face are slight enough to be reckoned in movements of a fraction of an inch.  She tugs at our heartstrings, but with so little actually going on!

The woman in Fig. 2, by contrast, has a face that is much more contorted in sorrow - the eyes, forehead, cheeks, mouth, and chin are all dramatically distorted and reconfigured; it's the way someone looks just short of weeping.  It is hardly surprising, when comparing the emotional intensity of the two women, that 100% of test-takers agreed that the woman in Fig. 2 appears more sad than Fig. 1.  100% results are not that uncommon with really strong expressions.  

Occasionally, however, subtle expressions can also receive unanimous results from test takers. Case in point, the unhappy woman in Fig. 1 tested as clearly and unambiguously as her near-crying counterpart, with 50 out of 50 random participants agreeing she was sad.  

​Extreme fear is notoriously hard to depict, both for animators and actors. 

Unlike the other cardinal expressions, good reference material for the face of terror (the level of fear I’m discussing here) is scarce. There are few candid photographs that clearly show a very frightened person. 

The reason for the lack of photographic reference is obvious – situations which are dire enough to solicit terror are fortunately rare, and rarer still are photographers who are detached enough to take useful photos.   It’s far easier to find terrific pictures of anger, sadness, joy, and even surprise.  The movies, usually a reliable source of reference material, are not particularly useful in this case, as even good actors rarely achieve a convincing configuration, as shown below.

The human face is the most mobile in the animal kingdom, infiltrated with a more complex network of muscles and nerves than any other creature, by far.  The repertory of movements that we can create is endless including, for some, wiggling the ears.  However, only a very small subset of these movements is significant in the facial expressions of emotion, and even here all of the facial changes that accompany, say, smiling or frowning are not equally important for recognition.  Most of our attention is focused on two tiny regions of the face we are pre-programmed to notice – the “Hot Spots” of the eye and mouth. 

Brains are efficient – they pay particular attention to the parts of our environment that will give us the most information for the least work.  When it comes to assessing the degree of illumination on a surface divided into shadow and light, for example, we focus on the boundary where there is the most rapid change from one to the other.  Tonal changes that occur elsewhere on the surface don’t register nearly as strongly, allowing artists to use the shadow edge to either intensify, or diminish, the amount of perceived contrast and brightness.