It's human nature to make snap decisions about people based on appearances. We're quick to judge whether or not we find someone attractive, how old we think they might be, and if they look weary and worn, or youthful and energetic. But what are the specific facial features we focus on to make these quick calls?

In a recent study published in Ophthalmology, 47 male and female subjects viewed digital full-faced images of standard looking individuals with neutral facial expressions. The photos were uploaded to an eye-tracking system, which measured the direction and duration of their gazes. In the first part of the experiment, after five seconds of viewing each photo subjects were asked to estimate age. In the second part, subjects determined how tired they thought each person was.

Results showed that the participants looked longest at the eye region when judging both age and fatigue, and focused mainly on the brows and lower lids when doing so. Other facial regions they looked at, though not nearly as hard or for as long, were the forehead and nose. Also, subjects spent more time staring at the cheeks of those they rated as looking less tired, and more time fixated on the brows, and area between the eyebrows, of the individuals they believed to be the oldest.