You’ll know what I mean if you’ve ever walked from a dark indoor space into a bright, sun-saturated summer day. Your whole face contracts into a kind of sun smile, or maybe a sun grimace, exposing your upper teeth, bunching your cheeks upward, and wrinkling the skin around your eyes to protect them from the excess light.
They say that the eyes are the windows to the soul. But the eyeballs themselves aren’t really the windows. If you could look at a pair of eyeballs minus the rest of the face, you’d only learn where the eyes are looking and how dilated the pupils are. For reading another person, it’s everything surrounding the eyes that matters the most. The windows to the soul are the eyelids that can narrow skeptically or open wide, the eyebrows that move and shape expressively, the sly wrinkles at the outer corners or on the bridge of the nose, the upward bunching of the cheeks—the many tensions and relaxations rioting around the center.
Ask any professional portraitist and you will be told that although the eyes are the most important part of the portrait, the eyeballs themselves are not so interesting to paint. They’re merely bluish-white ovals with a black dot and a reflection. The emotional expression, and the challenge to the painter, lies in all the subtleties crowding around the eyeballs.
It may not be a coincidence that those true windows to the soul correspond so exactly to the epicenter of the startle reflex. The startle has a side effect that has nothing to do with self-protection: It broadcasts personal information well beyond the simple fact that you are startled. The reason is that your moods and thoughts strongly influence how your startle reflex manifests itself in any given moment. As much as the reflex relies on primitive pathways through the base of the brain that evolved before any higher thought or emotion, it is nonetheless influenced by networks all throughout the brain. Emotions, attention, and expectation sift through the cerebral circuitry, affect the startle reflex, and shape the way it looks to others.
For example, startle is affected by anxiety. One decidedly unpleasant way to make people anxious in an experiment is to periodically shock them with electricity. As they’re cringing and waiting for the next shock, if they’re blasted with an unexpected loud sound, their startle reflex to that sound will be greatly exaggerated. Even if they’re subjected to less extreme irritants, like foul odors or unpleasant pictures, their startle reaction still will grow stronger. People who suffer from anxiety disorders also have a measurably enhanced startle reaction. They really are more jumpy.
Evolutionarily, the startle reflex’s variability has a monumental consequence. It’s one of those right-angle bends in evolution that makes biologists happy. Another creature, watching your startle reaction, could in principle learn a great deal about your inner state—and use that information to its advantage. Are you confident or anxious? More likely to run away, or more likely to go on the attack? Are you dominant over the people around you, or do you feel frightened by them? Your reaction to the sound of a broken twig or the unexpected touch of a fly landing on the back of your neck—just how much you crouch, and especially how much of the startle reaction flits across your face, pops out in the wrinkles around your eyes, or shows in the rising movement of your upper lip as you flash some teeth—these reactions can convey crucial psychological information to anyone watching.