To understand the expressive range of the human face, nothing beats watching a colleague scream his head off in slow motion. When my lab began to study protective reflexes in the early 2000s, the video cameras came out and the place became a scare factory. Graduate students took to lurking in hidden corners and lunging out with Velociraptor shrieks. Sundry plastic bugs and a pair of taxidermized monkey arms found their way inside the lunch refrigerator. I confess, I once took a cow eyeball from a dissection class, wrapped it in foil, and gave it to a colleague as a chocolate truffle.

By filming the reactions and reviewing the videos frame by frame, we began to realize that the startle reflex might be an evolutionary point of origin for many of our most common human emotional expressions.

This article is adapted from Graziano’s new book.

When you look at still frames of a startle reaction, two features stand out: the pursing of skin around the eyes and the flashing of teeth. As the face scrunches, the upper lip pulls up, baring the upper teeth in a way that looks like a fleeting smile or a laugh. A lot of guesses have been floated about the purpose of this part of the movement. If you’re about to be attacked, maybe it’s good to appear as if you’re ready to bite. But a close look at the movement, especially if you measure muscle activity in the face, suggests a different function: eye protection. If you expose your teeth to bite a hamburger, you recruit a set of muscles that ring the mouth. In contrast, the startle reflex recruits muscles around the eyes and in the cheeks. The forehead is mobilized downward and the cheeks are mobilized upward, dragging the upper lip with them—and shielding …read more

Source:: The Atlantic – Best of

      

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