The mood shift occurred even when the students performed a distracting task–putting metal pins into holes in a wooden board–as they listened. The distraction, it seems, created static for the high road, hampering intellectual understanding of the philosophical passage. But it did not lessen a whit how contagious the moods were: the low road stayed wide open.
One way moods differ from the grosser feeling of emotions, psychologists tell us, has to do with the ineffability of their causes: while we typically know what has triggered an outright emotion, we often find ourselves in one or another mood without knowing its source. The Würzburg experiment suggests, though, that our world may be filled with mood triggers that we fail to notice–everything from the saccharine Muzak in an elevator to the sour tone in someone's voice.
For instance, take the expressions we see on other people's faces. As Swedish researchers found, merely seeing a picture of a happy face elicits fleeting activity in the muscles that pull the mouth into a smile. Indeed, whenever we gaze at a photograph of someone whose face displays a strong emotion, like sadness, disgust, or joy, our facial muscles automatically start to mirror the other's facial expression.
This reflexive imitation opens us to subtle emotional influences from those around us, adding one lane in what amounts to a brain-to-brain bridge between people. Particularly sensitive people pick up this contagion more readily than most, though the impervious may sail through even the most toxic encounter. In either case, this transaction usually goes on undetected.
We mimic the happiness of a smiling face, pulling our own facial muscles into a subtle grin, even though we may be unaware that we have seen the smile. That mimicked slight smile might not be obvious to the naked eye, but scientists monitoring facial muscles track such emotional mirroring clearly. It's as though our face were being preset, getting ready to display the full emotion.
This mimicry has a bit of biological consequence, since our facial expressions trigger within us the feelings we display. We can stir any emotion by intentionally setting our facial muscles for that feeling: just clench a pencil in your teeth, and you will force your face into a smile, which subtly evokes a positive feeling.
Edgar Allan Poe had an intuitive grasp of this principle. He wrote: "When I wish to find out how good or how wicked anyone is, or what are his thoughts at the moment, I fashion the expression of my face, as accurately as possible, in accordance with the expression of his, and then wait to see what thoughts or sentiments arise in my own mind or heart, as if to match or correspond with the expression."
The scene: Paris, 1895. A handful of adventurous souls have ventured into an exhibition by the Lumière brothers, pioneers in photography. For the first time in history, the brothers are presenting to the public a "moving picture," a short film depicting–in utter silence–a train chugging into a station, spewing steam and charging toward the camera.
The audience's reaction: they scream in terror and duck under their seats.