Universal Sense

Every day, we are beset by millions of sounds-ambient ones like the rumble of the train and the hum of air conditioner, as well as more pronounced sounds, such as human speech, music, and sirens. How do we know which sounds should startle us, which should engage us, and which should turn us off?

Why do we often fall asleep on train rides or in the car? Is there really a musical note that can make y...