DETERMINING DIRECTION: Because humans have an ear on either side of our heads, we can distinguish whether a sound is coming from the left or right by measuring the difference in arrival times of sounds at each ear. Sound coming from one direction will reach the ear farthest away about 1/500 of a second later than the closer ear, and our brains can pick up on this tiny time lag. Humans can also tell to some extent whether a sound is coming from above or below, and some can tell if a sound is in front of or behind them. With a little training, we can also tell how far away a sound might be, depending on how loud it is.
HELMET DIFFERENCES: On the battlefield, a soldier must balance his or her need for full head coverage in a helmet with the need to determine distance and direction of incoming sound. The older Personal Armor System for Ground Troops helmet provides full coverage of the head, including the ears, but limits a soldier's ability to determine sound direction. The newer Advanced Combat Helmet has been cut away around the eyes and ears, reducing the overall weight of the helmet and improving the soldier's use of his key senses of sight and sound. But there is some debate as to whether it makes soldiers more vulnerable to head wounds. Potentially, the sensors discussed in the story could bridge the gap between the two concerns, and help determine direction as well as offer the opportunity to protect the ears without inhibiting the sense of a sound's direction.
The Acoustical Society of America, the Institute of Electrical and Electronics Engineers, Inc.-USA, the National Institute for Occupational Safety and Health and the American Physical Society contributed to the information contained in the TV portion of this report.