You don’t notice it because it’s probably how you’ve always heard the world. Sounds bash into your ear drums from all positions, alerting you — imperceptibly — whether the noise is coming from behind you, the side, above, or below. How do your ears and brain know where to pinpoint these sounds? Easy, binaural hearing.
Not everyone has the ability, mind you. The savvy tag-team effort performed by your ears is, by all accounts, a feat of acoustic wonder. For the hearing impaired, the brain’s normal auditory systems fail to sync the left and right ear, in some capacity. Similar to how one eye depends on the other for depth perception, both ears are necessary to create a robust picture of the sonic world around you.
Deep within your ear is a tiny spiral called a cochlea. It receives sound waves from the environment and transfers them into the tiny hairs lining the cavity, which then convert the waves into nerve impulses for the brain to interpret. Suddenly, a random pattern of sound waves is a dog barking, a snake hissing, or, in more unsettling cases, a virtual haircut.
People eligible for cochlear implants fall into one of three categories: post-lingually deaf adults, pre-lingually deaf children, or post-lingually hard of hearing people who have lost the ability due to diseases such as meningitis or CMV.
While science has made great leaps in restoring overall hearing to people lacking a cochlea, even a difference of millionths of a second can make for a confused brain, says Ruth Litovsky, director of the binaural hearing and speech lab at the University of Wisconsin at Madison.
"These people have retained the ability to perceive the microsecond difference in timing between the two ears,” Litovsky said in a news release of a 2010 study, “but current implants are not giving them that information.”