Have you ever noticed that the world sounds different underwater than on land? U.S. Navy researchers say there is a good reason for that.
On land, sound travels through air conduction. This means that sound waves travel through the air, causing your eardrum to vibrate. This makes the three bones in your middle ear vibrate, which causes sensory cells in your inner ear to kick off an electrical signal that travels to your brain.
When you are underwater, however, sound bypasses your eardrum and the bones of your middle ear and travels through the mastoid bone (the bone you can feel with your fingers behind your ear) to get to the inner ear. This is called bone conduction.
Researchers have determined that bone conduction allows us to hear sounds underwater that are much higher in pitch than sounds we hear on land. In one study, participants were able to hear frequencies as high as 200,000 hertz underwater, which is ten times higher than the top frequency that people are able to hear on land (20,000 hertz if you do the math!). Scientists are not yet sure how this new information will be put to practical use, but it may be helpful to researchers who are developing new hearing aid technology.