Sound localization

Sound localization is the amazing ability to figure out where a sound is coming from, like knowing if a bird is chirping to your left or right. This skill helps us understand our surroundings.

Animals, including humans, have special ways to locate sounds. Our ears help us do this. By noticing small differences in when a sound reaches each ear and how loud it sounds in each ear, our brains can determine where the sound is. This is part of the auditory system, which is how we hear.

Many other animals, such as birds and reptiles, also can locate sounds. They might use different methods than we do, and some can even move their ears to help find sounds. Being able to locate sounds helps animals find food, stay safe, and talk to each other.

For learning more about technologies that mimic this ability, you can read about acoustic location and 3D sound localization. And to understand more about sound itself, visit the page on sound and the auditory system.

How sound reaches the brain

Sound happens when things shake and make waves in the air or water. These waves travel to our ears. They bounce off parts of the outer ear and go down the ear canal. Inside the ear, the waves make the eardrum move. This movement shakes tiny bones in the middle ear. These bones push on a special part inside the ear called the cochlea. Here, special cells change the vibrations into signals. These signals travel through nerves to the brain, and that is how we hear the sound.

Neural interactions

In vertebrates, our brains have special ways to figure out where sounds come from. A place in the brain, called the superior olivary nucleus, helps compare how long it takes for sound to reach each ear. This helps us tell the difference between sounds coming from the left or right.

Some brain cells are more connected to one ear than the other, which also helps us know where a sound is coming from. But this system has its limits, especially with echoes. Studies in small mammals show that this idea might not explain everything.

Other brain cells can tell the difference between louder and quieter sounds in each ear, which helps us know where a sound is. Some of these cells change quickly, while others change more slowly.

Human auditory system

Sound localization is how we figure out where a sound is coming from. Our brains use small differences in how loud a sound is and how fast it arrives at each ear to find its location.

We can tell where a sound is based on its side-to-side position, up-and-down position, and how far away it is. Our ears help us by noticing tiny changes in timing and loudness between the two ears. For example, a sound coming from the right reaches the right ear a little earlier and might sound louder there. Our brains use these clues to determine where the sound is coming from.

Specific techniques with applications

This section talks about different ways to make sounds feel like they are coming from different places using special systems. One method uses special models to copy how sound travels to our ears. This makes the sound feel real and natural through headphones or speakers. This method can create a 3D sound feeling with just two signals.

Another method uses special audio tools like SRS Audio Sandbox, Spatializer Audio Lab, and Qsound Qxpander. These tools copy how our ears hear sounds from different directions using regular two-channel stereo sound. This helps make the sound feel more real and surround-like through normal speakers or headphones.

Some systems try to copy multichannel sound systems, like 5.1/7.1 surround sound, but use only two speakers instead. This is done by using special sound copying methods. However, this might not always work perfectly for larger listening areas, as the sound positions can sometimes get mixed up.

Animals

Many animals, like humans, have two ears and use them to find where sounds come from. They listen for small differences in when and how loud a sound is in each ear. But this changes depending on the size and position of the animal's head and ears.

Small animals, like insects, use other methods because their ears are too close together. Some animals make sounds to find objects, like a natural form of sonar called animal echolocation.

Animals with ears on the sides of their heads can tell left from right by timing and loudness differences. The lowest frequency they can locate depends on how far apart their ears are.

To find sounds in front, above, behind, or below, some animals use special structures near their ears. Others tilt their heads to get a better sense of where a sound is coming from.

The tiny fly Ormia ochracea has special ears that let it find the direction of sounds very precisely, even though its ears are too small for the usual timing differences.

Bi-coordinate sound localization (owls)

Many owls are active at night and hunt using their sense of sound instead of sight. They can accurately locate sounds from side to side and up and down, which helps them find their food.

Dolphins

Dolphins use echolocation to find and catch their food. They make short, high-frequency sounds and listen for the echoes to determine where objects are. Dolphins can locate sounds very accurately and have special structures in their heads to help with this.

The role of Prestin in sound localization:

The Prestin gene is important for sound localization in animals that use echolocation, like bats and dolphins. This gene helps the tiny cells in the inner ear move quickly in response to sound waves, improving hearing. Research shows that changes in the Prestin protein are important for these animals to hear high-frequency sounds needed for echolocation. This includes a change in one amino acid that differs between animals that use echolocation and those that do not.

History

The word "binaural" means "to hear with two ears" and was first used in 1859. It describes listening to sounds through both ears. In 1916, a German philosopher and psychologist named Carl Stumpf explained how we hear different sounds in each ear.

Scientists have been interested in how we hear with two ears for a long time. In 1792, William Charles Wells wrote about this idea. Later, other scientists did experiments to learn more about how we can tell where sounds come from. They used special tools to understand our hearing better.