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 and stay safe.

Animals, including humans, have special ways to locate sounds. Our ears play a big role in this. By noticing tiny 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 process 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 use movements of their ears to help find sounds. Being able to locate sounds gives animals an advantage in finding food, staying safe, and communicating with 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 vibrate and make waves in the air or water. These waves travel to our ears, bouncing off parts of the outer ear and going down the ear canal. Inside the ear, the waves make the eardrum move. This movement shakes tiny bones in the middle ear, which then push on a special part inside the ear called the cochlea. Here, special cells change the vibrations into signals that travel through nerves to the brain, letting us hear the sound.

Neural interactions

In vertebrates, our brains have special ways to figure out where sounds come from. One important place in the brain, called the superior olivary nucleus, helps compare the time it takes for sound to reach each ear. This is like having tiny lines that measure tiny time differences.

Some brain cells are more connected to one ear than the other, which helps us tell the difference between sounds coming from the left or right. But this system has its limits, especially when there are echoes. Recent studies in small mammals have also shown that this idea might not explain everything completely.

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

Human auditory system

Sound localization is the process of figuring out where a sound is coming from. Our brains use small differences in how loud a sound is and how quickly it arrives at each ear to pinpoint 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 figure this out 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 too. 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, making 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

Since most animals have two ears, many of the ways humans locate sounds are also used by other animals. Animals use differences in the time and level of sounds reaching each ear to find where sounds come from. However, these effects change based on the size and position of the animal's head and ears.

Smaller animals, like insects, use different methods because their ears are too close together for time differences to be useful. Some animals make sounds themselves to help locate objects, similar to a form of natural sonar, called animal echolocation.

Animals with ears on the sides of their heads can use time differences for lower sound frequencies and level differences for higher frequencies to tell left from right. The lowest frequency they can locate depends on how far apart their ears are.

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

The tiny fly _Ormia ochracea has unique ears that allow it to find the direction of sounds very precisely, even though its ears are too small for time differences to be used in the usual way. Its ear drums are connected, letting it detect very small time differences.

Bi-coordinate sound localization (owls)

Most owls are active at night or dusk and hunt using their sense of sound rather than sight. Experiments have shown that owls can accurately locate the position of sounds, both side-to-side and up-and-down, which helps them find their prey.

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 with great accuracy and use 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 sensitivity. Research has shown that changes in the Prestin protein are key to the ability of these animals to hear high-frequency sounds needed for echolocation. This includes an important 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 the difference between hearing different sounds in each ear (dichotic listening) and hearing the same sound in both ears (diotic listening).

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