Hearing

Hearing, or auditory perception, is the ability to notice sounds through an organ like the ear by sensing vibrations as regular changes in the pressure around us. This ability lets us enjoy music, understand spoken words, and stay aware of our surroundings. The study of hearing is called auditory science.

Sounds can travel through solids, liquids, or gases. Hearing is one of the five main senses that help us experience the world. When we cannot hear well or at all, it is called hearing loss.

In humans and many animals, hearing happens mainly through the auditory system. Tiny mechanical waves, called vibrations, are picked up by the ear and changed into signals that the brain can understand, especially in a part called the temporal lobe. Like touching something, hearing needs to sense how molecules move outside our bodies, making it a type of mechanosensation.

Hearing mechanism

The human hearing system has three main parts: the outer ear, the middle ear, and the inner ear.

The outer ear includes the visible part called the pinna and the ear canal, which leads to the eardrum. The pinna helps focus sound waves into the ear canal toward the eardrum, which vibrates when sound waves hit it.

The middle ear is a small air-filled space that contains three tiny bones—the malleus, incus, and stapes. These bones help move the vibrations from the eardrum to the inner ear. The middle ear also has muscles that protect the hearing system and helps move sound waves into the inner ear.

The inner ear contains a spiral-shaped tube called the cochlea, filled with fluid. Inside the cochlea, special cells called hair cells change the vibrations into signals that the brain can understand. These signals travel through the auditory nerve to the brainstem and then to the brain, where we become aware of the sounds.

Hearing tests

Hearing can be checked using special tools called audiometers. There are also tests that can measure hearing even when someone cannot respond, like during sleep. These include auditory brainstem evoked potentials, otoacoustic emissions, and electrocochleography. Thanks to new technology, many babies now get their hearing checked right after they are born.

Some phone apps can also help check hearing. They let you see how well you hear different sounds. Even though these apps might not be perfect, they can help find out if someone might have trouble hearing.

Hearing loss

There are different kinds of hearing loss, such as conductive hearing loss, sensorineural hearing loss, and mixed types. Recently, the term Aural Diversity has been used more often to talk about hearing differences in a kinder way.

Hearing loss can range from mild to profound. Mild hearing loss makes it hard to hear quiet conversations, especially in noisy places. Moderate hearing loss also makes conversations difficult without help. Severe hearing loss needs strong hearing aids, and people often use lip-reading too. Profound hearing loss means people find it very hard to hear and usually rely on lip-reading and sign language.

To help prevent hearing loss, especially from loud noises, people can use earplugs or earmuffs, and make places quieter by using materials that absorb sound. When hearing loss happens, devices like hearing aids and cochlear implants can help. Doctors called otologists and audiologists help manage hearing loss. Hearing loss has been linked to health issues like Alzheimer's disease and dementia, with more loss tied to higher risk. It is also connected to type 2 diabetes.

Hearing underwater

Humans find it harder to hear and tell where sounds are coming from underwater. But animals that live in water, like whales, seals, and fish, have special ears that help them hear sounds better in the water.

In vertebrates

Different animals can hear different sounds. Each kind of animal has its own range of sounds it can hear, both in loudness and pitch. Sound is very important for many animals to talk to each other and stay safe. Animals that talk a lot usually hear best in the same pitch range they use to communicate.

Frequency range

See also: Hearing range

Sounds that humans can hear are called audio or sonic. These sounds usually range from 20 Hz to 20,000 Hz. Sounds higher than this are called ultrasonic, and sounds lower are called infrasonic. Some bats use ultrasonic sounds to find their way while flying. Dogs can hear ultrasonic sounds, which is why "silent" dog whistles work. Snakes can feel infrasound through their jaws, and animals like whales, giraffes, dolphins, and elephants use infrasound to talk to each other. Some fish can hear better because of a special bony connection between their ears and a part of their bodies called the swim bladder. This helps fish like carp and herring hear better.

In invertebrates

Even though they don’t have ears, invertebrates have found clever ways to sense vibrations in the air, which we call “sound.” Charles Henry Turner was the first scientist to show this clearly through careful experiments with ants. He showed that ants could hear without feeling vibrations from the ground, and he thought other insects might have similar hearing abilities too.

Many insects feel sound through tiny hairs on their bodies that move with air vibrations. Some insects even have special hairs that best pick up certain sounds, like some caterpillars that can sense the buzz of wasps to stay safe. A few insects have a special part called a tympanal organ, which acts like an eardrum on their legs. These eardrums pick up sound waves, and special cells inside turn these movements into signals the brain can understand. Some flying insects can even sense the high-pitched sounds made by bats to stay away from them.