Hearing

The Definition of Hearing

Hearing is one of the five senses. It is extremely important to the survival of our species. Hearing allows us to detect danger when other senses are diminished, such as at night when our vision is low. Hearing is defined as the ability to sense and process sounds in our environment. Like the other senses, hearing serves adaptable, evolutionary purposes.

What if your hearing isn't working properly? Deafness affects nearly 600,000 people in the US. Close to 30 million people aged 12 years or older experience hearing loss. Unilateral hearing loss or deafness is hearing loss in one ear. Bilateral hearing loss or deafness is hearing loss in both ears. Problems with hearing can occur anywhere within the auditory system: in the eardrum, the main nerve, or the brain stem and cortex. The two main types of hearing loss are conductive hearing loss, and sensorineural hearing loss.

Conductive hearing loss refers to hearing loss related to the outer and middle ear. This type of hearing loss can sometimes be corrected with surgery. Sensorineural hearing loss usually happens after damage to the inner ear. This is a common cause of permanent hearing loss. Presbycusis, or hearing loss related to age, is usually a sensorineural hearing loss disorder. There are many common causes of hearing loss including trauma, neurologic disease, aging, developmental disease, and more.

Fg. 1 The Outer Ear, pixabay.com

The Importance of Hearing

Hearing is essential for a whole host of social activities, and it plays an important role in keeping us safe. It is still possible to communicate with others if you are deaf, but it is definitely easier with the ability to hear sounds! Participating in team environments and maintaining relationships is more difficult without hearing, especially in environments where people do not know sign language.

Recent studies indicate that hearing loss, especially later in life, may be associated with an increased risk for dementia. Individuals with a hearing loss greater than 25 decibels (dB) were at increased risk of developing dementia, and those with moderate to severe loss are 5x more likely to develop dementia. Decibels (dB) are the units in which sound is measured. Decibels are measured in groups of 10s. An increase of 10 means a sound will be 10 times louder: 20 dB is 10 times louder than 10 dB.

The Hearing Process

The hearing process is beautifully complex. The ear's anatomical structures work together to produce hearing. The hearing process can be broken down into six steps. A problem with any of these steps can lead to hearing loss.

The Anatomy of the Ear

Before we look at the six steps of hearing, you need to know the different parts of the ear. The ear has three sections: the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna, auditory canal, and tympanic membrane. Deformities with the pinna, blockages within the auditory canals, or problems with the tympanic membrane can all cause problems with hearing.

The pinna is the ear itself, or the part of your ear that you can touch. The auditory canal is the part of the ear that extends from the hole on the outside of your ear all the way inside to the eardrum. The tympanic membrane is also known as the eardrum. This is a tight but flexible membrane that vibrates with sound.

The middle ear contains the structures necessary for conduction and amplification. In the middle ear, there are three structures called ossicles: the three bones of the middle ear. Conduction in hearing is the process of transmitting sound to be processed by the inner ear. Amplification is the process of making something louder or increasing its amplitude. When you are screaming, the sound has a high amplitude.

The inner ear is made up of the cochlea: a fluid-filled structure that resembles a snail shell. This structure takes the vibrations created by the eardrum and conducts them over to the ossicles. The ossicles then transmit the sound to the auditory nerve. Frequency relates to the pitch of a sound (how high or low it is). Someone with a low voice speaks at a low frequency, and someone with a high pitched voice speaks at a high frequency.

Fg. 2 Ear anatomy, pixabay.com

The Six Steps in the Hearing Process

Now that you know the different parts of the ear, you are ready to learn the six steps of the hearing process!

1. Sound travels from the environment into the ear canal, causing the tympanic membrane (or the eardrum) to vibrate.
2. The eardrum vibrates according to the frequency and amplitude of the sound wave.
3. The sound is sent over to the ossicles, which are the boney structures in the middle ear.
4. After the sound vibrations are transferred through the boney structures, the vibrations are picked up by the fluid in the cochlea. This causes the sound waves to travel even further into the ear.
5. Deep inside the ear, the vibrations are picked up by small specialized hair cells that line the semicircular canals. The location of each of the hair cells usually determines which kind of sound they can detect. Hair cells at one end of the cochlea can pick up higher-frequency sounds than the hair cells on the other end of the cochlea.
6. The vibrations arrive at the auditory nerve. The nerve picks up the signal and transmits it to the brain where it is processed and perceived.

Perception and Hearing

For those of us who are able to hear sounds, we are able to figure out information about our environment through hearing perception. Just being able to hear sounds isn't enough for us to make sense of them. Perception is processing the information we receive, and drawing conclusions based on that information.

After the hearing process takes place, our brain still needs to tell us what we are hearing. The transmitted vibrations travel up from the auditory nerve to the brain stem for processing. We can't know what we're hearing without our brain's perception abilities! The sound travels from the brain stem up to the thalamus and finally to the temporal lobe of the brain. The temporal lobe houses the auditory cortex.

There are certain things we can figure out about sound once it reaches the brain. First, we have the ability to figure out where the sound is coming from. We usually tell if a sound is coming from far away, up close, above, below, or behind us. This helps protect us and gives us time to react to our environment.

We can also focus on and distinguish certain sounds over others. In a busy stadium, we can easily have a conversation with the person sitting next to us, despite the near-constant background noise. In this circumstance, we are basically able to block out the noise that we don't want to hear and only focus on the noise that is important to the thing we are doing at that time.

Hearing Experiments in Psychology

Psychologists really like to study hearing. A psychological hearing experiment that involved something called the dichotic listening task demonstrated the human ability to selectively pay attention to certain sounds while ignoring others. We can ignore sounds coming into our right ear while paying attention to sounds coming into our left ear. The dichotic listening task involves listening to two different sounds in both ears and only paying attention to one.

There are two clinical tests that doctors use to detect hearing loss. They are called the Weber test and the Rinne test. Both of these tests use a vibrating tuning fork to figure out which kind of hearing loss the person is experiencing: conductive or sensorineural.

The Weber test involves using a tuning fork and asking the patient which side they hear the sound louder on. The sound will localize to a specific ear in patients with conductive or sensorineural hearing loss. No localization indicates either bilateral hearing loss, or no hearing loss. The Rinne test involves using a tuning fork and asking the patient whether the sound persists longer than it should.

Hearing is an important part of many famous psychological experiments. It plays a really important role in the study of Post-Traumatic Stress Disorder (PTSD). Loud sounds can trigger negative responses in people suffering from PTSD. In addition, certain psychotic disorders involve "hearing" things that are not really there. Studies about hearing have led to some very interesting findings!