Hearing loss is one of the most common health handicapping conditions among children and adults. The hearing sense is the cornerstone upon which our unique human communication system is built.
This handicap therefore makes it very difficult for people to learn to speak a language, which impairs their ability to communicate naturally with other people. It also has a detrimental effect on personality and emotional development.
It is easy to take hearing for granted as sound is such a common part of everyday life. To be able to understand how sound is perceived by people and the processes involved in hearing and hearing losses, we should have a closer look at the anatomy of the ear.
Anatomy of the ear
The ear can primarily be divided into three parts, namely:
- the outer ear
- the middle ear
- the inner ear
The outer ear
The outer ear consists of two parts, namely the external ear or ear lobe (pinna) and the ear canal. It is the part of the ear that one can see.
The ear lobe is flexible and consists of cartilage and skin. It functions as a sound receiver.
Sounds are sent down the ear canal. There is a soft membrane or skin between the outer ear and the middle ear, called the eardrum or tympanic membrane.
The middle ear
Sound waves travelling down the ear canal cause the eardrum to vibrate. Just behind the eardrum are three very small bones – the smallest bones in the body.
The bones are called the hammer (maleus), the anvil (incus) and the stirrup (stapes). The hammer is attached to the eardrum and the stirrup to membrane between the middle and inner ear.
The vibrations of the eardrum are transferred to these tiny bones in the middle ear, which in turn cause fluid in the inner ear to move in wave patterns.
The function of the middle ear is called a transmitting function.
The inner ear
The cochlea is the most important component of the inner ear with regard to hearing sounds. Within the cochlea are located the auditory sensory elements known as hair cells. Each hair cell has a delicate series of hairs that stick up into the fluids of the cochlea.
As fluid waves travel through the cochlea, the delicate hairs on the sensory nerve endings bend, creating neural impulses in the eighth cranial nerve (nerve acoesticus). These impulses are interpreted by the brain as sounds.
The fluids of the cochlea can also be sent into motion by vibrations carried through the skull. This is called bone conduction.
Perception of sound
The main aim of the working of the ear is the perception of sound. Let use an example: If Lisa says to George: "what is the time?" George will detect that someone is talking to him. He will discriminate speech sounds from other sounds, for example an aeroplane flying past or a car hooting. He will identify that someone is asking him a question about time and he will understand the question and react by answering: "It is three o' clock".
The ability to perceive what was heard (auditory perception) plays an important role in human communication.
There are many children whose hearing is within normal limits, but give the impression that they cannot hear. These children have an auditory perceptual problem. They have difficulty detection, discriminating, identifying or understanding sounds. An inability to listen effectively can hamper communication, the development of language abilities as well as most areas of their school work.
Children with auditory perceptual (listening skills) difficulties should be helped by a speech therapist. Parents can also help their children improve their listening and language skills by means of a home programme such as the Listening and Language Home Programme.
Location of sound
A person’s brain can work out where a sound is coming from. One’s brain receives messages from both ears. The ear closest to the sound hears first. This helps your brain work out where the sound is coming from. A person who cannot hear in one ear can therefore not locate the source of the sound.