What is Hearing Impairment
There are two main types of hearing impairment
1) Conductive hearing impairment
2) Sensori-neural hearing impairment
Conductive hearing impairment results from an obstruction or malformation of the outer or middle ear which stops sound from being conducted to the inner ear.
Sensori-neural hearing impairment results from a malfunction of the inner ear (cochlea) or the auditory nerve. In sensori-neural hearing impairment the person is unable to perceive sound.
Conductive hearing impairments are very common. Many children suffer from conductive hearing loss due to ear infections etc. It is important that these partial and temporary losses are noticed and dealt with promptly before it leads to problems with speech, reading and learning . Conductive losses resulting from malformation of the middle ear can sometimes be treated by surgery.
Sensori-neural hearing impairment is permanent and cannot be treated medically.A child having sensori-neural hearing impairment has to be fitted with hearing aids depending on the degree of hearing loss. In some cases, as advised by doctors, electrodes can also be implanted into the inner ear (cochlear implants).
Understanding Hearing Impairment
An audiogram is a picture of your hearing ability . It indicates how much your hearing capacity varies from normal hearing and how much is the hearing loss.
The banana shaped figure represents all the sounds that make up the human voice when speaking at normal conversational level.
The vertical lines in an audiogram represent pitch or frequency. It starts from the left representing a very low pitch sound and moving to the right representing a higher pitch. The most important pitches for speech are in the range of 500 to 5000 Hz(Hertz).
The horizontal lines in an audiogram represent loudness or intensity decibels. The 0dB line near the top of the audiogram represents an extremely soft sound. Each horizontal line below represents a louder sound.
Each point in an audiogram represents a different sound. For example point A represents a soft low pitch sound. Similarly point B represents a loud mid pitch sound while point C represents a soft high pitch sound.
3.3 How Hearing is Tested
The most simple way to test hearing ability is called pure tone audiometry. In this case you listen to a range of beeps and whistles (called pure tone) and you respond when you hear either by raising a finger or pressing a button. The small children are trained to pick up beads and put them in a small box when they hear.
The softest sound you are able to hear is called your threshold. The loudness at each pitch is reduced until you hear at that particular pitch. The softest sound at that particular pitch you can hear is marked on a graph. Similarly, the softest sounds at each pitch you can hear is recorded in the audiogram.
The instrument which produces pure tones is called audiometer.
Understanding the Audiogram
As explained above, with the help of an audiometer, threshold levels at each pitch are recorded separately for the right ear and the left ear in an audiogram.
In general practice, threshold levels for right ear are marked with red colour while blue colour is used for the left ear.
Now looking at the audiogram of an individual, the threshold levels (O) represents normal hearing in low frequencies and loss increasing to severe in high frequencies in right ear. While the left ear (X) has moderate to severe hearing loss.
One can obtain some information regarding an individual’s ability to hearing and speech. The banana shaped figure represents all the sounds that make up the human voice when speaking at normal conversational levels.
It is clear from this audiogram that the individual is able to hear all the low and mild speech sounds but is not able to hear the high pitch speech sounds in the right ear. The individual is not able to hear any speech sounds in the left ear.
Vowel sounds such as a,e,i,o and u tend to be lower in pitch and louder in intensity. Consonants such as s,p,t,sh, k and f tend to be higher in pitch and softer in intensity.
How well your child will understand speech depends on the degree and configuration of hearing loss.
3.5 Degree of Hearing Loss
The degree of hearing loss which hearing impaired people experience varies considerably. Mild hearing losses such as 25dB may cause difficulty in hearing and the person would benefit from a hearing aid. Persons with profound hearing loss of 95dB or more may find difficulty in learning and speaking. even with hearing aids. However, with continuous use of hearing aids, concerted efforts and lip reading, they can also lern to talk and do well in life.
The thresholds of 0-15 db are considered normal hearing in case of children. Different degrees of hearing loss are explained with the help of shaded portion in the audiogram.
3.6 The role of hearing aids
The role of hearing aid is to make sounds louder so that a person with hearing loss can listen, communicate and be able to participate fully in daily activities.
It is a small electronic device and has three basic parts : a microphone, amplifier and speaker (receiver). The hearing aid receives sounds through the microphone and sends them to the amplifier. The amplifier makes the sounds louder and the loud sounds are sent to the ears through the receiver.
Once a child’s hearing impairment is diagnosed by doctors and is advised the use of hearing aids, the same should be fitted at once, matching to his\her hearing loss.
3.7 Types of hearing aids
Hearing aids are mainly classified into three categories
- Body worn
- Behind The Ear
- In The Canal
Body worn hearing aid is worn on the body with the help of a specially stitched cloth belt. Hearing aid is kept in the pocket provided on the cloth belt and is connected with a wire to the receiver. Receiver is fitted on the ear mould which is placed in the ear. It is useful to cover hearing losses in low frequency.
Behind The Ear (BTE) aid is worn behind the ear. The BTE aid is connected with the ear mould that fits into the ear through a small tube. BTE aid is able to cover mild to profound loss and is widely used.
In The Canal (ITC) aid is of small size and shape of ear canal and fitted into the ear. In most of the cases the aid is not visible. Due to size limitation ITC aid may not be useful for profound loss. It can cover mild to severe loss.
Based upon the electronics used in the manufacture of these aids, these can be further classified into two categories Analog and Digital.
All hearing aids whether analog or digital perform the same function of increasing the loudness of sounds reaching the ears.
Analog hearing aids may not have all the features that come with advanced digital aids and as such are less expensive.
Features like reducing background noise such as sound of crowds in a restaurant or the sound of traffic movement etc.makes listening more comfortable.
Some advanced digital aids can detect very loud sounds above 90dB or so which can cause damage to whatever existing hearing a person has and cuts out these loud sounds.
Digital aids also produce a sharper, clearer sound quality than analog and give hearing professionals (audiologists) more flexibility to program hearing aid to the specific listening needs of an individual.