How Hearing works:
Hearing is one of the five senses. It is a complex process of detecting sound and attaching meaning to it. The ability to hear is critical to understanding the world around us.
The human ear is fully developed at birth and can respond to sounds that are very faint as well as sounds that are very loud.
The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.
What causes hearing loss?
Hearing loss is caused by damage to any of the parts of the ear above or by interruption to the pathway of sound through the auditory system. Congenital or hereditary hearing loss is present at birth or soon after. Acquired hearing loss is developed later in life resulting from injury, trauma or illness. When describing hearing loss, we look at three factors, the type of hearing loss, the degree of hearing loss and the configuration of the hearing loss.
Type of Hearing Loss:
Hearing loss can be categorized by which part of the auditory system is damaged. There are three basic types of hearing loss;
• Conductive Hearing Loss
Conductive hearing loss results from some disruption of the outer or middle ear system and can occur for a number or reasons including;
Conductive hearing loss can often be managed medically and requires review by a GP and/or ENT Specialist.
• Sensorineural Hearing Loss
Sensorineural hearing loss results from damage to the inner ear or neural auditory pathways and can occur for a number of reasons including;
Once damage has occurred to the inner ear or neural auditory pathway, it is usually permanent and cannot be treated medically, with one of the main management options being the use of hearing aids or assistive listening devices.
• Mixed Hearing Loss
Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.
Degrees of hearing loss:
After your hearing assessment your Audiologist will be able to accurately determine the degree of hearing loss. The severity of your hearing loss is measured in terms of its functional impact on your quality of life.
• Mild: 21–45 dB
Difficulty hearing soft speech but able to hear conversations in quiet situations.
• Moderate: 46–65 dB
Difficulty hearing normal conversational speech especially in the presence of background noise.
• Severe: 66–90 dB
Normal conversational speech is inaudible and you will rely heavily on facial cues and lip reading.
• Profound: 91 dB +
Normal conversational speech is inaudible and you will rely heavily on facial cues and lip reading. There is a big variation in the success of these clients with hearing aid fitting.
Configuration of Hearing Loss:
The configuration, or shape, of the hearing loss refers to the degree and pattern of hearing loss across the frequency range. For example, a hearing loss that only affects the high frequencies would be described as a high-frequency loss.
Other descriptors associated with the configuration of the hearing loss are;
• Bilateral versus unilateral
Bilateral means hearing loss in both ears. Unilateral means hearing loss in one ear.
• Symmetrical versus asymmetrical
Symmetrical means the hearing loss is the same in each ear. Asymmetrical means the hearing loss is different in each ear.
• Progressive versus sudden hearing loss
Progressive means that hearing loss becomes worse gradually over time. Sudden means hearing loss that happens quickly.
• Fluctuating versus stable hearing loss
Fluctuating means hearing loss that changes over time—sometimes getting better, sometimes getting worse.
Hearing Loss in Children:
Research has shown that adequate hearing in the first 6 months is essential to develop normal speech and language skills. In Queensland all babies are offered a neonatal hearing screen at birth and those who do not pass or who are at risk of hearing loss (e.g. those with a family history of hearing loss) are referred on for additional testing and monitoring. However, there are certain situations where a hearing loss may develop after the neonatal hearing screen so it’s important for families to be aware if their child is meeting listening milestones especially if they have a history of illness, trauma or infection.
Sound in the environment will elicit different responses from a baby depending on how alert they are at the time. Babies may react to soft sounds when they are in a pre-sleep state, but may show no significant response when they are awake and playing. Babies will also respond to voices, especially familiar voices, at a softer level than other environmental sounds and they also may lose interest in particular sounds and not continue to respond to sounds that are repetitive.
If you are concerned about your child’s hearing or speech and language development speak to your GP or contact Cairns Audiology Group on 07 4054 5561 for an appointment.
Listening Milestones for Babies:
From birth to 4 weeks of age babies will;
From 1 to 4 months babies will;
From 4 to 7 months babies will;