UNILATERAL HEARING LOSS

Our ears hear and detect sound, but it is our brain that gives meaning to that sound.  It is the brain that identifies sounds and analyses their pitch, loudness and duration.  It stores previous information and helps us recognize and match sounds.  When it matches sounds, we understand what is heard.  It is important that the brain gets access to clear sounds, especially during critical early development stages, to set the foundations for the development of speech, language and literacy.

Our brain is wired to hear sounds from both ears.  Hearing with both ears is called binaural hearing.  When the brain receives sounds from both ears (binaurally) it is able to use this information to increase volume, to pinpoint the direction sounds originate from and for additional processing power.

Binaural hearing enables the brain to filter out a lot of the unwanted background noise and concentrate on what we are wanting to listen to.  Being able to filter out background noise is a skill we use a lot of the time because the majority of speech we listen to is not in perfectly quiet situations.  The brain is also able to distinguish the direction and distance of where sounds have come from (localisation).  Being able to localise sound means we can tell which direction sounds come from.  A child with a unilateral loss is likely to have problems listening in some situations because their ability to use binaural listening cues is reduced.

The brain and nerve pathways in babies have a lot of potential for development.  If your child has a hearing loss, the pathways from the ear to the brain do not get as much stimulation.  Without receiving full hearing stimulation, your baby’s auditory system may not develop the same way as it does for other children.  Hearing aids/devices will provide stimulation to your child’s auditory system.

Sound Localisation – This is the ability to find where sound is coming from. The brain works out which direction a sound comes from by detecting which ear receives the sound first.  When a person can hear with only one ear, they may have difficulty locating where a sound originated.  Your brain is also in charge of selective listening, which is more difficult without the use of a second ear.  Hearing sounds in two ears helps us to filter out unwanted noise so we can hear speech more clearly.  A person with a unilateral hearing loss is unable to easily separate the important information or sound from all the noises present in the background.  They will be better able to detect a sound if it is on the side of their better ear.

Cognitive load – This refers to the act of listening while performing other tasks, which can be complicated even for a person with normal hearing.  The more noise there is, the longer it takes the brain to focus on the sound and for the person to complete the task they are doing at the same time.  If the child is involved in an activity and also trying to listen to someone speak, they will miss a significant amount of what is being said.

Binaural summation – The brain “hears” a sound more loudly when it is perceived through both ears compared with when the same sound is perceived through only one ear.  This is because the brain reads nerves located in both ears and uses this information to process sounds, which seem louder when input from both ears is processed together.

Head shadow effect – This is when certain sounds that originate on the side of the hearing loss are lost to the listener completely.  Low frequency sounds bend around the person’s head and can usually be heard well through the other ear. High frequency sounds are not as elastic and do not bend around to the better hearing side.  Therefore, many high frequency sounds originating on the side of the hearing loss (e.g. some consonant sounds) are lost to a person with a unilateral hearing loss, resulting in their missing a significant amount of surrounding conversation.

Hearing over distance – The further away a sound is, the softer it sounds. Children with a unilateral hearing loss often have trouble hearing at a distance. While they may be able to hear speech from a distance, they may not always be able to understand what is being said.

Listening Effort – Children with a unilateral hearing loss may need to use more effort to concentrate on listening, particularly in noisy environments.  As a result, they may experience tiredness, fatigue, frustration and problems with concentrating.  This may also impact on their behaviour.

Normal hearing in one ear means that most children will hear well enough during their early years to make good progress in their speech and language development.  However, there is an increasing body of evidence that suggests that a significant proportion of children with a unilateral hearing loss may fall behind with language development and require additional educational support.  It is not possible to predict which children will need this extra support, so regular monitoring and evaluation of your child’s speech and language is recommended.

Children with a unilateral hearing loss will be able to hear well in quiet environments. However, many situations children experience are not ideal listening environments such as shopping centres, day care, school classrooms and outdoors.

Two ears are better than one.  We would recommend exploring hearing device options to give your child the very best access to sound, particularly during the early years of critical speech and language development.  Hearing devices can provide better access to sound and can improve sound localization, listening in group situations and hearing in background noise.  Early intervention and amplification may reduce the likelihood that a child will experience delays.