We tend to think that we hear with our ears, but we really hear with our brain – the ears are just a way for sound to get to the brain. The problem with hearing loss, any amount of hearing loss, is that it interferes with sound reaching the brain. In order for babies to develop speech and spoken language, they must be exposed to sound early and often. Babies with normal hearing are able to hear all of the speech sounds clearly and easily, and since the ears are always “on” babies are listening 24 hours a day. When a child has hearing loss, even when the hearing loss is mild or unilateral, some of the speech signal is reduced, distorted, or eliminated. If limited sound information is coming in, nerve pathways in the brain develop differently and this can limit the brain’s ability to use sound for understanding.
We are learning more about the impact of mild and unilateral hearing loss on long term development. The difficulty with mild and unilateral hearing losses is that it’s hard to see the impact of the hearing loss when children are very young; yet, this is the time that is most important for language development. Hearing is critical for the development of speech and language, and well-developed speech and language skills are the foundation for learning to read and write.
Unilateral hearing loss
Unilateral hearing loss means that a child has normal hearing in one ear and permanent hearing loss in the other ear. In years past, doctors and audiologists were taught that as long as a child had normal hearing in one ear then auditory, speech and language development would occur as expected. However, research has found that children with hearing loss in one ear are at higher risk for speech language delays and educational difficulties when compared to children with normal hearing in both ears. In a study that evaluated cognition, language and school achievement in children with unilateral hearing loss and their siblings with normal hearing in both ears, the children with unilateral hearing loss had lower language and verbal IQ scores compared to their siblings. Children with hearing loss in one ear required special education services at 3 times the rate and speech therapy at twice the rate compared to their siblings (Lieu JE 2013).
Children with unilateral hearing loss will have difficulty understanding spoken language when background noise is present and when trying to listen to soft speech or someone talking from a distance. In noisy environments or when listening to quiet speech the brain has to have a signal from both ears to understand the spoken message. Children with unilateral hearing loss can seem to have “selective hearing” since they usually understand speech well in quiet. Unilateral hearing loss also causes difficulty with sound localization, or determining the direction and distance of sound and speech.
Mild hearing loss
Mild hearing loss means that a child just starts to hear sounds when they are at a loudness level of 25 to 40 dB HL. For reference, normal hearing is defined as being able to hear sounds at loudness levels of 20 dB HL or less. Although we call 25-40 dB HL hearing loss “mild”, the impact of the hearing loss in the life of a child is significant. For speech and language to develop fully, babies and children need to hear clear speech. Babies with mild hearing loss will consistently turn to look for voices and sounds, they will babble and begin to say words, and they will follow directions if the room is quiet and the person speaking is relatively close by. However, without hearing aids, babies and children with mild hearing loss miss 25-40% of the speech sounds. For example, in the words “sign”, “time” and “fine” a child with mild hearing loss may not hear the “s”, “t”, and “f”, so he or she will hear that something was said but will have difficulty understanding. Since babies and young children are learning speech and language for the first time, they need to hear all of the sounds, all of the time. They don’t yet have a language base in their brain that they can use to “fill in the gaps”.
Children with mild hearing loss have difficulty understanding spoken communication in all situations, except when it is very quiet. Without hearing aids, speech and spoken language development will be negatively affected. One study found that children with 25 dB hearing were delayed in language by 1.2 years and those with 27-40 dB hearing were delayed by 2 years (Tharpe, 2008). Children with mild hearing loss have difficulty hearing distant speech, for example when someone is talking from more than 2-3 feet away. Much of what babies and children learn is through “overhearing” the conversations of others. This incidental listening requires the ability to hear and understand speech over a distance of more then a few feet. If hearing technology is not used, when children with mild hearing loss begin school they usually struggle because of the difficulty hearing over distance and in background noise.
Children with unilateral hearing loss and mild hearing loss use more energy trying to listen and understand speech. They have to work harder to understand. We have all had the experience of being in a noisy restaurant and trying to have a conversation with someone across the table. It’s difficult and it takes a lot of concentration. That is an example of what a child with unilateral hearing loss experiences for a significant portion of every day. For the child with mild hearing loss in both ears, the difficulties are even greater.
Hearing aids and other hearing technology
Hearing loss significantly reduces the amount of sound that is received by the ears and by the brain. Children with mild hearing loss need hearing aids to support normal speech and language development. Even if it’s difficult to see a difference with the hearing aids when children are very young, a difference is happening in brain development, language development and understanding. Children with mild hearing loss should wear their hearing aids during all waking hours. Infants and children need a great amount of listening experience to develop solid speech and language skills. In other words, children need to hear clear speech all day long so that they can learn about their world. When a child only uses the hearing aids 2-3 hours a day, he or she is only hearing clear speech 2-3 hours a day.
Most children with unilateral hearing loss do better when they use a hearing aid in the ear with hearing loss. The goal of a hearing aid is to create more equal hearing, so that the brain can receive signals from both ears. If there is little to no hearing in the ear with hearing loss, a traditional hearing aid may not be helpful but other technology, such as an FM system or a bone anchored hearing device (baha) worn on a softband, can be very helpful. Families should work with their audiologist and early intervention specialists to learn about all of the options.
Children with mild hearing loss and children with unilateral hearing loss should have regular hearing evaluations to monitor their hearing. Some hearing losses can get worse over time and sometimes unilateral hearing loss can progress to hearing loss in both ears. It is also important that the hearing aids are checked by your audiologist regularly. The hearing aids are allowing your child to learn about their world and communicate and we want to make sure that they are working optimally.
Lieu JE. Unilateral hearing loss in children: speech-language and school performance. B-ENT 2013 Suppl 21: 105-15.
Tharpe AM. Unilateral and Mild Bilateral Hearing Loss in Children: Past and Current Perspectives. Trends in Hearing 2008 :12 (1): 7-15.