Hearing is an essential part of development as it enables babies to take in information about the world around them. It stimulates brain development and is critical for language development. For this reason, it is vital to identify and address hearing difficulties as early as possible.
By the 16th week of pregnancy, the tiny bones in the baby’s ears begin to develop. By the 20th week of pregnancy, the baby begins to respond to sounds. Loud sounds may even make the baby startle or move about. By the 25th week of pregnancy, the auditory system becomes fully functional. At this point the baby is able to hear your voice when you are speaking or singing. Studies have shown that after birth, babies are able to recognize songs that were sung to them while in the womb. Unlike the visual system where actual visual experience begins after birth, the auditory system requires auditory experience with voice and language, music and meaningful environmental sounds during the last 10 to 12 weeks of fetal life.
A child is born with a mind that is open and ready to receive information through all five senses. The more information the mind receives, the better the child is able to understand and participate in the world around them. All five senses are tools for learning and communicating. However, the sense of hearing is the most critical for speech and language development. It is difficult to define “normal” hearing development when speaking about human beings as each individual develops in their own way and at their own pace. However, over the years, several researchers have been able to compile a guideline for general milestones for hearing development:
A Guideline for Hearing Developmental Milestones
At birth, babies are able to exhibit a startle reflex in response to sudden loud noises. This means that they will stiffen, quiver, blink, fan out their fingers and toes, or cry as a response. They are often sensitive to a wide range of sounds, including intonation and rhythmic cues. At birth, babies are able to recognize their mother’s voice and often prefer the sound of their mother’s voice. Sounds of different pitches have different effects on the infant. Low frequency sounds and rhythmic sounds have a calming effect.
Higher frequency sounds result in a more violent reaction. You may note an increase or decrease in sucking in response to sound.
At three months of age, babies are more aware of human speech and will begin to attend to voices. They will also start to show excitement for familiar sounds such as approaching footsteps, running bath water, etc. At this age, babies tend to awaken or quiet to the sound of their mother’s voice and will vocally respond to their mother’s voice. They begin to imitate noises as they hear them e.g. ooh, baba. Most importantly, at this stage, babies begin to localize sound by means of turning their eyes toward the general sound source. This is a great time to introduce sound-making toys; as they begin to enjoy such sounds and will listen to bells and other sound-making toys near them.
By four months of age babies start localizing sound by turning their head toward the general source of sound and they will actively search for human voices.
At 5 months of age, babies are able to localize sound more specifically. They distinguish between friendly and angry voices and react appropriately. They will stop crying or coo is response to music and become very interested in human voices. At this point, they are able to discriminate between sounds of strangers and familiar people.
By 6 months of age, babies specifically locate sound from any direction, such as the bell that is rung out of sight (downward localization develops before upward localization). They will respond to human speech by smiling or vocalizing and will turn immediately to their mother’s voice across the room. They may show evidence of response to different emotional tones in their mother’s voice. Their association of hearing with sound production is now evident, in that they repeat selected sounds that they have heard.
At 8 months of age it is expected for the baby to turn his head and shoulders toward familiar sounds, even when he cannot see what is happening. They begin to understand sounds and words in context e.g. responding to a telephone ringing, a human voice, his own name, “no-no,” “bye-bye“. It is at this point that they begin to enjoy games like pat-a-cake and peek-a-boo. They may respond with raised arms when their mother says, “Come up” and reaches toward the child.
At one year of age it is expected that the child will babble in response to human voice. His sound imitations indicate that he can hear the sounds and match them with his own sound production. He will enjoy various sounds like jingles and rhymes and show interest in environmental sounds that may even be beyond his immediate surroundings.
The child will respond to simple commands (at first, only when the command is accompanied by a gesture), such as giving a toy on request or going somewhere as directed. At this age, it is expected that the child understands an assortment of action words (verbs) such as “drink“, “go“, “come“, “give“, as well as some simple directions such as “wave bye bye.” No real understanding of questions is shown at this point.
By two years of age several hearing and communication skills have developed:
- Shows interest in the sounds of radio or TV commercials.
- Listens to reason of language.
- Listens to simple stories.
- Responds to command, “Show me the —.”
- Understands and answers simple “wh” questions, e.g. “Where is your –?”
- Responds to yes/no questions by shaking or nodding head.
- Waits in response to “just a minute.”
- Identifies five body parts.
- Understands family names by selecting appropriate pictures.
- Understands the phrase, “have sweets after lunch”
- Carries out 4 separate directions with a ball, e.g. “Give it to me.” “Put the ball on the block.”
- Repeats two numbers, letters, or words.
- Follows a direction with two critical elements.
- Comprehension of vocabulary increases to an average of 300 words.
- Responds differentially to directions involving prepositions: in, on, under.
- Understands some action words by selecting appropriate pictures.
- Understands the syntactic order of words when context, semantics, and prosody are coherent.
It is important to note whether the child progresses naturally through the different developmental stages rather than focusing on reaching a specific milestone by a specific age. Hearing and speech developmental milestones are affected by the presence of a hearing loss. Hearing loss that goes undetected in infants and young children compromises optimal overall development. This is because language and communication serve as the foundation for normal child development. Thus, delays in the acquisition of these skills affect literacy (reading and writing), academic achievement and social and personal development. Therefore, early detection of hearing loss in children has been a long standing priority both nationally and internationally. Ultimately, the earlier a hearing loss is detected, the earlier intervention can begin which increases the likelihood of optimizing the child’s potential in all developmental areas.
The first step is to ensure that all newborn babies undergo hearing screening before being discharged from hospital. Thereafter, it is essential to attend all follow-up visits with the Audiologist until “normal hearing” has been determined. Remember that hearing loss is not a visible disability and even normal hearing children may not begin talking until one and a half to two years of age. Therefore, if hearing loss is not detected through newborn hearing screening, it often goes undetected after 18 months of age, especially in children who have no medical conditions or other risk factors. Children with a hearing loss often learn to compensate for the lack of audible signals by relying on their other senses. They are very visual and will be sensitive to other informative signals around them such as changes in light as a door is opened or closed, vibrations in the floor and any movement around them. Because of this, their responses can seem quite normal, making hearing loss difficult to detect by parents. However, some of the tell-tale signs of hearing loss may include no babbling or vocal imitations by 12 months; no use of single words by 18 months of age; less than 10 single words by 24 months of age; and by 30 months the child will have fewer than a 100 words in their vocabulary which is often not intelligible to strangers and they will not combine words to form sentences.
Parents should trust their intuition if they suspect that their child may have hearing difficulties. It is best to seek the guidance of an Audiologist who will observe the child and conduct a few tests to determine the child’s hearing status. It is important to remember that a child is never too young to have their hearing tested.