A newborn’s ability to functionally use hearing develops with experience. Most babies are born with normal hearing. Binaural hearing (hearing in both left and right ears) allows your child to pinpoint sound with great accuracy and understand speech in a noisy background.
Newborns can localize sound accurately to their right and left sides. Eye movement or a slow head turn in the direction of the sound source can be observed if your newborn is awake, alert and quiet. Between 1 month and 4 months of age, your baby may not exhibit the same type of head-turning or orienting behavior. However, at five months, babies begin to seek the sound source. At about this age, the head turn changes from a reflexive activity (in the newborn) to a purposeful response.
Try this with your five-to six-month old: make soft sounds from behind and to one side as your baby looks straight ahead. A soft rattle shaken at ear-level or whispering the baby’s name should elicit a head turn towards the source. While we expect infants to startle when they hear very loud sounds, your baby should respond to soft sounds as well. During the first year, a baby’s ability to accurately locate sounds is refined. Your baby should look for the sources of common sounds such as the doorbell, the telephone ringing, a door opening, children playing, or a musical toy.
Babies learn to associate what they hear with people, places, objects, or events. It is important to be vigilant to critical milestones which may serve as guideposts for possible normal hearing:
- By 6 months, babies recognize speech sounds of their own language more than those of a foreign language. They recognize familiar voices, play with their own voices, engage in vocal play with parents, and experiment with multiple speech and non-speech sounds.
- By 9 months, babies demonstrate an understanding of simple words (“mommy,” “daddy,” “no,” “bye-bye”).
- By 10 months, a baby’s babbling should sound speech-like” with strings, of single syllables (“da-da-da-da”).
- By 12 months, one or more real, recognizable spoken words emerge.
- By 18 months, babies should understand simple phrases, retrieve familiar objects on command (without gestures) and point to body parts (“where’s your…” ears, nose, mouth eyes, etc.). At the same time, 18-month olds should have a spoken vocabulary of between 20-50 words and short phrases (“no more,” “go out,” “mommy/daddy up”).
- By 24 months, a toddler’s spoken vocabulary should be 200-300 words coupled with the emergence of simple sentences. Most should be understandable to adults not with the toddler on a daily basis. A toddler should be able to sit and listen to read-aloud storybooks.
- Between 3 and 5, spoken language should be used constantly to express wants, reflect emotions, convey information, and ask questions. A preschooler should understand nearly all that is said. Vocabulary grows from 1,000 to 2,000 words during this period, with words linked together in complex and meaningful sentences. All speech sounds should be clear and understandable by the end of the preschool period.