what does baby hear?

As part of best practice I frequently have to review new studies and articles related to sensory development.  Earlier this week I re read an article related to the auditory system that reminded me how important it is to educate others on some of the misinformation that is out there on baby's developing auditory system.  This is an area of particular interest to me because of working in the Neonatal Intensive Care Unit and the impact (both good and bad) sound can have. 

So here is some of the important take home messages from this review... 

Our auditory systems have a strong link to language development.  Interestingly enough not only is the auditory system related to language but also musical skills!

Our auditory systems require experience with voice and language, music, and appropriate environmental sounds during the last 10-12 weeks of in utero development.  Also, the period from here up to about 5 or 6 months of age is most critical to the development of the neurosesnsoy part of the auditory system.  This is when the hair cells of the cochlea, the axons of the auditory nerve and the neurons are tuned to receive signals of specific frequencies and intensities.   

In utero studies have shown as early as 32 weeks infant LEARNED their mother's voice or a melody and could discriminate it from others after birth.  This learning includes recognition of difference in pitch, pattern, intensity and rhythm. Learning occurs when the fetus is awake or in a quiet sleep and it has to be less than 50 decibels and they will primarily hear a voice or a music sound around the middle C.  Speech must have and be repeated but with just enough expansion and novelty added to retain interest otherwise baby habituates and loses interest.  Headphones should never be used on mother's belly directly because in utero sound is nondirectional and the sound from each earphone is additive which means the decibels the baby is exposed to are well above the recommended 50 decibels. This in turn can damage and destroy hair cells in the cochlea. And these hair cells are needed for baby to fine tune.  Fine tuning is important because they impact a baby's ability to have recognition of phoneme, speech patterns, pitch, and familiar voices.  Fine tuning during these critical periods are related to baby's development of language, self protection, or managing daily tasks.

Also sounds contribute to the memory circuits that are connected to our limbic systems which are responsible for our emotional memories.  Pleasure, joy, fear, anxiety are recorded and stored as auditory memories in the limbic system.  A baby even in utero as early as 34 weeks can distinguish different moods or emotional qualities to speech that is retained a a part of accumulated memories.  

So what's the take home message ?  If you are pregnant it is really good to talk to your baby, sing simple songs, and no headphones to the belly.  Once baby is here allow them time to continue to listen to you and other familiar voices such as your family.  Vary the sound in your voice to keep them interested but also repeat familiar words and sounds.  When giving them variety watch their face, look for their reaction.  Continue to sing them simple nursery rhymes.  

Activities for the first few months:

  • Hold a simple rattle about 1 foot away from your infant's face, allow them time to find it.  Try moving it around again about 1 foot so they will turn their head to find the sound.  This is better usually if you hide your face otherwise they may be too distracted by looking at you.  Try switching out the rattle for different ones after several times so baby doesn't habituate and lose interest
  • Approach your baby while they are on their belly or back from different sides, varying it throughout and call their name
  • Read to your baby and use different pitch when reading various parts in the book
  • When making sounds with your mouth try variance such as making kisses, blowing raspberries, clicking with your tongue, or making "bbbb" or "ch-ch" sounds
  • Narrate your day for them or point and label things around the community
  •  Simple nursery rhymes
Sarah Laryea