by Dennis A. Colucci, Au.D., M.A., FAAA
Parents are unsuspecting of the effects of noise on their child’s brain development during pregnancy and thereafter, but new research has shown that noise exposure is something not to be toyed with.
Human Hearing is a Work in Progress
In the fetal stages of development, the brain grows amazingly fast with nerve cells created at the rate of 250,000 a minute. By the 24th week of development, the hearing system is already working and by the 35th week the fetus can discriminate the differences in speech sounds such as “E” and “O”. Amazingly, within a couple of days after birth the infant can pick out the mother’s voice from others because of hearing and learning during its development in the womb.
Using microphones in the womb, scientists have shown that the fetus hears normal low tone sounds because of transmission through the fluids of the amniotic sac, in the same way whales hear across great distances in the ocean. Fetal hearing development is a gradual process that makes connections in the brain to suit the low tone rich uterine environment and the mother’s voice. After birth, sound experiences help the brain to add more tones to the infant’s memory libraries, along with speech and language. Ultimately, a network of connections to vision and the other senses link the newborn to the world. This development is responsible for normal brain function (neuroplasticity) over a lifetime and protecting the fledgling system from noise is paramount.
The Noise Problem
The fetal ear can hear normal sounds and also be over exposed to noise. Understanding how to separate out normal sound from noise exposure is accomplished using a few simple rules. Normal conversational speech between adults is at 62 dB and the mother’s voice in the womb to the fetus is delivered at 80 dB. To fetal development the loudness of the mother’s voice is necessary to train the brain, calibrate loudness, and grow those important nerve connections. The occasional high noise spike, in-utero MRI, or the acoustic stimulation test and normal daily noise has shown to have no effect. However, levels above this that are either chronic or repetitive, steady or impulsive at high levels cause the fetus to startle, change heart rhythms, increase blood pressure, create abnormal physiological changes, and if chronic, develop hearing loss, birth defects, premature birth, and abnormal social behavior after birth.
How to Measure Acceptable Sound Levels
Monitoring noise is a simple task that can be accomplished with an app on a cell phone. I use a free Sound Meter from Faber Acoustical, LLC because it allows me to measure the sound level and see the peak loudness too. I would use it on the Lp, dBC, and the Slow settings. Prolonged measurements above 80 dB or repeat ongoing peaks at 100 dB would suggest that the environment is too loud. A typical busy restaurant would fall within an allowable range, but a rock band, race car track, NFL, NBA, or other events, such as a concert, or other loud noise would be unacceptable. The simplest way to judge if noise is too loud is when at an arm’s length you need to raise your voice to a shout (80-85 dB) to be heard.
Since children do not reach adult levels of hearing perception until the age of 12, parents should continuously monitor noise from toys, iPods, MP3 players, and events far beyond those formative years in the womb.
Dennis A. Colucci, Au.D., M.A., FAAA is clinical expert and educator specializing in evaluating and treating newborn, pediatric, adult, and geriatric patients with hearing and balance disorders. Connect with Dr. Colucci by calling (949) 830-5770 or visiting hearingguy.com.