, also known as broadband noise, is a type of noise that contains all the audible frequencies for humans. White noise is often present in our daily environment in the form of radio or television static, vacuums, fans, and air conditioner hums. When played in the background, white noise can reduce the sound difference between the environmental noise and background noise. This is like dropping a fork in a loud room as opposed to a quiet room, where we are less likely to be startled by the sound in the former. Parents have begun to use white noise, also known as infant 鈥渟leep machines鈥� (ISM), to mask environmental sounds during and improve their infant's sleep. However, while some infants might sleep better with the noise, the impact of white noise machines on their auditory development is not quite clear.
Our hearing system is highly complex and goes beyond the visible outer ear. The ear is typically divided into three sections: the outer ear, the middle ear, and the inner ear. The outer ear is responsible for the collection of sound waves. These are then transmitted through the middle ear to the inner ear which contains the organ responsible for hearing known as the Organ of Corti. The Organ of Corti is a spiral-shaped, fluid-filled structure with sensory cells known as hair cells. As the fluid in the cochlea moves, the hair cells bend back and forth which generates electrical signals that are sent to the brain through the auditory nerve.
The development of this system begins in utero and continues several years after birth. While the auditory system is functional after birth, it is not mature; newborns can discriminate speech sounds, recognize voices, and recognize their native speech, however, they have higher thresholds for detecting sounds, a lower ability to separate sounds of different frequencies, and struggle to notice consonants changes. This is thought to occur due to less efficient transmission of sound in the still-developing middle ear. After the maturing of the auditory system, school kids often struggle to use and interpret the auditory information available to them.
The vulnerability of the developing auditory system makes it particularly sensitive to loud, noisy environments. performed in rodents found that exposing rats to a continuous pure tone prevented the proper development of the auditory cortex. Once the sound was removed, the auditory cortex continued to develop, but the overall maturation of the auditory system was delayed. While these studies do not have direct implications for human development, they provide an interesting link between auditory development and noisy environments that warrants further research. In particular, they suggest that environmental noise could contribute to auditory and language- related delays in children.
While the above research does not have a direct link to the noise production of white noise machines on the development of children's auditory cortex, there have been showing white noise machines can reach a loudness of 91dB. This is above the safe limit set by noise exposure guidelines which states that workers should not be exposed to noise levels above 87dB for more than 8 hours a day; for every 3dB increase, sound exposure time should be reduced by half. Noise levels above the recommendations can contribute to noise-induced hearing loss (NIHL) in adults. In infants, whose shorter ear canal results in amplification of high-frequencies, the recommended safe exposure level is 50dB maximum over one hour and is the standard for most hospital nurseries. Alternate tested 14 different ISMs at 30cm, 100cm, and 200cm. They found that at a distance of 200cm, 13 of the 14 ISMs exceeded the 50dB limit. Therefore, it has been that white noise machines should be placed at least 30cm away from children, maximal volume should be avoided, and the time of use should be limited.
Many ISM or white noise machines fail to provide guidelines for safe use. Therefore, it is important to understand and follow noise level guidelines because when it comes to NIHL, prevention really is the best bet.
Daniela is a recent B.Sc. graduate from the program of Physiology at McGill.听She is very passionate about understanding the human body and how we can all individually adapt our daily lifestyles to improve its functioning.
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