Hearing Screening Overview
Sound has two measurable characteristics: frequency (Hertz) and volume (decibels).
Frequency (Pitch or Tone)
Frequency is the range of tones, measured in Hertz (Hz). Hertz is the international system of measurement (SI) unit of frequency or tone equal to sound wave or cycle per second. Although we can hear sounds as low as 20 Hz, we only use a very limited range (250 Hz through 8000 Hz) for our daily listening needs. Since this frequency range is critical for hearing and understanding speech and other sounds 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 6000 Hz (ages 11 and older) are used for routine hearing screening.
Volume (Intensity or Loudness)
Volume is the range of sound loudness, measured in decibels (dB). The greater the decibel number, the louder the sound. The minimal sound level that the majority of people with normal hearing can detect is 0dB. At least twenty percent of children can hear sounds as low as -10dB (Roberts & Huber, 1967). A 130dB sound causes pain in most people's ears. People usually speak at an intensity of 45-60dB (Centers for Disease Control and Prevention [CDC], June 2012).
Hearing and Hearing Loss Defined
The American Standards Association set the level of audiometric zero in 1951. Several studies in the 1960s found that about half of adults and children could hear the screening frequencies of 500, 1000, 2000 and 4000 Hz below audiometric zero (Roberts & Huber, 1967; Roberts & Bayliss, 1967). A person with normal hearing should be able to hear volumes as low as -10dB to 15dB and frequencies of 250 through 8000 Hz.
Hearing loss is when the softest or lowest decibel (16dB or more) someone can hear is louder than the sound (0 to 15dB) someone with normal hearing can hear. Refer to the Degree and Effects of Hearing Loss (PDF).
Hearing Loss Statistics
Hearing loss is one of the most common birth defects. Approximately one to three in 1000 infants are born with hearing loss (Dedhia, Kitska, Sabo, & Chi, 2013). In Minnesota, 259 babies were born in 2014 with hearing loss (Minnesota EHDI, 2015). During the 2015-2016 school year, Early Childhood Screening identified 3740 children in Minnesota ages three to five years as having potential problems with hearing (MDE, 2016). Six out of 1000 children have permanent hearing loss by age six (Choo & Meinzen-Derr, 2010). The incidence of hearing loss increases in the school age population to nine to 10 in 1000 (White, 2010). The incidence of fluctuating or temporary hearing loss in children is one in seven (American Academy of Audiology [AAA], 2011). Approximately 30 to 50 per 1000 youth have hearing loss by late adolescence (AAA, 2011).
Types of Hearing Loss
Hearing loss is either conductive or sensorineural and, depending upon the anatomical location of the loss, can be in the external, middle, or inner ear.
Conductive Hearing Loss
- Occurs in the external and/or middle ear.
- Blocks movement of sound into the ear.
- Is typically caused by: wax in the ear canal, a hole in eardrum, broken ossicles (middle ear bones), or middle ear fluid or infection.
- Can usually be treated medically or surgically; use of amplification devices such as hearing aids can help.
Sensorineural Hearing Loss
- Is a sensory problem in the inner ear, auditory nerve, or brain.
- Is the most common type of permanent hearing impairment.
- Causes include: genetics or damage to sensory nerves due to ototoxic drugs, infections, trauma, or noise.
- Is usually treated with amplification devices such as hearing aids or cochlear implants.
Combined Hearing Loss
- Involves both conductive and sensorineural hearing loss.
Causes and Effects
Causes of Congenital Hearing Loss
Results from hereditary or environmental influences before, during, or immediately following birth can cause congenital hearing loss. At least half of the causes of congenital hearing loss are associated with genetic risk factors (Kaye, 2006). The cause of about 25 percent of congenital hearing loss cases in the U.S. is unknown (CDC, 2012).
Causes of Acquired Hearing Loss
Acquired hearing loss occurs after birth, and may be temporary or permanent. Environmental infections or toxins are a common cause of infant and childhood hearing loss. Infections that can cause hearing loss include toxoplasmosis and cytomegalovirus. Ototoxic drugs that can cause hearing loss include aminoglycosides and cisplatin. Trauma to the head or ear can also cause hearing loss. Otitis media with effusion (OME), or fluid in the middle ear, is a common cause of temporary or fluctuating hearing loss. Ninety percent of children will have had OME at least once before school age (American Academy of Pediatrics [AAP], 2004). Five to ten percent of all children may have persistent OME for a year or longer. Children with persistent (chronic) OME are at risk of developing conditions that can cause permanent hearing loss.
Causes of Noise-Induced Hearing Loss (NIHL)
The effects of overexposure to loud noise can cause NIHL (CDC, 2008). NIHL can be temporary or permanent; it can result instantly from a single loud noise like a firecracker or gunshot, or can occur gradually from repeated exposure to noise. Approximately twelve and a half percent (5.2 million) of children six to 19 years of age have some level of noise-induced hearing loss (CDC, 2011). Sources of excessive noise for children include loud music, real or toy firearms, power tools, fireworks, loud toys, and loud engines such as those in snowmobiles, jet skis, motorcycles, or farm equipment (Montgomery & Fujikawa, 1992). NIHL prevalence increases significantly in late childhood and adolescence (AAA, 2011). Strong evidence exists that increases in high frequency NIHL in adolescents is the result of exposure to recreational noise. There is a wide variation in the reported incidence of NIHL in adolescents, as background noise can influence test results and make it difficult to assess.
Effects of Hearing Loss
Hearing loss affects language acquisition, speech, learning and psychosocial wellbeing. The critical time to stimulate the auditory and language brain pathways is during the first six months of life (Joint Committee on Infant Hearing [JCIH], 2007). Children with all degrees of hearing loss who receive appropriate intervention prior to six months of age can attain speech and language skills twenty to forty percent higher than their peers who receive intervention later and comparable to their hearing peers (JCIH, 2007).
A child with a hearing loss is at a greater risk for academic deficits. In school, students must be able to listen in a noisy environment, pay attention, concentrate, and interpret information. Unidentified hearing loss in the school population is associated with impairments in speech perception and social functioning, and difficulties in attention span and learning (AAA, 2011). Even mild hearing loss can significantly interfere with the reception of spoken language and educational performance. Reading success is especially dependent on the linguistic skill of interpreting information. Half of all children with hearing loss graduate from high school with a 4th grade reading level or less, unless appropriate early educational intervention occurs (Gallaudet Research Institute, 1996). In the case of NIHL, the effects of hearing loss may come on very gradually, depending on the amount of exposure to noise (Bess, Dodd-Murphy, & Parker, 1998, Daly, Hunter, & Giebink, 1999). Ongoing review of hearing and speech age-appropriate milestones, risk factors and routine hearing screening is critical for identifying hearing loss and optimizing educational outcomes (JCIH, 2007, AAA, 2011).
Joint Commission on Infant Hearing (JCIH) Position Statement (2019)
Principles and guidelines for Early Hearing Detection and Intervention programs
JCIH endorses early detection and early intervention for all infants who are, or who are at risk of being or becoming, deaf or hard of hearing. The goals of early hearing detection and intervention (EHDI) are to maximize language and communication competence, literacy development, and psychosocial well-being for children who are deaf or hard of hearing. JCIH recommends that all infants and children receive an assessment of risk indicators for hearing loss during routine medical care, consistent with the AAP/Bright Futures Recommendations for Preventative Pediatric Health Care. These risks factors are outlined and explained in the Position Statement.