Peggy B. Nelson -
Division of Otolaryngology
University of Maryland School of Medicine
16 S. Eutaw Street, Suite 500
Baltimore, MD 21201
Presented Tuesday afternoon, June 17, 1997
133rd ASA Meeting, State College, PA
Embargoed until June 17, 1997
Childhood hearing loss is a widespread problem with significant impact. Hearing loss is an invisible condition resulting in communication problems that can ultimately interfere with learning and social development. Every school in the U.S. can expect to have children with permanent hearing loss. Every teacher in the early grades can expect that every day there is a child in that classroom who has trouble hearing.
Many children have hearing loss that fluctuates due to recurring ear infections. Ear infections (otitis media, or OM) constitute the most frequent medical diagnosis for children.1 The number of cases of OM has risen dramatically over the past ten years. The National Center for Health Care Statistics estimates that annually there are 70 OM cases for every 100 children under the age of 5 years. Surprisingly, even older children still experience bouts of OM; there are 14 cases annually for every 100 children ages 5 - 17. Ear infections result in hearing loss that ranges from very slight to moderate, and averages approximately 20 dB. A 20 dB decrease in hearing level is significant for learning.
Additionally, 2% of children have permanent hearing losses from damage to the inner ear/auditory nerve due to illness, heredity, head trauma, complications at birth, and other causes. The incidence of these inner ear/nerve (sensorineural) losses has also increased. The national health survey reported a 12% increase in children with hearing trouble between 1971 and 1991.2 Sensorineural hearing losses often cause damage to the high frequency regions of hearing, resulting in a muffled sound to speech, and reducing speech understanding, even for loud voices.
In addition to decreasing the intensity of incoming sounds, damage to the inner ear causes a further reduction in the ear's ability for fine-tuning to frequency and temporal changes.
Hearing loss can cause significant educational and social problems. Academic delays occur in children with even mild hearing loss as early as first grade. In later grades, two- to three-year academic delays are commonly reported. While many children with otitis media who receive good speech and language stimulation catch up to their peers, those children without sufficient intervention from teachers and families and those with sensorineural hearing loss usually do not.
Traditional classrooms are noisy, and noise interferes with all children's performance. In many classrooms, for the child in the middle of the room, the noise is as loud as the teacher's voice (a 0 dB signal-to-noise ratio) or worse.
In addition, older classrooms designed with square shapes and hard surfaces are very reverberant, further decreasing the intelligibility of speech. Reverberation is commonly described by measuring the reverberation time, the time required after the signal ceases for the signal strength to be reduced by 60 dB. In many rooms, signals strength is reduced quite quickly (perhaps less than a half-second) and no noticeable echo is present. In larger, hard-walled rooms, reverberation times may be greater than a second, and the echo is quite noticeable.
Noise and reverberation combine to produce exceptionally adverse effects on speech understanding by children with sensorineural hearing loss.
In fact, a "real" child with sensorineural hearing loss performs more poorly than this, as we cannot yet simulate the frequency and temporal distortions created by their impaired inner ear. As noise levels get worse, the performance gap between children with and without hearing loss increases.
Children with hearing loss require more favorable conditions (an improvement in signal-to-noise ratio of 12 to 15 dB) than do other children in order to achieve the same word recognition. That is, the teacher's voice must be heard by an additional 12 or 15 dB above the noise level in order for children with hearing loss to understand as well as other children in the same room. These more favorable listening conditions cannot be achieved through children's use of hearing aids alone. Traditional hearing aids place the microphone on the child's ear, and these amplify both the signal (the teacher's voice), and the noise (the children's chatter) equally. Instead, more favorable listening conditions may be achieved by providing amplification of the signal selectively. Teachers can improve the signal-to-noise ratio by wearing wireless microphones, with the voice signal transmitted through personal FM systems to individual children wearing FM receivers, or by transmitting the signal through classroom FM amplification systems to speakers around the room. These systems improve children's understanding by amplifying the teacher's voice selectively, resulting in a desirable positive signal-to-noise ratio. Additional benefit can be gained through architectural changes that result in reduced noise and reverberation in the classroom, such as sound-absorbing tiles, carpets, and drapes.
Children with hearing loss look like all other children, but they understandably experience frustration while trying to learn in unfavorable conditions. Some succeed in spite of the conditions; others may become poor readers, poor mathematics students, or behavior problems. Still, the good news is that the secondary problems associated with hearing loss (illustrated in Figure 1) can be minimized by early identification of the loss and by maximizing communication in the child's environment.
Link to Self-Help for Hard-of-Hearing Web Site