Better Classroom Hearing for Children with APD

An FM system improves the signal to noise ratio in the classroom..

When it comes to hearing and listening, children are not small adults. In fact, children require a signal to noise ratio of +11dB to understand 80% in a task of word recognition whereas an adult only requires a +4dB signal to noise ratio to achieve the same score. What exactly does that mean? It means that for children, the speaker’s voice has to be 11dB (dB = decibels, a unit of sound measurement) louder than the background noise for them to understand 80% of the message.

Adults have a more developed cognitive system and can cope with listening and following in complex situations.  Adults also have a larger vocabulary to help fill in the blanks when noise may obscure all or part of a word.

This need for a better signal to noise ratio is especially important in children auditory processing disorders (APD). In a typical school day, the signal to noise ratio will change depending on the speaker, external noise, classroom noise, and classroom acoustics. Studies suggest that normal hearing children, seated in the middle to rear of a typical classroom, are at a disadvantage. Students not seated near the teacher have greater difficulty understanding speech due to the decline in the teacher's voice over distance. Quite simply, classrooms are too noisy for the teacher’s voice to be heard well by every student.

An FM system is a wireless system designed to help someone better identify and understand speech in noisy situations and over distances of up to 15 meters (50 feet).

Some FM systems work together with hearing aids, while others are designed for those with normal hearing. The person speaking wears or holds a transmitter microphone (or places this in the middle of a group). This transmitter picks up important speech sounds and uses harmless radio waves to send these to one or more FM receivers, which a child wears behind the ear or connected to their hearing aids.

This results in the child receiving the teacher’s words directly in their ears, without any distracting background noise, allowing them to hear and understand well.

For children with APD, hearing sensitivity is usually normal. We know that APD negatively impacts speech perception, academic performance, on-task behavior, as well as emotional and psychological health.

Johnston et al‘s study compared children diagnosed with APD using FM to children without APD not using FM. All subjects had normal hearing.

Children with APD using FM showed improved academic performance after only five months. The Listening Inventory for Education (LIFE) pre-versus-post treatment (FM) effects demonstrated benefits across the majority of domains with significant improvements in "teacher in front of room, teacher talking with back turned" and, "other students making noise." Psychosocial status was also found to be improved five months post-FM with regard to parent and student ratings of focus-of-control, anxiety, depression, and interpersonal relationships.

The study authors found long-term benefits of FM with regard to academic, emotional, and psychosocial status and with regard to speech-perception abilities. They recommend "binaural fitting for personal FM use for children with APD" consistent with published findings. Further, they recommend annual evaluation of children with APD (for those with and without intervention) to monitor the status of their auditory processing ability.



School Planning and Management, April 2005; "Acoustical Design Basis of a Sound Education."

Finitzo-Hieber, T., Tillman T., "Room Acoustics Effects on Monosyllabic Word Discrimination Ability for Normal and Hearing Impaired Children," Journal of Speech and Hearing Research, Vol. 21, 1978, pp. 440-458.

Crandell C., Bess, F., "Speech Recognition of Children in a 'Typcial' Classroom Setting." ASHA, Vol. 29, 1986, pp.87

Johnston KN, John AB, Kreisman NV, Hall JW, Crandell CC. (2009) Multiple Benefits of Personal FM System Use by Children with Auditory Processing Disorder (APD). International Journal of Audiology (48)6:371-383.


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