Dr. McCreery is associate director of audiology and staff scientist at Boys Town National Research Hospital in Omaha, NE.
One of the challenges of writing a regular column for The Hearing Journal about working with children who are hard of hearing is that solutions are rarely straightforward in this group. While the complexity makes working with pediatric patients a new and interesting adventure every day, it can be difficult to develop a clear consensus on important clinical issues.
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The use of directional microphones is one such issue, despite the publication of great research on the topic over the last few years. Clinicians must decide at what point during a child's development to activate directional microphones.
Directional microphones are designed to suppress sounds that originate from a particular direction relative to the listener. In some cases, sounds coming from behind or beside the listener are reduced, while the amplification of sounds from in front of the listener is maintained.
Figure. Ryan McCreer...Image Tools
The biggest advantages with directional microphones are achieved when the signal of interest is in front of the listener. Research has revealed this pattern both in adults and, as reported by Todd A. Ricketts and colleagues, in school-age children ( Am J Audiol 2007;16:130-144 http://aja.asha.org/cgi/content/abstract/16/2/130).
Seems pretty straightforward so far, right? Not so fast.
A number of considerations render the decision to activate directional microphones more complex in children than in adults. For most adult patients, directional microphones are recommended.
In order to receive the greatest benefit from directional microphones, the sound source of interest must be located in front of the listener, or the listener must orient toward the sound source with the head.
School-age children are able to orient reliably toward the teacher or other talkers in a classroom setting ( J Speech Lang Hear Res 2008;51:516-525 http://jslhr.asha.org/cgi/content/abstract/51/2/516). However, little data are available to describe whether or not infants and young children wearing hearing aids can appropriately orient their heads to benefit from directional microphones.
More recent work with school-age children and directional microphones by Todd A. Ricketts and Erin M. Picou has highlighted the importance of being able to switch the hearing aid from omnidirectional to directional settings based on the listening conditions ( Ear Hear 2013;34:601-609 http://journals.lww.com/ear-hearing/Fulltext/2013/09000/Speech_Recognition_for_Bilaterally_Asymmetric_and.8.aspx).
School-age children may be able to switch between omnidirectional and directional settings on their hearing aids with appropriate training and support, but younger children may not be able to do so reliably.
This leaves questions as to whether or not parents or caregivers should be trained to switch directional microphones for younger children and whether adaptive systems in the hearing aid that automatically switch between omnidirectional and directional settings based on the environment are appropriate. Unfortunately, recommendations to address these issues have not been reported in the literature.
Teresa Y. C. Ching and colleagues explored the potential impact of directional microphones for infants and young children by documenting the looking behavior of a group of children who were hard of hearing and a group of children with normal hearing ( J Speech Lang Hear Res 2009;52:1241-1254 http://jslhr.asha.org/cgi/content/abstract/52/5/1241).
Directional effects were modeled based on the acoustic environments, examining how often the child was facing a signal of interest across four realistic listening conditions.
The pattern of results matched expectations based on how directional microphones work and what previous studies in older children have shown: that is, the greatest advantages for directional microphones were seen when the talker was in front of the child. The decrements observed when the talker was to the side or behind the child were relatively small.
However, based on parents’ reports of listening situations, most of the young children in the study were not frequently in one-on-one communication situations where directional microphones might be most beneficial.
TAKING AGE INTO CONSIDERATION
Taken together, it might be difficult to develop a concise recommendation for whether or not directional microphones should be used with children.
I do think these data provide the basis for good clinical decision making, even if the answer is slightly more complicated than a simple, “Yes, directional microphones are always good,” or, “Directional microphones are not appropriate for children.”
Age is clearly one consideration that might influence clinicians’ decisions about directional microphones for a pediatric patient. Much stronger and consistent evidence is available for school-age children and adults than for infants and young children at this time.
When considering directional microphones based on the child's age, the emphasis should be on the developmental level of the child, rather than the chronological age. Children who cannot orient reliably toward a specific talker or have significant attention difficulties may not be ready for directional microphones at the same age as typically developing peers.
If a directional microphone is recommended, training and support should be provided so that the child can switch the microphone mode manually based on listening conditions. Further research on the adequacy of hearing aid systems that automatically switch based on the acoustic conditions of the environment could reduce the need for the child or caregiver to manage the directionality of the hearing aid.
In terms of infants and young children, their limited ability to orient toward talkers of interest combined with the small potential for decrements when the speaker is behind or to the side suggests that both the benefits and potential for negative outcomes from directional microphones are small.
Thus, other strategies for managing background noise, such as remote microphone systems, may be more appropriate for children in this age range when noise is a concern. Although such systems are not practical in every listening environment, having a remote microphone close to the talker of interest is an excellent way to minimize the negative effects of noise on perception.
Overall, directional microphones are effective for minimizing the negative consequences of background noise and are likely to be beneficial in specific listening situations for children who wear hearing aids. Clinicians who work with these children must often make decisions on whether or not to activate directional microphones based on the listening and developmental needs of the child.
References on Tap
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© 2013 by Lippincott Williams & Wilkins, Inc.