Evidence, Outcomes, and Pediatric Amplification Issues
Ching (2012) offers a new and comprehensive evidence-based guide (for clinicians) with regard to maximizing modern hearing aid amplification outcomes for children. In her review of technology and pragmatics, she notes the primary goals of amplification include providing audibility across the widest possible bandwidth—at a comfortable listening level.
Ching notes that the major prescription rules (DSL and NAL) incorporate wide dynamic range compression (WDRC) and the evidence demonstrates that for children with mild-to-moderately/severe hearing losses, WDRC is associated with improved speech perception and horizontal localization with low-level inputs. Further, she reports evidence suggests WDRC facilitates “improved functional performance in real-world environments.” However, and of note, “...the best compression thresholds for children is currently unknown.”
Ching reports that compression ratios below 3:1 have not been associated with degradations in performance. With regard to short vs. long release times, she states that with specific regard to children, it is simply not known whether children should be prescribed short/fast (<100 msec) or long/slow (>500 msec) release times—and there is little scientific evidence to support either across single or multiple listening situations.
With regard to extended high-frequency bandwidths in hearing aid fittings for children with severe-to-profound hearing loss, Ching reports “no research has investigated the usefulness of extended amplification bandwidth for children with severe or profound hearing loss." The author reports research to date on frequency transposition (FT) and frequency compression (FC) (to increase high frequency audibility) suggests children (and adults) fitted with new FT or FC devices prefer them to their own devices, although the reasoning is not well understood. Ching notes that when one superimposes a shifted signal onto a previously present signal, artifacts result and “compression necessarily reduces spectral contrasts (known to be) important for speech discrimination....” She summarizes that there exists insufficient evidence to recommend for/against frequency lowering for infants and children.
Importantly, she also notes that frequency-lowering should be evaluated prior to recommending cochlear implantation (in appropriate candidates). With regard to listening in noise, Ching reports the largest improvements have occurred in wireless technologies, such as FM. With regard to noise reduction (NR) systems she reports insufficient evidence exists to recommend for or against the use of NR for infants and children. With regard to directional microphones (DMs), Ching reports proven benefits of directionality in children and she notes “unnecessary concerns” with regard to reducing audibility from listener's sides and rear.
For More Information, References, and Recommendations
Ching TYC. (2012) "Hearing Aids For Children." Chapter Five: 93-118 in "Evidence-Based Practice in Audiology—Evaluating Interventions for Children and Adults With Hearing Impairment." Plural Publishing, 2012. Eds. Wong. L, Hickson L