Pediatric Amplification Perspectives 2014: Part 2
Dillon, Ching, and Golding (2014) report commercially available hearing aids are available that switch automatically from omni to directional mode (if and only if) the directional mode has a superior signal-to-noise ratio (SNR). Further, it is well known and has been consistently demonstrated that children require a more advantageous SNR than do adults, and it is far more likely that adaptive directionality will provide a listening advantage rather than a disadvantage. Therefore, the authors recommend that all children with head control (approximately 6 months of age and older) be fitted with automatic switching directional microphones as a matter of course."
With regard to frequency lowering, results across the last decades have produced mixed results. Dillon, Ching, and Golding conclude that "frequency lowering can sometimes increase intelligibility but not all frequency lowering schemes have positive results." They report there is not enough information available to decide which patient would do best with which frequency lowering protocol. Nonetheless, Dillon, Ching, and Golding note that given the range of outcomes, the multiple frequency-lowering protocols and the diverse audiogram results that might indicate candidacy for frequency lowering, they say "it is difficult to give firm, evidence based recommendations" with regard to who might benefit and which protocol to use. They report frequency lowering sophistication has increased lately. However, it is noteworthy that children who do not do well with conventional amplification "are now extremely likely to benefit from cochlear implantation." They report the need for effective frequency lowering hearing aids has been reduced while availability has increased.
The accuracy of the audiogram is clearly paramount. However, Dillon, Ching, and Golding report that audiograms are typically calibrated for adult ears, which will not be the same for children due to their reduced size (i.e., shorter and narrower) external auditory canals (EACs). As the child grows, their EACs increases in size while the concomitant SPL (sound pressure level) at the eardrum decreases, creating the "apparent" decrease in hearing thresholds as the child ages. Further, different transducers (earphones, inserts, sound field speakers) yield different results. Therefore, to obtain accurate thresholds from a child, the Seewald and Scollie (2003) protocol can be performed automatically in DSL software, which expresses thresholds in terms of dB SPL at the eardrum (using the RECD to convert thresholds in dB HL to ear canal SPL). Another option is to report thresholds in terms of "adult equivalent hearing level," which can be automatically derived via NAL software.
For More Information, References, and Recommendations
Dillon H, Ching T, Golding M. (2014) "Hearing Aids For Infants and Children." Chapter 20, pages 209 to 227, in Pediatric Audiology Diagnosis, Technology and Management. Second Edition. Editors; Jane Madell and Carol Flexer. Thieme Medical Publishers, Inc.