Application of Advanced Hearing Aid Technology in Pediatric Hearing Aid Fitting

Directional Microphones

Directional microphone technology was developed to improve speech perception in noise. The directional microphones amplify only the sounds which arrive from the front and reduce the noise from the surroundings. This technology is especially useful in one to one conversations and improves speech perception in noise. Previous studies on adults have reported that directional microphones improve speech perception in noise (Bentler, 2005). Gravel, Fausel, Liskow, and Chobot (1999) have reported that speech perception in noise was better among children between 4 to 11 years of age. The speech was presented directly in front (0 degrees) and noise was presented directly behind (180 degrees). Signal to noise ratio (SNR) – 50 was determined using multi-talker babble in an adaptive manner. The results of their study clearly showed improved aided performance with directional microphones compared to the omnidirectional condition.

Ricketts, Galster, and Tharpe (2007) simulated different classroom environments and determined speech perception in 26 children in the age range of 10-17. Omnidirectional and directional microphones were used to determine speech understanding abilities in presence of noise. Speech perception was better only when the speaker was in front of the child. Directional microphones do no improve speech perception when the speaker was behind or towards the side of the child. The review of the studies on the efficacy of directional hearing aids in children suggests that they help in improving speech when presented from the front and suppresses the surrounding environmental noise. However, for younger children and infants, incidental learning happens a lot and their attention moves from one speaker to another very fast. Studies have shown that children who are less than 2 years old learn to communicate by overhearing the surrounding speech in addition to direct communication (Akhtar, 2005). There are limited studies which have attempted to assess the effects of directional microphones on incidental learning in children with hearing impairment. In addition, there is a dearth of literature on the effect of directional microphones on localization abilities, which has direct implication for safety, especially in children.

Based on the literature, it is well reported that directional microphones can be recommended for older children in specific situations where the speaker is in the front and noise are from the surroundings. Frequency modulated (FM) systems provide better SNRs compared to directional microphones. However, it is not always practical when the child listens to speech babble (multiple speakers). Parents should have the option of switching between omnidirectional and directional mode depending on the listening situation. Adaptive directionality is reported to be better compared to fixed directionality. However, there are limited studies on the efficacy of adaptive directionality in children (Auriemmo, Kuk, Lau, Dornan, Sweeton, Marshall,... Stenger, 2009). The option of activating or deactivating directional microphones should be thoroughly discussed with the parents. They should also be oriented regarding the application of these hearing aids and its benefits in real life situations.