Starkey Research & Clinical Blog

Should you prescribe digital noise reduction to children?

Pittman, A. (2011). Age-related benefits of digital noise reduction for short term word learning in children with hearing loss. Journal of Speech, Language and Hearing Research 54, 1448-1463.

This editorial discusses the clinical implications of an independent research study and does not represent the opinions of the original authors.

A child’s ability to learn new words has important implications for language acquisition, mental and social development as well as academic achievement.  How easily a child acquires new vocabulary words can be affected by numerous factors, including age, working memory and current vocabulary (Alt, 2010). Hearing loss is known to adversely affect children’s ability to learn new words and the more severe the loss, the more significant the effect on word learning (Pittman, et al., 2005; Blamey et al., 2001). The effect of hearing loss on word learning may be related to a decreased ability to encode the degraded stimuli into working memory. Indeed, in a study with normal-hearing and hearing-impaired children, Pittman found that word stimuli that were modified with narrowed bandwidths were harder for children to learn (Pittman, 2008). Similar results indicating that degraded perception adversely affects children’s phonological processing have been reported elsewhere (Briscoe, et al., 2001).

In many everyday listening situations, speech must be perceived in the presence of noise or other competing sounds. Noise can degrade the speech information, making words more difficult to encode into working memory and identify correctly. Individuals with hearing loss are more adversely affected by the presence of background noise (Kochkin, 2002; McCoy et al., 2005; Picou et al., 2013), which is of particular concern when the effects of noise on word learning are considered. Hearing aids can at least partially mitigate effects of background noise with the use advanced signal processing like directional microphones and digital noise reduction (DNR). However, little evidence exists to support beneficial effects of DNR on word learning. Pittman suggests that there is reason for concern as DNR could impose negative effects on word learning because of reductions in overall amplification. Additionally, the effect of DNR on connected speech, which offers semantic and syntactic context, may be very different than the effects on isolated word learning, so the everyday experience of hearing aid users could be different from laboratory results that measured perception of isolated words.

This study examined how DNR affects word learning in hearing-impaired children with hearing aids. The authors presented these hypotheses:

1)              Word learning would decrease in noise for children with normal hearing and those with hearing loss.

2)              Word learning rates would slow in noise, due to the reduction in overall amplification imposed by DNR.

Forty-one children with normal hearing and 26 participants with mild-to-moderate hearing loss participated in the study. The treatment groups were comprised of two age sub-groups: a younger group of children from age 8-10 and a slightly older group of children from age 11-12. The children with hearing loss had been diagnosed at an average age of approximately 3 years and all but one wore personal hearing aids. Participants with hearing loss were fitted with BTE hearing aids programmed to DSL v5.0 targets, verified with real-ear measures and set with two programs. In Program 1, advanced signal processing features like noise reduction, impulse reduction, wind noise reduction and feedback management were turned off. In Program 2, these features remained disabled except for noise reduction, which was set to maximum.

Word learning was tested using nonsense words, presented in three sets of five words each. All were two-syllable words and each list contained words with the same vowels in the first and last syllables. Stimuli were presented in sound field by a female talker at a level of 50dB SPL and SNR of 0dB. Children were seated at a small table about one meter away from the speaker. Nonsense words were presented on a computer screen, along with five pictures of nonsense objects categorized as toys, flowers or aliens. The children were asked to select the appropriate picture to go with the word and were given positive reinforcement for selecting the correct picture. No reinforcement was provided for selecting the wrong picture. Children therefore learned the new words via a process of trial and error.

The first goal of the study was to examine the impact on noise on children’s word learning ability. Statistical analyses indicated that NH participants learned words faster than the HL participants did, older children learned faster than younger children and learning in quiet was faster than learning in noise. The presence of noise resulted in further decrements in performance for HL listeners, indicating that noise had a more deleterious effect on word learning in noise for participants with hearing loss than it did for normally hearing participants.

The second goal of the study was to determine if DNR affected word learning for children with hearing loss. When DNR trials were compared to quiet and noise trials, younger children performed the same in noise whether or not they were using DNR in their hearing aids. Performance for both noise conditions was significantly poorer than performance in quiet. In contrast, the performance of older participants improved with DNR, with DNR performance closely approximating performance in quiet.

When results from the word learning task were examined with reference to Peabody vocabulary scores, the results indicated that participants with hearing loss had lower vocabulary ages than the normally hearing participants. For the experimental tasks, normally hearing participants required fewer trials to reach 70% performance than the participants with hearing loss. Further analysis revealed that the age of identification, age of amplification and years of amplification use accounted for 85% of the variance, but follow-up tests revealed significant relations between word learning and age, but not word learning and hearing history. These results suggest that despite individual variability, word learning in noise was most related to the factors of age and vocabulary.

In sum, the results of this investigation suggest that DNR did not have an effect, positive or negative, on younger participants. It did improve performance for older children, however, regardless of their hearing history or years of amplification. The author points out that childrens’ speech perception in noise is known to improve with age (Elliott, 1979; Scollie, 2008) but the participants in this study demonstrated age effects only when DNR was used. It appears that the combination of DNR and greater vocabulary knowledge allowed the older listeners to demonstrate superior word learning.

There are many factors to consider when prescribing amplification characteristics for children. Word learning is a critical developmental process for children, with important implications for future social and academic accomplishments.  The documented beneficial effects of DNR on word learning in complex listening environments could be a strong motivator for selection in a pediatric hearing aid. In addition to potential word learning benefits, DNR could make amplification more comfortable in noisy conditions, thereby increasing the acceptance of hearing aids and expanding potential opportunities for communication and further word learning.

Some caution should be voiced in the selection of DNR for pediatric use. Many of these algorithms reduce frequency-specific hearing aid gains, presenting the opportunity to compromise audibility of some speech sounds when listening in noise. Prior to consideration of any DNR algorithm in pediatric populations, data should be presented that ensure the maintenance of speech audibility when that particular DNR algorithm is active and noise is presented at a levels typical of the child’s academic setting (see: Stelmachowicz et al., 2010).

The outcomes reported here provide general support for the use of DNR in school-age children. It must be clarified that the documented benefits do not suggest improved speech understanding, as this is not a function of the algorithm. Rather, the documented improvements in word learning most likely arise from the fact that noise in the absence of speech was reduced in level, reducing the effort required to listen to the individual words as they were presented.

For additional information on the prescription of hearing aid signal processing features in pediatric populations, please reference the 2013 Pedatric Amplification Guidelines, published by the American Academy of Audiology: http://audiology.org/resources/documentlibrary/Documents/PediatricAmplificationGuidelines.pdf

 

References

Alt, M. (2010). Phonological working memory impairments in children with specific language impairment: Where does the problem lie? Journal of Communication Disorders 44, 173-185.

Bentler, R., Wu, Y., Kettel, J. & Hurtig, R. (2008). Digital noise reduction: Outcomes from laboratory and field studies. International Journal of Audiology 47, 447-460.

Blamey, P., Sarant, J., Paatsch, L., Barry, J., Bow, C., Wales, R. & Rattigan, K. (2001). Relationships among speech perception, production, language, hearing loss and age in children with impaired hearing. Journal of Speech, Language and Hearing Research 44, 264-285.

Briscoe, J., Bishop, D. & Norbury, C. (2001). Phonological processing, language and literacy: a comparison of children with mild-to-moderate sensorineural hearing loss and those with specific language impairment. Journal of Child Psychology and Psychiatry and Allied Disciplines 42, 329-340.

Dunn, L. & Dunn, L. (2006). Peabody Picture Vocabulary Test – III. Circle Pines, MN:AGS.

Kochkin, S. (2002). MarkeTrak VI: 10-year customer satisfaction trends in the US hearing instrument market. The Hearing Review 9 (10), 14-25, 46.

McCoy, S.L., Tun, P.A. & Cox, L.C. (2005). Hearing loss and perceptual effort: downstream effects on older adults’ memory for speech. Quarterly Journal of Experimental Psychology A, 58, 22-33.

Picou, E.M., Ricketts, T.A. & Hornsby, B.W.Y. (2013). How hearing aids, background noise and visual cues influence objective listening effort. Ear and Hearing 34 (5).

Pittman, A., Lewis, D., Hoover, B. & Stelmachowicz, P. (2005). Rapid word learning in normal-hearing and hearing-impaired children. Effects of age, receptive vocabulary and high-frequency amplification. Ear and Hearing 26, 619-629.

Pittman, A. (2008).  Short-term word learning rate in children with normal hearing and children with hearing loss in limited and extended high-frequency bandwidths. Journal of Speech, Language and Hearing Research 51, 785-797.

Pittman, A. (2011). Age-related benefits of digital noise reduction for short term word learning in children with hearing loss. Journal of Speech, Language and Hearing Research 54, 1448-1463.

Ng, E., Rudner, M., Lunner, T., Syskind Pedersen, M. & Rönnberg, J. (2013).  Effects of noise and working memory capacity on memory processing of speech for hearing aid users. International Journal of Audiology, Early Online: 1–9

Ricketts, T. & Hornsby, B. (2005). Sound quality measures for speech in noise through a commercial hearing aid implementing digital noise reduction. Journal of the American Academy of Audiology 16, 270-277.

Sarampalis, A., Kalluri, S. & Edwards, B. (2009). Objective measures of listening effort: effects of background noise and noise reduction. Journal of Speech Language and Hearing Research 52, 1230-1240.

Stelmachowicz, P., Lewis, D., Hoover, B., Nishi, K., McCreery, R. & Woods, W. (2010). Effects of digital noise reduction on speech perception for children with hearing loss. Ear and Hearing 31, 245-355.