NAL vs DSL in Three-Year-Olds
In 2010, Ching et al concluded that to achieve optimum audibility for soft speech, children required more gain than NAL-NL1 prescribed, and to achieve listening comfort in noise, children required less gain than DSLv4.1 prescribed.
In 2013, Ching and colleagues reported a randomized controlled study involving 218 children with bilateral sensorineural hearing loss (SNHL). Objective measures were gathered at 6 and 12 months post hearing aid fitting and at age 3 years. All children were randomly assigned and fitted bilaterally with NAL or DSL using wide dynamic range compression instruments. The authors report a "team of qualified speech pathologists" were blinded with regard to the child’s hearing aid characteristics (NAL or DSL) and they administered a range of tests including the Preschool Language Scale, the Peabody Picture Vocabulary Test, and the Diagnostic Evaluation of Articulation and Phonology Test. The speech pathologists rated the children’s speech intelligibility and they also gathered questionnaires from the parents.
Ching and colleagues report that overall DSL prescribed more low-frequency gain (resulting in flatter slopes) and more overall gain that NAL. Of concern, on average, the group of 218 children performed slightly poorer than 1 standard deviation below the norm for speech, language, and functional performance outcomes at age 3 years. However, the baseline performances of the children fitted with either NAL or DSL were similar. No statistically significant differences were determined between the groups of children fitted with NAL or DSL with respect to speech, language, or other functional measures. Factors that were statistically significant (with respect to language and functional performance) were socio-economic status and maternal educational level. Ching and colleagues summarized, "There was no significant association between choice of hearing aid prescription and variance in children’s speech production, language, and functional performance at 3 years of age."
For More Information, References, and Recommendations
Ching TYC, Scollie SD, Dillon H, Seewald R. (2010) A Cross-Over, Double-Blind Comparison of the NAL-NL1 and the DSL v4.1 Prescriptions for Children with Mild-to-Moderately Severe Hearing Loss. International Journal of Audiology 49:S4–S15.
Ching TYC, Dillon H, Hou S, Zhang V, Day J, Crowe K, Marnane V, Street L, Burns L, Van Buynder P, Flynn C, Thomson J. (2013) A Randomized Controlled Comparison of NAL and DSL Prescriptions for Young Children—Hearing Aid Characteristics and Performance Outcomes at Three Years of Age. International Journal of Audiology 52:S17–S28.