Investigation of hearing aid fitting according to the national acoustic laboratories' prescription for non-linear hearing aids and the desired sensation level methods in Japanese speakers: a crossover-controlled trial.

OBJECTIVE: Some studies have directly compared the National Acoustic Laboratories' prescription for non-linear hearing aids (HAs) version 2 (NAL-NL2) and Desired Sensation Level for non-linear HAs version 5 (DSLv5), although none were performed in Japan. As the Japanese language is a tonal language that has different linguistic characteristics than those of the studied languages, we compared the outcomes of the NAL-NL2 and DSLv5 in hearing-impaired Japanese participants. METHODS: A crossover-controlled trial was conducted on 18 first-time HA users with bilateral moderate sensorineural hearing loss. Participants wore HAs adjusted with each prescriptive method for four weeks. The prescriptions were assessed using speech discrimination testing and the abbreviated profile of hearing aid benefit (APHAB). Consequently, participants were asked to select their preferred prescription and determine which was better for "listening to a conversation" and when "noisy." RESULTS: The mean DSLv5 real ear insertion gain for an input level of 65 dB sound pressure level (SPL) was higher than that of the NAL-NL2 at 250 and 500 Hz. The average speech discrimination score was 78 ± 14% at a 65-dB SPL and 75 ± 17% at an 80-dB SPL for the NAL-NL2, and 79 ± 11% at a 65-dB SPL and 77 ± 17% at an 80-dB SPL for the DSLv5. These differences were not significant. No significant differences were observed in APHAB subscale scores between the two prescription methods. Ultimately, 11 (61%) and 7 (39%) participants preferred the NAL-NL2 and DSLv5, respectively, with no significant differences. CONCLUSION: Although the gain of the NAL-NL2 is smaller than that of the DSLv5, both had the same hearing effect. Therefore, the NAL-NL2 may be more useful than the DSLv5 in Japanese.

Comparison of real-ear insertion gains in Japanese-speaking individuals wearing hearing aids with DSLv5 and NAL-NL2.

OBJECTIVE: We used real-ear insertion gain (REIG), with the international speech test signal (ISTS), to evaluate the amplifying characteristics of hearing aids, set for patients who have been wearing such aids for a long time in a stable manner. We further compared this to the target values of the DSLv5 and NAL-NL2 methods. METHODS: The subjects were adults with moderate sensorineural hearing loss. We examined 40 ears in 25 individuals (15 people wearing hearing aids in both ears and ten people wearing aid in only one ear). Fit assessments were performed based on the speech performance-intensity functions and tolerance of environmental noise, and the ears studied were categorized as either ears with sufficient benefit or ears with insufficient benefit. Additionally, we evaluated the REIG for international speech test signals at 65-dB and 80-dB sound pressure level (SPL). We compared the REIG and target values for voice input at 65-dB and 80-dB SPL, calculated from the DSLv5 and NAL-NL2 methods. RESULTS: Among the 40 ears, 34 received sufficient benefit and six received an insufficient benefit from hearing aids. The REIG for ISTS at 65-dB in the sufficient benefit ears, at frequencies of 1,000 Hz and 2,000 Hz, were similar to the target values of NAL-NL2 and DSLv5 but were significantly lower at 250 Hz, 500 Hz, and 4,000 Hz frequencies. The compression ratio of REIG for sufficient benefit ears was similar to that of DSLv5. The REIG for ISTS at 65-dB in the insufficient benefit ears was smaller than that in the sufficient benefit ears at frequencies of 2,000 Hz and 4,000 Hz. CONCLUSION: This study suggested that the target values of NAL-NL2 and DSLv5 are appropriate, even for Japanese-speaking individuals, at mid-pitch sounds. Although it is necessary to investigate the necessity for low-pitch and high-pitch gains further in the future, this study provides meaningful data regarding the amplifying characteristics in Japanese-speaking individuals who have been wearing hearing aids in a stable manner.