Functional outcomes for speech-in-noise intelligibility of NAL-NL2 and DSL v.5 prescriptive fitting rules in hearing aid users

Abstract

Purpose: The primary aim of this research study is to assess whether differences exist in the application of the NAL-NL2 and DSL v.5 prescription formulas in terms of speech-in-noise intelligibility.

Methods: Data from 43 patients, were retrospectively evaluated and analyzed. Inclusion criteria were patients with bilateral conductive, sensorineural, or mixed hearing loss, already using hearing aids for at least 1 year, and aged 18 years or older. Patients were categorized into two groups based on the prescriptive method employed by the hearing aid: NAL-NL2 or DSL v.5. Pure tone audiometry, speech audiometry, free field pure tone and speech audiometry with the hearing aid, and Matrix sentence test were performed. The Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire was used to assess the personal audiological benefit provided by the hearing aid.

Results: No statistically significant differences were found comparing the free-field pure tone average (FF PTA) and the free-field Word Recognition Score (FF WRS). Comparing the Speech Reception Threshold (SRT) parameter of patients with NAL-NL2 vs DSL v.5, no statistically significant difference was found, thus highlighting a condition of comparability between the two prescription methods in terms of speech-in-noise intelligibility. Comparing the results of the APHAB questionnaire, no statistically significant differences were evident for all subscales and overall benefit. When conducting a comparison between male and female patients using the NAL-NL2 method, no differences were observed in SRT values, however, the APHAB questionnaire revealed a difference in the AV subscale score for the same subjects.

Conclusion: Our analysis revealed no statistically significant differences in speech-in-noise intelligibility, as measured by the SRT values from the Matrix Sentence Test, when comparing the two prescriptive methods. This compelling result reinforces the notion that, functionally, both methods are comparably effective in enhancing speech intelligibility in real-world, noisy environments. However, it is crucial to underscore that the absence of differences does not diminish the importance of considering individual patient needs and preferences in the selection of a prescriptive method.

Keywords: DSL; Matrix test; NAL; Prescription formula; Prescription procedure; Real ear measurements.