Denis Byrne, Harvey Dillon, Teresa Ching, Richard Katsch, Gitte Keidser

J Am Acad Audiol 12:37-51 (2001)

Abstract

A new procedure for fitting non-linear hearing aids (NAL-NL1) is described. The rationale is to maximize speech intelligibility while constraining loudness to be normal or less. Speech intelligibility is predicted by the Speech Intelligibility Index (SII) which has been modified to account for the reduction in performance associated with increasing degrees of hearing loss, especially at the high frequencies. Prescriptions are compared for the NAL-NL1, DSL [i/o], FIG6, and a threshold version of IHAFF procedures. For an average speech input level the NAL-NL1 prescriptions are very similar to those of the well-established NAL-RP procedure. Compared with the other procedures, NAL-NL1 prescribes less low-frequency gain for flat and upward sloping audiograms. It prescribes less high-frequency gain for steeply sloping high-frequency hearing losses. NAL-NL1 tends to prescribe less compression than the other procedures. All procedures differ considerably from one another for some audiograms.