Did you know that generic target rules, such as NAL-NL1, are sometimes altered in fitting software?
Targets for NAL-NL1 and other generic prescriptions may vary for the same audiogram in different manufacturer fitting software. This is because some manufacturers change the targets for their specific devices. This is often indicated by an “*” following the prescription name, although the asterisk may also indicate the opposite…that this is the original prescription. It also may not be indicated at all! The reasons for altering a generic prescription may be to account for compression parameters that the original prescription was not designed for, to accommodate open fit acoustics, or simply to facilitate immediate patient acceptance and reduce the likelihood of feedback. Although these may be considered valid reasons for altering a generic prescription, this practice can lead audiologists to think they are applying a rationale that they in reality are not.
At ReSound we recommend Audiogram+ for fitting our hearing instruments, but recognize that generic prescriptions supported by peer-reviewed research may be preferred by some professionals or for particular patients. Therefore, we strive to implement these generic prescriptions as intended by the developers, and we verify the actual gains attained in the devices on different clinical verification equipment* as part of the fitting software development process.
As an example of how differently manufacturers can implement the same generic prescription, the graph below shows REIG targets for a speech-weighted 50 dB SPL signal generated by NAL-NL1 Standalone software, Aventa 3, and another fitting software for the same audiogram (mild-to-moderately sloping). Closed BTE devices were selected, and the experience level was set to the highest level for both ReSound and the other fitting software (NAL-NL1 does not account for user experience). As shown in the graph, the Aventa targets are very similar to those generated by the NAL-NL1 standalone software while those from the other fitting software were significantly lower. When choosing generic prescriptions in Aventa, the fitter can be confident that the settings applied are consistent with the original formula.
*Across equipment results for the same fitting rationale have been reported, so it is important to know how devices programmed to a certain prescription in Aventa will look when using different clinical verification equipment.
Mueller G, Ricketts T. Whose NAL-NL fitting method are you using? The Hearing Journal. 2009, 62(8):10-17. http://journals.lww.com/thehearingjournal/Fulltext/2009/08000/Whose_NAL_NL_fitting_method_are_you_using_.3.aspx